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Spatiotemporal changes in water, land use, and ecosystem services in Central Asia considering climate changes and human activities
YU Yang, CHEN Xi, Ireneusz MALIK, Malgorzata WISTUBA, CAO Yiguo, HOU Dongde, TA Zhijie, HE Jing, ZHANG Lingyun, YU Ruide, ZHANG Haiyan, SUN Lingxiao
Journal of Arid Land    2021, 13 (9): 881-890.   DOI: 10.1007/s40333-021-0084-3
Abstract156)   HTML20)    PDF (472KB)(234)      

Central Asia is located in the hinterland of Eurasia, comprising Kazakhstan, Uzbekistan, Kyrgyzstan, Turkmenistan, and Tajikistan; over 93.00% of the total area is dryland. Temperature rise and human activities have severe impacts on the fragile ecosystems. Since the 1970s, nearly half the great lakes in Central Asia have shrunk and rivers are drying rapidly owing to climate changes and human activities. Water shortage and ecological crisis have attracted extensive international attention. In general, ecosystem services in Central Asia are declining, particularly with respect to biodiversity, water, and soil conservation. Furthermore, the annual average temperature and annual precipitation in Central Asia increased by 0.30°C/decade and 6.9 mm/decade in recent decades, respectively. Temperature rise significantly affected glacier retreat in the Tianshan Mountains and Pamir Mountains, which may intensify water shortage in the 21st century. The increase in precipitation cannot counterbalance the aggravation of water shortage caused by the temperature rise and human activities in Central Asia. The population of Central Asia is growing gradually, and its economy is increasing steadily. Moreover, the agricultural land has not been expended in the last two decades. Thus, water and ecological crises, such as the Aral Sea shrinkage in the 21st century, cannot be attributed to agriculture extension any longer. Unbalanced regional development and water interception/transfer have led to the irrational exploitation of water resources in some watersheds, inducing downstream water shortage and ecological degradation. In addition, accelerated industrialization and urbanization have intensified this process. Therefore, all Central Asian countries must urgently reach a consensus and adopt common measures for water and ecological protection.

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Reducing water and nitrogen inputs combined with plastic mulched ridge-furrow irrigation improves soil water and salt status in arid saline areas, China
LI Cheng, WANG Qingsong, LUO Shuai, QUAN Hao, WANG Naijiang, LUO Xiaoqi, ZHANG Tibin, DING Dianyuan, DONG Qin'ge, FENG Hao
Journal of Arid Land    2021, 13 (8): 761-776.   DOI: 10.1007/s40333-021-0015-3
Abstract123)   HTML26)    PDF (710KB)(103)      

Plastic mulched ridge-furrow irrigation is a useful method to improve crop productivity and decrease salt accumulation in arid saline areas. However, inappropriate irrigation and fertilizer practices may result in ecological and environmental problems. In order to improve the resource use efficiency in these areas, we investigated the effects of different irrigation amounts (400 (I1), 300 (I2) and 200 (I3) mm) and nitrogen application rates (300 (F1) and 150 (F2) kg N/hm2) on water consumption, salt variation and resource use efficiency of spring maize (Zea mays L.) in the Hetao Irrigation District (HID) of Northwest China in 2017 and 2018. Result showed that soil water contents were 0.2%-8.9% and 13.9%-18.1% lower for I2 and I3 than for I1, respectively, but that was slightly higher for F2 than for F1. Soil salt contents were 7.8%-23.5% and 48.5%-48.9% lower for I2 than for I1 and I3, but that was 1.6%-5.5% higher for F1 than for F2. Less salt leaching at the early growth stage (from sowing to six-leaf stage) and higher salt accumulation at the peak growth stage (from six-leaf to tasseling stage and from grain-filling to maturity stage) resulted in a higher soil salt content for I3 than for I1 and I2. Grain yields for I1 and I2 were significantly higher than that for I3 and irrigation water use efficiency for I2 was 14.7%-34.0% higher than that for I1. Compared with F1, F2 increased the partial factor productivity (PFP) of nitrogen fertilizer by more than 80%. PFP was not significantly different between I1F2 and I2F2, but significantly higher than those of other treatments. Considering the goal of saving water and nitrogen resources, and ensuring food security, we recommended the combination of I2F2 to ensure the sustainable development of agriculture in the HID and other similar arid saline areas.

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Soil quality assessment in different dammed-valley farmlands in the hilly-gully mountain areas of the northern Loess Plateau, China
CHEN Shumin, JIN Zhao, ZHANG Jing, YANG Siqi
Journal of Arid Land    2021, 13 (8): 777-789.   DOI: 10.1007/s40333-021-0014-4
Abstract112)   HTML17)    PDF (1224KB)(314)      

There are numerous valley farmlands on the Chinese Loess Plateau (CLP), where suffers from low soil quality and high risk of soil salinization due to the shallow groundwater table and poor drainage system. Currently, research on the evolution processes and mechanisms of soil quality and salinization in these dammed-valley farmlands on the CLP is still inadequately understood. In this study, three kinds of dammed-valley farmlands in the hilly-gully areas of the northern CLP were selected, and the status of soil quality and the impact factors of soil salinization were examined. The dammed-valley farmlands include the new farmland created by the project of Gully Land Consolidation, the 60-a farmland created by sedimentation from check dam, and the 400-a farmland created by sedimentation from an ancient landslide-dammed lake. Results showed that (1) the newly created farmland had the lowest soil quality in terms of soil bulk density, porosity, soil organic carbon and total nitrogen among the three kinds of dammed-valley farmlands; (2) soil salinization occurred in the middle and upper reaches of the new and 60-a valley farmlands, whereas no soil salinization was found in the 400-a valley farmland; and (3) soil salinization and low soil nutrient were determined to be the two important factors that impacted the soil quality of the valley farmlands in the hilly-gully mountain areas of the CLP. We conclude that the dammed-valley farmlands on the CLP have a high risk of soil salinization due to the shallow groundwater table, alkalinity of the loessial soil and local landform feature, thus resulting in the low soil quality of the valley farmlands. Therefore, strengthening drainage and decreasing groundwater table are extremely important to improve the soil quality of the valley farmlands and guarantee the sustainable development of the valley agriculture on the CLP.

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Synergistic effects of multiple driving factors on the runoff variations in the Yellow River Basin, China
WANG Junjie, SHI Bing, ZHAO Enjin, CHEN Xuguang, YANG Shaopeng
Journal of Arid Land    2021, 13 (8): 835-857.   DOI: 10.1007/s40333-021-0078-1
Abstract98)   HTML13)    PDF (8557KB)(59)      

River runoff plays an important role in watershed ecosystems and human survival, and it is controlled by multiple environmental factors. However, the synergistic effects of various large-scale circulation factors and meteorological factors on the runoff on different time-frequency scales have rarely been explored. In light of this, the underlying mechanism of the synergistic effects of the different environmental factors on the runoff variations was investigated in the Yellow River Basin of China during the period 1950-2019 using the bivariate wavelet coherence (WTC) and multiple wavelet coherence (MWC) methods. First, the continuous wavelet transform (CWT) method was used to analyze the multiscale characteristics of the runoff. The results of the CWT indicate that the runoff exhibited significant continuous or discontinuous annual and semiannual oscillations during the study period. Scattered inter-annual time scales were also observed for the runoff in the Yellow River Basin. The meteorological factors better explained the runoff variations on seasonal and annual time scales. The average wavelet coherence (AWC) and the percent area of the significant coherence (PASC) between the runoff and individual meteorological factors were 0.454 and 19.89%, respectively. The circulation factors mainly regulated the runoff on the inter-annual and decadal time scales with more complicated phase relationships due to their indirect effects on the runoff. The AWC and PASC between the runoff and individual circulation factors were 0.359 and 7.31%, respectively. The MWC analysis revealed that the synergistic effects of multiple factors should be taken into consideration to explain the multiscale characteristic variations of the runoff. The AWC or MWC ranges were 0.320-0.560, 0.617-0.755, and 0.819-0.884 for the combinations of one, two, and three circulation and meteorological factors, respectively. The PASC ranges were 3.53%-33.77%, 12.93%-36.90%, and 20.67%-39.34% for the combinations one, two, and three driving factors, respectively. The combinations of precipitation, evapotranspiration (or the number of rainy days), and the Arctic Oscillation performed well in explaining the variability in the runoff on all time scales, and the average MWC and PASC were 0.847 and 28.79%, respectively. These findings are of great significance for improving our understanding of hydro-climate interactions and water resources prediction in the Yellow River Basin.

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Diversity of cultivable endophytic bacteria associated with halophytes in Xinjiang of China and their plant beneficial traits
LI Li, GAO Lei, LIU Yonghong, FANG Baozhu, HUANG Yin, Osama A A MOHAMAD, Dilfuza EGAMBERDIEVA, LI Wenjun, MA Jinbiao
Journal of Arid Land    2021, 13 (8): 790-800.   DOI: 10.1007/s40333-021-0016-2
Abstract94)   HTML13)    PDF (550KB)(101)      

Endophytic bacteria from halophytes have a wide range of application prospects in various fields, such as plant growth-promoting, biocontrol activity and stress resistance. The current study aimed to identify cultivable endophytic bacteria associated with halophytes grown in the salt-affected soil in Xinjiang Uygur Autonomous Region, China and to evaluate their plant beneficial traits and enzyme-producing activity. Endophytic bacteria were isolated from Reaumuria soongorica (PalL Maxim.), Artemisia carvifolia (Buch.-Ham. ex Roxb. Hort. Beng.), Peganum harmala L. and Suaeda dendroides (C. A. Mey. Moq.) by using the cultural-dependent method. Then we classified these bacteria based on the difference between their sequences of 16S rRNA (16S ribosomal RNA) gene. Results showed that the isolated bacteria from R. soongorica belonged to the genera Brucella, Bacillus and Variovorax. The bacteria from A. carvifolia belonged to the genera Micromonospora and Brucella. The bacteria from P. harmala belonged to the genera Paramesorhizobium, Bacillus and Peribacillus. The bacteria from S. dendroides belonged to the genus Bacillus. Notably, the genus Bacillus was detected in the three above plants, indicating that Bacillus is a common taxon of endophytic bacteria in halophytes. And, our results found that about 37.50% of the tested strains showed strong protease-producing activity, 6.25% of the tested strains showed strong cellulase-producing activity and 12.50% of the tested strains showed moderate lipase-producing activity. Besides, all isolated strains were positive for IAA (3-Indoleacetic acid) production, 31.25% of isolated strains exhibited a moderate phosphate solubilization activity and 50.00% of isolated strains exhibited a weak siderophore production activity. Our findings suggest that halophytes are valuable resources for identifying microbes with the ability to increase host plant growth and health in salt-affected soils.

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Mathematical and statistical modeling of morphometric and planar parameters of barchans in Pashoeyeh Erg in the west of Lut Desert, Iran
Hossein GHAZANFARPOUR, Mohsen POURKHOSRAVANI, Sayed H MOUSAVI, Ali MEHRABI
Journal of Arid Land    2021, 13 (8): 801-813.   DOI: 10.1007/s40333-021-0102-5
Abstract94)   HTML9)    PDF (444KB)(80)      

Barchan dunes are among the most common accumulative phenomena made by wind erosion, which are usually formed in regions where the prevailing wind direction is almost constant throughout the year and there is not enough sand to completely cover the land surface. Barchans are among the most common windy landscapes in Pashoueyeh Erg in the west of Lut Desert, Iran. This study aims to elaborate on morphological properties of barchans in this region using mathematical and statistical models. The results of these methods are very important in investigating barchan shapes and identifying their behavior. Barchan shapes were mathematically modeled by simulating them in the coordinate system through nonlinear parabolic equations, so that two separate equations were calculated for barchan windward and slip-face parabolas. The type and intensity of relationships between barchan morphology and mathematical parameters were determined by the statistical modeling. The results indicated that the existing relationships followed the power correlation with the maximum coefficient of determination and minimum error of estimate. Combining the above two methods is a powerful basis for stimulating barchans in virtual and laboratory environments. The most important result of this study is to convert the mathematical and statistical models of barchan morphology to each other. Focal length is one of the most important parameters of barchan parabolas, suggesting different states of barchans in comparison with each other. As the barchan's focal length decreases, its opening becomes narrower, and the divergence of the barchan's horns reduces. Barchans with longer focal length have greater width, dimensions, and volume. In general, identifying and estimating the morphometric and planar parameters of barchans is effective in how they move, how much they move, and how they behave in the environment. These cases play an important role in the management of desert areas.

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Ecosystem service values of gardens in the Yellow River Basin, China
GE Qianqian, XU Wenjie, FU Meichen, HAN Yingxin, AN Guoqiang, XU Yuetong
Journal of Arid Land    2022, 14 (3): 284-296.   DOI: 10.1007/s40333-022-0061-5
Abstract92)   HTML37)    PDF (802KB)(244)      

Studies on the ecosystem service value (ESV) of gardens are critical for informing evidence- based land management practices based on an understanding of the local ecosystem. By analyzing equivalent value factors (EVFs), this paper evaluated the values of 11 ecosystem services of gardens in the Yellow River Basin of China in 2019. High-precision land use survey data were used to improve the accuracy of the land use classification, garden areas, and spatial distribution of the ESVs of gardens. The results showed that garden ecosystem generally had high ESVs, especially in terms of the ESV of food production, which is worthy of further research and application to the practice of land use planning and management. Specifically, the value of one standard EVF of ecosystem services in 2019 was 3587.04 CNY/(hm2•a), and the ESV of food production of gardens was much higher than that of croplands. Garden ecosystem provided an ESV of 1348.66×108 CNY/a in the Yellow River Basin. The areas with the most concentrated ESVs of gardens were located in four regions: downstream in the Shandong-Henan zone along the Yellow River, mid-stream in the Shanxi-Shaanxi zone along the Yellow River, the Weihe River Basin, and upstream in the Qinghai-Gansu-Ningxia-Inner Mongolia zone along the Yellow River. The spatial correlation of the ESVs in the basin was significant (global spatial autocorrelation index Moran's I=0.464), which implied that the characteristics of high ESVs adjacent to high ESVs and low ESVs adjacent to low ESVs are prominent. In the Yellow River Basin, the contribution of the ESVs of gardens to the local environment and economy varied across regions. We also put forward some suggestions for promoting the construction of ecological civilization in the Yellow River Basin. The findings of this study provide important contributions to the research of ecosystem service evaluation in the Yellow River Basin.

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Plant cover as an estimator of above-ground biomass in semi-arid woody vegetation in Northeast Patagonia, Argentina
Laura B RODRIGUEZ, Silvia S TORRES ROBLES, Marcelo F ARTURI, Juan M ZEBERIO, Andrés C H GRAND, Néstor I GASPARRI
Journal of Arid Land    2021, 13 (9): 918-933.   DOI: 10.1007/s40333-021-0083-4
Abstract91)   HTML5)    PDF (1377KB)(196)      

The quantification of carbon storage in vegetation biomass is a crucial factor in the estimation and mitigation of CO2 emissions. Globally, arid and semi-arid regions are considered an important carbon sink. However, they have received limited attention and, therefore, it should be a priority to develop tools to quantify biomass at the local and regional scales. Individual plant variables, such as stem diameter and crown area, were reported to be good predictors of individual plant weight. Stand-level variables, such as plant cover and mean height, are also easy-to-measure estimators of above-ground biomass (AGB) in dry regions. In this study, we estimated the AGB in semi-arid woody vegetation in Northeast Patagonia, Argentina. We evaluated whether the AGB at the stand level can be estimated based on plant cover and to what extent the estimation accuracy can be improved by the inclusion of other field-measured structure variables. We also evaluated whether remote sensing technologies can be used to reliably estimate and map the regional mean biomass. For this purpose, we analyzed the relationships between field-measured woody vegetation structure variables and AGB as well as LANDSAT TM-derived variables. We obtained a model-based ratio estimate of regional mean AGB and its standard error. Total plant cover allowed us to obtain a reliable estimation of local AGB, and no better fit was attained by the inclusion of other structure variables. The stand-level plant cover ranged between 18.7% and 95.2% and AGB between about 2.0 and 70.8 Mg/hm2. AGB based on total plant cover was well estimated from LANDSAT TM bands 2 and 3, which facilitated a model-based ratio estimate of the regional mean AGB (approximately 12.0 Mg/hm2) and its sampling error (about 30.0%). The mean AGB of woody vegetation can greatly contribute to carbon storage in semi-arid lands. Thus, plant cover estimation by remote sensing images could be used to obtain regional estimates and map biomass, as well as to assess and monitor the impact of land-use change on the carbon balance, for arid and semi-arid regions.

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Spatial-temporal variations of ecological vulnerability in the Tarim River Basin, Northwest China
BAI Jie, LI Junli, BAO Anmin, CHANG Cun
Journal of Arid Land    2021, 13 (8): 814-834.   DOI: 10.1007/s40333-021-0079-0
Abstract87)   HTML12)    PDF (4053KB)(139)      

As the largest inland river basin of China, the Tarim River Basin (TRB), known for its various natural resources and fragile environment, has an increased risk of ecological crisis due to the intensive exploitation and utilization of water and land resources. Since the Ecological Water Diversion Project (EWDP), which was implemented in 2001 to save endangered desert vegetation, there has been growing evidence of ecological improvement in local regions, but few studies have performed a comprehensive ecological vulnerability assessment of the whole TRB. This study established an evaluation framework integrating the analytic hierarchy process (AHP) and entropy method to estimate the ecological vulnerability of the TRB covering climatic, ecological, and socioeconomic indicators during 2000-2017. Based on the geographical detector model, the importance of ten driving factors on the spatial-temporal variations of ecological vulnerability was explored. The results showed that the ecosystem of the TRB was fragile, with more than half of the area (57.27%) dominated by very heavy and heavy grades of ecological vulnerability, and 28.40% of the area had potential and light grades of ecological vulnerability. The light grade of ecological vulnerability was distributed in the northern regions (Aksu River and Weigan River catchments) and western regions (Kashgar River and Yarkant River catchments), while the heavy grade was located in the southern regions (Kunlun Mountains and Qarqan River catchments) and the Mainstream catchment. The ecosystems in the western and northern regions were less vulnerable than those in the southern and eastern regions. From 2000 to 2017, the overall improvement in ecological vulnerability in the whole TRB showed that the areas with great ecological improvement increased by 46.11%, while the areas with ecological degradation decreased by 9.64%. The vegetation cover and potential evapotranspiration (PET) were the obvious driving factors, explaining 57.56% and 21.55% of the changes in ecological vulnerability across the TRB, respectively. In terms of ecological vulnerability grade changes, obvious spatial differences were observed in the upper, middle, and lower reaches of the TRB due to the different vegetation and hydrothermal conditions. The alpine source region of the TRB showed obvious ecological improvement due to increased precipitation and temperature, but the alpine meadow of the Kaidu River catchment in the Middle Tianshan Mountains experienced degradation associated with overgrazing and local drought. The improved agricultural management technologies had positive effects on farmland ecological improvement, while the desert vegetation in oasis-desert ecotones showed a decreasing trend as a result of cropland reclamation and intensive drought. The desert riparian vegetation in the lower reaches of the Tarim River was greatly improved due to the implementation of the EWDP, which has been active for tens of years. These results provide comprehensive knowledge about ecological processes and mechanisms in the whole TRB and help to develop environmental restoration measures based on different ecological vulnerability grades in each sub-catchment.

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Climate change impacts on the streamflow of Zarrineh River, Iran
Farhad YAZDANDOOST, Sogol MORADIAN
Journal of Arid Land    2021, 13 (9): 891-904.   DOI: 10.1007/s40333-021-0091-4
Abstract87)   HTML8)    PDF (1733KB)(300)      

Zarrineh River is located in the northwest of Iran, providing more than 40% of the total inflow into the Lake Urmia that is one of the largest saltwater lakes on the earth. Lake Urmia is a highly endangered ecosystem on the brink of desiccation. This paper studied the impacts of climate change on the streamflow of Zarrineh River. The streamflow was simulated and projected for the period 1992-2050 through seven CMIP5 (coupled model intercomparison project phase 5) data series (namely, BCC-CSM1-1, BNU-ESM, CSIRO-Mk3-6-0, GFDL-ESM2G, IPSL-CM5A-LR, MIROC-ESM and MIROC-ESM-CHEM) under RCP2.6 (RCP, representative concentration pathways) and RCP8.5. The model data series were statistically downscaled and bias corrected using an artificial neural network (ANN) technique and a Gamma based quantile mapping bias correction method. The best model (CSIRO-Mk3-6-0) was chosen by the TOPSIS (technique for order of preference by similarity to ideal solution) method from seven CMIP5 models based on statistical indices. For simulation of streamflow, a rainfall-runoff model, the hydrologiska byrans vattenavdelning (HBV-Light) model, was utilized. Results on hydro-climatological changes in Zarrineh River basin showed that the mean daily precipitation is expected to decrease from 0.94 and 0.96 mm in 2015 to 0.65 and 0.68 mm in 2050 under RCP2.6 and RCP8.5, respectively. In the case of temperature, the numbers change from 12.33°C and 12.37°C in 2015 to 14.28°C and 14.32°C in 2050. Corresponding to these climate scenarios, this study projected a decrease of the annual streamflow of Zarrineh River by half from 2015 to 2050 as the results of climatic changes will lead to a decrease in the annual streamflow of Zarrineh River from 59.49 m3/s in 2015 to 22.61 and 23.19 m3/s in 2050. The finding is of important meaning for water resources planning purposes, management programs and strategies of the Lake's endangered ecosystem.

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Effects of restoration modes on the spatial distribution of soil physical properties after land consolidation: a multifractal analysis
KE Zengming, LIU Xiaoli, MA Lihui, TU Wen, FENG Zhe, JIAO Feng, WANG Zhanli
Journal of Arid Land    2021, 13 (12): 1201-1214.   DOI: 10.1007/s40333-021-0027-z
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Soil physical properties (SPP) are considered to be important indices that reflect soil structure, hydrological conditions and soil quality. It is of substantial interest to study the spatial distribution of SPP owing to the high spatial variability caused by land consolidation under various land restoration modes in excavated farmland in the loess hilly area of China. In our study, three land restoration modes were selected including natural restoration land (NR), alfalfa land (AL) and maize land (ML). Soil texture composition, including the contents of clay, silt and sand, field capacity (FC), saturated conductivity (Ks) and bulk density (BD) were determined using a multifractal analysis. SPP were found to possess variable characteristics, although land consolidation destroyed the soil structure and decreased the spatial autocorrelation. Furthermore, SPP varied with land restoration and could be illustrated by the multifractal parameters of D1, ∆D, ∆α and ∆f in different modes of land restoration. Owing to multiple compaction from large machinery in the surface soil, soil particles were fine-grained and increased the spatial variability in soil texture composition under all the land restoration modes. Plough numbers and vegetative root characteristics had the most significant impacts on the improvement in SPP, which resulted in the best spatial distribution characteristics of SPP found in ML compared with those in AL and NR. In addition, compared with ML, ∆α values of NR and AL were 4.9- and 3.0-fold that of FC, respectively, and ∆α values of NR and AL were 2.3- and 1.5-fold higher than those of Ks, respectively. These results indicate that SPP can be rapidly improved by increasing plough numbers and planting vegetation types after land consolidation. Thus, we conclude that ML is an optimal land restoration mode that results in favorable conditions to rapidly improve SPP.

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Spatiotemporal variations of evapotranspiration and reference crop water requirement over 1957-2016 in Iran based on CRU TS gridded dataset
Brian COLLINS, Hadi RAMEZANI ETEDALI, Ameneh TAVAKOL, Abbas KAVIANI
Journal of Arid Land    2021, 13 (8): 858-878.   DOI: 10.1007/s40333-021-0103-4
Abstract78)   HTML9)    PDF (6486KB)(322)      

Agriculture needs to produce more food to feed the growing population in the 21st century. It makes the reference crop water requirement (WREQ) a major challenge especially in regions with limited water and high water demand. Iran, with large climatic variability, is experiencing a serious water crisis due to limited water resources and inefficient agriculture. In order to overcome the issue of uneven distribution of weather stations, gridded Climatic Research Unit (CRU) data was applied to analyze the changes in potential evapotranspiration (PET), effective precipitation (EFFPRE) and WREQ. Validation of data using in situ observation showed an acceptable performance of CRU in Iran. Changes in PET, EFFPRE and WREQ were analyzed in two 30-a periods 1957-1986 and 1987-2016. Comparing two periods showed an increase in PET and WREQ in regions extended from the southwest to northeast and a decrease in the southeast, more significant in summer and spring. However, EFFPRE decreased in the southeast, northeast, and northwest, especially in winter and spring. Analysis of annual trends revealed an upward trend in PET (14.32 mm/decade) and WREQ (25.50 mm/decade), but a downward trend in EFFPRE (-11.8 mm/decade) over the second period. Changes in PET, EFFPRE and WREQ in winter have the impact on the annual trend. Among climate variables, WREQ showed a significant correlation (r=0.59) with minimum temperature. The increase in WREQ and decrease in EFFPRE would exacerbate the agricultural water crisis in Iran. With all changes in PET and WREQ, immediate actions are needed to address the challenges in agriculture and adapt to the changing climate.

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Spatiotemporal variation of forest land and its driving factors in the agropastoral ecotone of northern China
WANG Shiqing, TAO Zefu, SUN Piling, CHEN Sijia, SUN Huiying, LI Nan
Journal of Arid Land    2022, 14 (1): 1-13.   DOI: 10.1007/s40333-022-0001-4
Abstract72)   HTML15)    PDF (1545KB)(112)      

As an important natural resource, forest land plays a key role in the maintenance of ecological security. However, variations of forest land in the agropastoral ecotone of northern China (AENC) have attracted little attention. Taking the AENC as an example and based on remote-sensing images from 2000, 2010 to 2020, we explored the spatiotemporal variation of forest land and its driving factors using the land-use transfer matrix, spatial autocorrelation analysis and spatial error model. The results showed that from 2000 to 2020, the total area of forest land in the AENC increased from 75,547.52 to 77,359.96 km2 and the changes were dominated by the transformations among forest land, grassland and cropland, which occurred mainly in areas with the elevation of 500-2000 m and slope of 15°-25°. There was obvious spatial agglomeration of forest land in the AENC from 2000 to 2020, with hot spots of forest land gathered in the southern marginal areas of the Yanshan Mountains and the low mountainous and hilly areas of the Loess Plateau. The sub-hot spots around hot spots moved southward, the sub-cold spots spread to the surrounding areas and the cold spots disappeared. The spatiotemporal variation of forest land resulted from the interactions of natural environment, socioeconomic and policy factors from 2000 to 2020. The variables of average annual precipitation, slope, terrain relief, ecological conversion program and afforestation policy for barren mountains affected the spatial pattern of forest land positively, while those of annual average temperature, slope and road network density influenced it negatively.

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Response of C:N:P in the plant-soil system and stoichiometric homeostasis of Nitraria tangutorum leaves in the oasis-desert ecotone, Northwest China
WEI Yajuan, DANG Xiaohong, WANG Ji, GAO Junliang, GAO Yan
Journal of Arid Land    2021, 13 (9): 934-946.   DOI: 10.1007/s40333-021-0019-z
Abstract70)   HTML6)    PDF (697KB)(65)      

Nitraria tangutorum nebkhas are widely distributed in the arid and semi-arid desert areas of China. The formation and development of N. tangutorum nebkhas are the result of the interaction between vegetation and the surrounding environment in the process of community succession. Different successional stages of N. tangutorum nebkhas result in differences in the community structure and composition, thereby strongly affecting the distribution of soil nutrients and ecosystem stability. However, the ecological stoichiometry of N. tangutorum nebkhas in different successional stages remains poorly understood. Understanding the stoichiometric homeostasis of N. tangutorum could provide insights into its adaptability to the arid and semi-arid desert environments. Therefore, we analyzed the stoichiometric characteristics of N. tangutorum in four successional stages, i.e., rudimental, developing, stabilizing, and degrading stages using a homeostasis model in an oasis-desert ecotone of Northwest China. The results showed that soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) contents and their ratios in the 0-100 cm soil depth were significantly lower than the averages at regional and global scales and were weakly influenced by successional stages in the oasis-desert ecotone. TN and TP contents and C:N:P in the soil showed similar trends. Total carbon (TC) and TN contents in leaves were 450.69-481.07 and 19.72-29.35 g/kg, respectively, indicating that leaves of N. tangutorum shrubs had a high storage capacity for C and N. Leaf TC and TN contents and N:P ratio increased from the rudimental stage to the stabilizing stage and then decreased in the degrading stage, while the reverse trend was found for leaf C:N. Leaf TP content decreased from the rudimental stage to the degrading stage and changed significantly in late successional stages. N:P ratio was above the theoretical limit of 14, indicating that the growth of N. tangutorum shrubs was limited by P during successional stages. Leaf N, P, and N:P homeostasis in four successional stages was identified as ''strictly homeostasis''. Redundancy analysis (RDA) revealed that soil acidity (pH) and the maximum water holding capacity were the main factors affecting C:N:P stoichiometric characteristics in N. tangutorum leaves. Our study demonstrated that N. tangutorum with a high degree of stoichiometric homeostasis could better cope with the arid desert environment.

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Modeling and analyzing supply-demand relationships of water resources in Xinjiang from a perspective of ecosystem services
LI Feng, LI Yaoming, ZHOU Xuewen, YIN Zun, LIU Tie, XIN Qinchuan
Journal of Arid Land    2022, 14 (2): 115-138.   DOI: 10.1007/s40333-022-0059-z
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Water shortage is one bottleneck that limits economic and social developments in arid and semi-arid areas. As the impacts of climate change and human disturbance intensify across time, uncertainties in both water resource supplies and demands increase in arid and semi-arid areas. Taking a typical arid region in China, Xinjiang Uygur Autonomous Region, as an example, water yield depth (WYD) and water utilization depth (WUD) from 2002 to 2018 were simulated using the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) model and socioeconomic data. The supply-demand relationships of water resources were analyzed using the ecosystem service indices including water supply-demand difference (WSDD) and water supply rate (WSR). The internal factors in changes of WYD and WUD were explored using the controlled variable method. The results show that the supply- demand relationships of water resources in Xinjiang were in a slight deficit, but the deficit was alleviated due to increased precipitation and decreased WUD of irrigation. WYD generally experienced an increasing trend, and significant increase mainly occurred in the oasis areas surrounding both the Junggar Basin and Tarim Basin. WUD had a downward trend with a decline of 20.70%, especially in oasis areas. Water resources in most areas of Xinjiang were fully utilized and the utilization efficiency of water resources increased. The water yield module in the InVEST model was calibrated and validated using gauging station data in Xinjiang, and the result shows that the use of satellite-based water storage data helped to decrease the bias error of the InVEST model by 0.69×108 m3. This study analyzed water resource supplies and demands from a perspective of ecosystem services, which expanded the scope of the application of ecosystem services and increased the research perspective of water resource evaluation. The results could provide guidance for water resource management such as spatial allocation and structural optimization of water resources in arid and semi-arid areas.

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Hydrochemical characteristics and evolution of groundwater in the dried-up river oasis of the Tarim Basin, Central Asia
WANG Wanrui, CHEN Yaning, WANG Weihua, XIA Zhenhua, LI Xiaoyang, Patient M KAYUMBA
Journal of Arid Land    2021, 13 (10): 977-994.   DOI: 10.1007/s40333-021-0086-1
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Intense human activities in arid areas have great impacts on groundwater hydrochemical cycling by causing groundwater salinization. The spatiotemporal distributions of groundwater hydrochemistry are crucial for studying groundwater salt migration, and also vital to understand hydrological and hydrogeochemical processes of groundwater in arid inland oasis areas. However, due to constraints posed by the paucity of observation data and intense human activities, these processes are not well known in the dried-up river oases of arid areas. Here, we examined spatiotemporal variations and evolution of groundwater hydrochemistry using data from 199 water samples collected in the Wei-Ku Oasis, a typical arid inland oasis in Tarim Basin of Central Asia. As findings, groundwater hydrochemistry showed a spatiotemporal dynamic, while its spatial distribution was complex. TDS and δ18O of river water in the upstream increased from west to east, whereas ion concentrations of shallow groundwater increased from northwest to southeast. Higher TDS was detected in spring for shallow groundwater and in summer for middle groundwater. Pronounced spatiotemporal heterogeneity demonstrated the impacts of geogenic, climatic, and anthropogenic conditions. For that, hydrochemical evolution of phreatic groundwater was primarily controlled by rock dominance and evaporation-crystallization process. Agricultural irrigation and drainage, land cover change, and groundwater extraction reshaped the spatiotemporal patterns of groundwater hydrochemistry. Groundwater overexploitation altered the leaking direction between the aquifers, causing the interaction between saltwater and freshwater and the deterioration of groundwater environment. These findings could provide an insight into groundwater salt migration under human activities, and hence be significant in groundwater quality management in arid inland oasis areas.

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Assessing the response of dryland barley yield to climate variability in semi-arid regions, Iran
Mohammad KHEIRI, Jafar KAMBOUZIA, Reza DEIHIMFARD, Saghi M MOGHADDAM, Seyran ANVARI
Journal of Arid Land    2021, 13 (9): 905-917.   DOI: 10.1007/s40333-021-0017-1
Abstract63)   HTML7)    PDF (733KB)(217)      

Precipitation and temperature are the most abiotic factors that greatly impact the yield of crop, particularly in dryland. Barley, as the main cereal is predominantly cultivated in dryland and the livelihood of smallholders depends on the production of this crop, particularly in arid and semi-arid regions. This study aimed to investigate the response of the grain yield of dryland barley to temperature and precipitation variations at annual, seasonal and monthly scales in seven counties of East and West Azerbaijan provinces in northwestern Iran during 1991-2010. Humidity index (HI) was calculated and its relationship with dryland barley yield was evaluated at annual and monthly scales. The results showed that the minimum, maximum and mean temperatures increased by 0.19°C/a, 0.11°C/a and 0.10°C/a, respectively, while annual precipitation decreased by 0.80 mm/a during 1991-2010. Climate in study area has become drier by 0.22/a in annual HI during the study period. Negative effects of increasing temperature on the grain yield of dryland barley were more severe than the positive effects of increasing precipitation. Besides, weather variations in April and May were related more to the grain yield of dryland barley than those in other months. The grain yield of dryland barley was more drastically affected by the variation of annual minimum temperature comparing with other weather variables. Furthermore, our findings illustrated that the grain yield of dryland barley increased by 0.01 t/hm2 for each unit increase in annual HI during 1991-2010. Finally, any increase in the monthly HI led to crop yield improvement in the study area, particularly in the drier counties, i.e., Myaneh, Tabriz and Khoy in Iran.

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Effects of climate change and land use/cover change on the volume of the Qinghai Lake in China
WANG Hongwei, QI Yuan, LIAN Xihong, ZHANG Jinlong, YANG Rui, ZHANG Meiting
Journal of Arid Land    2022, 14 (3): 245-261.   DOI: 10.1007/s40333-022-0062-4
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Qinghai Lake is the largest saline lake in China. The change in the lake volume is an indicator of the variation in water resources and their response to climate change on the Qinghai-Tibetan Plateau (QTP) in China. The present study quantitatively evaluated the effects of climate change and land use/cover change (LUCC) on the lake volume of the Qinghai Lake in China from 1958 to 2018, which is crucial for water resources management in the Qinghai Lake Basin. To explore the effects of climate change and LUCC on the Qinghai Lake volume, we analyzed the lake level observation data and multi-period land use/land cover (LULC) data by using an improved lake volume estimation method and Integrated Valuation of Ecosystem Services and Trade-offs (InVEST) model. Our results showed that the lake level decreased at the rate of 0.08 m/a from 1958 to 2004 and increased at the rate of 0.16 m/a from 2004 to 2018. The lake volume decreased by 105.40×108 m3 from 1958 to 2004, with the rate of 2.24×108 m3/a, whereas it increased by 74.02×108 m3 from 2004 to 2018, with the rate of 4.66×108 m3/a. Further, the climate of the Qinghai Lake Basin changed from warm-dry to warm-humid. From 1958 to 2018, the increase in precipitation and the decrease in evaporation controlled the change of the lake volume, which were the main climatic factors affecting the lake volume change. From 1977 to 2018, the measured water yield showed an "increase-decrease-increase" fluctuation in the Qinghai Lake Basin. The effects of climate change and LUCC on the measured water yield were obviously different. From 1977 to 2018, the contribution rate of LUCC was -0.76% and that of climate change was 100.76%; the corresponding rates were 8.57% and 91.43% from 1977 to 2004, respectively, and -4.25% and 104.25% from 2004 to 2018, respectively. Quantitative analysis of the effects and contribution rates of climate change and LUCC on the Qinghai Lake volume revealed the scientific significance of climate change and LUCC, as well as their individual and combined effects in the Qinghai Lake Basin and on the QTP. This study can contribute to the water resources management and regional sustainable development of the Qinghai Lake Basin.

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Effects of different ridge-furrow mulching systems on yield and water use efficiency of summer maize in the Loess Plateau of China
CHEN Pengpeng, GU Xiaobo, LI Yuannong, QIAO Linran, LI Yupeng, FANG Heng, YIN Minhua, ZHOU Changming
Journal of Arid Land    2021, 13 (9): 947-961.   DOI: 10.1007/s40333-021-0081-6
Abstract57)   HTML3)    PDF (950KB)(176)      

Ridge-furrow film mulching has been proven to be an effective water-saving and yield-improving planting pattern in arid and semi-arid regions. Drought is the main factor limiting the local agricultural production in the Loess Plateau of China. In this study, we tried to select a suitable ridge-furrow mulching system to improve this situation. A two-year field experiment of summer maize (Zea mays L.) during the growing seasons of 2017 and 2018 was conducted to systematically analyze the effects of flat planting with no film mulching (CK), ridge-furrow with ridges mulching and furrows bare (RFM), and double ridges and furrows full mulching (DRFFM) on soil temperature, soil water storage (SWS), root growth, aboveground dry matter, water use efficiency (WUE), and grain yield. Both RFM and DRFFM significantly increased soil temperature in ridges, while soil temperature in furrows for RFM and DRFFM was similar to that for CK. The largest SWS was observed in DRFFM, followed by RFM and CK, with significant differences among them. SWS was lower in ridges than in furrows for RFM. DRFFM treatment kept soil water in ridges, resulting in higher SWS in ridges than in furrows after a period of no water input. Across the two growing seasons, compared with CK, RFM increased root mass by 10.2% and 19.3% at the jointing and filling stages, respectively, and DRFFM increased root mass by 7.9% at the jointing stage but decreased root mass by 6.0% at the filling stage. Over the two growing seasons, root length at the jointing and filling stages was respectively increased by 75.4% and 58.7% in DRFFM, and 20.6% and 30.2% in RFM. Relative to the jointing stage, the increased proportions of root mass and length at the filling stage were respectively 42.8% and 94.9% in DRFFM, 63.2% and 115.1% in CK, and 76.7% and 132.1% in RFM, over the two growing seasons, showing that DRFFM slowed down root growth while RFM promoted root growth at the later growth stages. DRFFM treatment increased root mass and root length in ridges and decreased them in 0-30 cm soil layer, while RFM increased them in 0-30 cm soil layer. Compared with CK, DRFFM decreased aboveground dry matter while RFM increased it. Evapotranspiration was reduced by 9.8% and 7.1% in DRFFM and RFM, respectively, across the two growing seasons. Grain yield was decreased by 14.3% in DRFFM and increased by 13.6% in RFM compared with CK over the two growing seasons. WUE in CK was non-significantly 6.8% higher than that in DRFFM and significantly 22.5% lower than that in RFM across the two growing seasons. Thus, RFM planting pattern is recommended as a viable water-saving option for summer maize in the Loess Plateau of China.

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Spatiotemporal changes of eco-environmental quality based on remote sensing-based ecological index in the Hotan Oasis, Xinjiang
YAO Kaixuan, Abudureheman HALIKE, CHEN Limei, WEI Qianqian
Journal of Arid Land    2022, 14 (3): 262-283.   DOI: 10.1007/s40333-022-0011-2
Abstract56)   HTML12)    PDF (4002KB)(159)      

The rapid economic development that the Hotan Oasis in Xinjiang Uygur Autonomous Region, China has undergone in recent years may face some challenges in its ecological environment. Therefore, an analysis of the spatiotemporal changes in ecological environment of the Hotan Oasis is important for its sustainable development. First, we constructed an improved remote sensing-based ecological index (RSEI) in 1990, 1995, 2000, 2005, 2010, 2015 and 2020 on the Google Earth Engine (GEE) platform and implemented change detection for their spatial distribution. Second, we performed a spatial autocorrelation analysis on RSEI distribution map and used land-use and land-cover change (LUCC) data to analyze the reasons of RSEI changes. Finally, we investigated the applicability of improved RSEI to arid area. The results showed that mean of RSEI rose from 0.41 to 0.50, showing a slight upward trend. During the 30-a period, 2.66% of the regions improved significantly, 10.74% improved moderately and 32.21% improved slightly, respectively. The global Moran's I were 0.891, 0.889, 0.847 and 0.777 for 1990, 2000, 2010 and 2020, respectively, and the local indicators of spatial autocorrelation (LISA) distribution map showed that the high-high cluster was mainly distributed in the central part of the Hotan Oasis, and the low-low cluster was mainly distributed in the outer edge of the oasis. RSEI at the periphery of the oasis changes from low to high with time, with the fragmentation of RSEI distribution within the oasis increasing. Its distribution and changes are predominantly driven by anthropologic factors, including the expansion of artificial oasis into the desert, the replacement of desert ecosystems by farmland ecosystems, and the increase in the distribution of impervious surfaces. The improved RSEI can reflect the eco-environmental quality effectively of the oasis in arid area with relatively high applicability. The high efficiency exhibited with this approach makes it convenient for rapid, high frequency and macroscopic monitoring of eco-environmental quality in study area.

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Seasonal dynamics of soil water content in the typical vegetation and its response to precipitation in a semi-arid area of Chinese Loess Plateau
ZHOU Tairan, HAN Chun, QIAO Linjie, REN Chaojie, WEN Tao, ZHAO Changming
Journal of Arid Land    2021, 13 (10): 1015-1025.   DOI: 10.1007/s40333-021-0021-5
Abstract51)   HTML4)    PDF (902KB)(197)      

Soil water content is a key limiting factor for vegetation growth in the semi-arid area of Chinese Loess Plateau and precipitation is the main source of soil water content in this area. To further understand the impact of vegetation types and environmental factors such as precipitation on soil water content, we continuously monitored the seasonal dynamics in soil water content in four plots (natural grassland, Caragana korshinskii, Armeniaca sibirica and Pinus tabulaeformis) in Chinese Loess Plateau. The results show that the amplitude of soil water content fluctuation decreases with an increase in soil depth, showing obvious seasonal variations. Soil water content of artificial vegetation was found to be significantly lower than that of natural grassland, and most precipitation events have difficulty replenishing soil water content below a depth of 40 cm. Spring and autumn are the key seasons for replenishment of soil water by precipitation. Changes in soil water content are affected by precipitation, vegetation types, soil evaporation and other factors. The interception effect of vegetation on precipitation and the demand for water consumption by transpiration are the key factors affecting the efficiency of soil water replenishment by precipitation in this area. Due to artificial vegetation plantation in this area, soil will face a water deficit crisis in the future.

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Succession of soil bacterial and fungal communities of Caragana korshinskii plantation in a typical agro-pastoral ecotone in northern China over a 50-a period
MA Gailing, GOU Qianqian, WANG Guohua, QU Jianjun
Journal of Arid Land    2021, 13 (10): 1071-1086.   DOI: 10.1007/s40333-021-0022-4
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Bacterial and fungal communities play critical roles in reestablishing vegetation structure, function and biodiversity in ecosystem restoration in arid and semi-arid areas. However, the long-term successional changes in bacterial and fungal communities that occur with artificial vegetation development are not fully understood. In this study, we investigated the successional changes in bacterial and fungal communities in Caragana korshinskii Kom. plantation over a period of 50 a (6, 12, 18, 40 and 50 a) and their relationships with key soil environmental factors in a typical agro-pastoral ecotone, northern China. The results showed that bacterial and fungal diversities (α- and β-diversity) were significantly affected by plantation age; moreover, the change in fungal community was more evident than that in bacterial community. Soil samples from 12 a plantation had the highest (P<0.05) bacterial and fungal α-diversity (i.e., abundance-based coverage estimator (ACE) and Chao1 index) at 0-10 cm depth compared with other samples. However, soil samples from plantation at the late recovery stage (40-50 a) had the highest α-diversity at 10-20 cm depth. Soil bacterial community was not significantly affected by plantation age at the genus level; but, soil fungal community was significantly affected at the genus level. Overall, Mortierella and Chaetomium were the dominant genera at natural recovery stage (0 a); Inocybe was the dominant genus at the early recovery stage (6-12 a); Inocybe and Mortierella were the dominant genera at the mid-recovery stage (12-40 a); And Mortierella, Cladosporium and Humicola were the dominant genera at the late recovery stage (40-50 a). Redundancy analysis (RDA) showed that β-glucosidase activity, total nitrogen and soil organic carbon were closely associated with bacterial community composition, while alkaline phosphatase, urease activity and total nitrogen were associated with fungal community composition, indicating that changes in enzyme activity and soil nutrients were the most important determinants of dominant genera. Furthermore, pathogenic microorganisms (Cladosporium and Humicola) were dominant in soils from 40-50 a plantation, which may affect plant growth, resulting in the decline of C. korshinskii plantation. Overall, the findings of this study improve the understanding of ecological patterns of bacterial and fungal communities in artificial vegetation and provide an important scientific basis for comprehensive ecological restoration management in arid and semi-arid areas.

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Response of ecosystem service value to land use/cover change in the northern slope economic belt of the Tianshan Mountains, Xinjiang, China
SUN Chen, MA Yonggang, GONG Lu
Journal of Arid Land    2021, 13 (10): 1026-1040.   DOI: 10.1007/s40333-021-0082-5
Abstract47)   HTML6)    PDF (835KB)(58)      

Land use/cover change (LUCC) is becoming more and more frequent and extensive as a result of human activities, and is expected to have a major impact on human welfare by altering ecosystem service value (ESV). In this study, we utilized remote sensing images and statistical data to explore the spatial-temporal changes of land use/cover types and ESV in the northern slope economic belt of the Tianshan Mountains in Xinjiang Uygur Autonomous Region, China from 1975 to 2018. During the study period, LUCC in the study region varied significantly. Except grassland and unused land, all the other land use/cover types (cultivated land, forestland, waterbody, and construction land) increased in areas. From 1975 to 2018, the spatial-temporal variations in ESV were also pronounced. The total ESV decreased by 4.00×108 CNY, which was primarily due to the reductions in the areas of grassland and unused land. Waterbody had a much higher ESV than the other land use/cover types. Ultimately, understanding the impact of LUCC on ESV and the interactions among ESV of different land use/cover types will help improve existing land use policies and provide scientific basis for developing new conservation strategies for ecologically fragile areas.

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Effect of nitrogen and phosphorus addition on leaf nutrient concentrations and nutrient resorption efficiency of two dominant alpine grass species
LIU Yalan, LI Lei, LI Xiangyi, YUE Zewei, LIU Bo
Journal of Arid Land    2021, 13 (10): 1041-1053.   DOI: 10.1007/s40333-021-0080-7
Abstract47)   HTML4)    PDF (605KB)(208)      

Nitrogen (N) and phosphorus (P) are two essential nutrients that determine plant growth and many nutrient cycling processes. Increasing N and P deposition is an important driver of ecosystem changes. However, in contrast to numerous studies about the impacts of nutrient addition on forests and temperate grasslands, how plant foliar stoichiometry and nutrient resorption respond to N and P addition in alpine grasslands is poorly understood. Therefore, we conducted an N and P addition experiment (involving control, N addition, P addition, and N+P addition) in an alpine grassland on Kunlun Mountains (Xinjiang Uygur Autonomous Region, China) in 2016 and 2017 to investigate the changes in leaf nutrient concentrations (i.e., leaf N, Leaf P, and leaf N:P ratio) and nutrient resorption efficiency of Seriphidium rhodanthum and Stipa capillata, which are dominant species in this grassland. Results showed that N addition has significant effects on soil inorganic N (NO3--N and NH4+-N) and leaf N of both species in the study periods. Compared with green leaves, leaf nutrient concentrations and nutrient resorption efficiency in senesced leaves of S. rhodanthum was more sensitive to N addition, whereas N addition influenced leaf N and leaf N:P ratio in green and senesced leaves of S. capillata. N addition did not influence N resorption efficiency of the two species. P addition and N+P addition significantly improved leaf P and had a negative effect on P resorption efficiency of the two species in the study period. These influences on plants can be explained by increasing P availability. The present results illustrated that the two species are more sensitive to P addition than N addition, which implies that P is the major limiting factor in the studied alpine grassland ecosystem. In addition, an interactive effect of N+P addition was only discernable with respect to soil availability, but did not affect plants. Therefore, exploring how nutrient characteristics and resorption response to N and P addition in the alpine grassland is important to understand nutrient use strategy of plants in terrestrial ecosystems.

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Characterizing the spatiotemporal variations of evapotranspiration and aridity index in mid-western China from 2001 to 2016
MU Le, LU Yixiao, LIU Minguo, YANG Huimin, FENG Qisheng
Journal of Arid Land    2021, 13 (12): 1230-1243.   DOI: 10.1007/s40333-021-0087-0
Abstract45)   HTML17)    PDF (1622KB)(93)      

Mid-western China is one of the most sensitive and fragile areas on the Earth. Evapotranspiration (ET) is a key part of hydrological cycle in these areas and is affected by both global climate change and human activities. The dynamic changes in ET and potential evapotranspiration (PET), which can reflect water consumption and demand, are still unclear, and there is a lack of predictive capacity on drought severity. In this study, we used global MODIS (moderate-resolution imaging spectroradiometer) terrestrial ET (MOD16) products, Morlet wavelet analysis, and simple linear regression to investigate the spatiotemporal variations of ET, PET, reference ET (ET0), and aridity index (AI) in mid-western pastoral regions of China (including Gansu Province, Qinghai Province, Ningxia Hui Autonomous Region, and part of Inner Mongolia Autonomous Region) from 2001 to 2016. The results showed that the overall ET gradually increased from east to southwest in the study area. Actual ET showed an increasing trend, whereas PET tended to decrease from 2001 to 2016. The change in ET was affected by vegetation types. During the study period, the average annual ET0 and AI tended to decrease. At the monthly scale within a year, AI value decreased from January to July and then increased. The interannual variations of ET0 and AI showed periodicity with a main period of 14 a, and two other periodicities of 11 and 5 a. This study showed that in recent years, drought in these pastoral regions of mid-western China has been alleviated. Therefore, it is foreseeable that the demand for irrigation water for agricultural production in these regions will decrease.

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Temporal and spatial variations of net primary productivity and its response to groundwater of a typical oasis in the Tarim Basin, China
SUN Lingxiao, YU Yang, GAO Yuting, ZHANG Haiyan, YU Xiang, HE Jing, WANG Dagang, Ireneusz MALIK, Malgorzata WISTUBA, YU Ruide
Journal of Arid Land    2021, 13 (11): 1142-1154.   DOI: 10.1007/s40333-021-0088-z
Abstract43)   HTML8)    PDF (1908KB)(139)      

Net primary productivity (NPP) of the vegetation in an oasis can reflect the productivity capacity of a plant community under natural environmental conditions. Owing to the extreme arid climate conditions and scarce precipitation in the arid oasis regions, groundwater plays a key role in restricting the development of the vegetation. The Qira Oasis is located on the southern margin of the Taklimakan Desert (Tarim Basin, China) that is one of the most vulnerable regions regarding vegetation growth and water scarcity in the world. Based on remote sensing images of the Qira Oasis and daily meteorological data measured by the ground stations during the period 2006-2019, this study analyzed the temporal and spatial patterns of NPP in the oasis as well as its relation with the variation of groundwater depth using a modified Carnegie Ames Stanford Approach (CASA) model. At the spatial scale, NPP of the vegetation decreased from the interior of the Qira Oasis to the margin; at the temporal scale, NPP of the vegetation in the oasis fluctuated significantly (ranging from 29.80 to 50.07 g C/(m2•month)) but generally showed an increasing trend, with the average increase rate of 0.07 g C/(m2•month). The regions with decreasing NPP occupied 64% of the total area of the oasis. During the study period, NPP of both farmland and grassland showed an increasing trend, while that of forest showed a decreasing trend. The depth of groundwater was deep in the south of the oasis and shallow in the north, showing a gradual increasing trend from south to north. Groundwater, as one of the key factors in the surface change and evolution of the arid oasis, determines the succession direction of the vegetation in the Qira Oasis. With the increase of groundwater depth, grassland coverage and vegetation NPP decreased. During the period 2008-2015, with the recovery of groundwater level, NPP values of all types of vegetation with different coverages increased. This study will provide a scientific basis for the rational utilization and sustainable management of groundwater resources in the oasis.

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Disturbance of plateau zokor-made mound stimulates plant community regeneration in the Qinghai-Tibetan Plateau, China
XIANG Zeyu, Arvind BHATT, TANG Zhongbin, PENG Yansong, WU Weifeng, ZHANG Jiaxin, WANG Jingxuan, David GALLACHER, ZHOU Saixia
Journal of Arid Land    2021, 13 (10): 1054-1070.   DOI: 10.1007/s40333-021-0020-6
Abstract42)   HTML8)    PDF (3110KB)(259)      

Mounds constructed by plateau zokors, which is widely distributed in alpine meadows significantly modified plant community structure. However, the variations of plant community structure under the disturbance of plateau zokor-made mound are less concerned. Therefore, we investigated the responses of plant community on zokor-made mound of different years (1 a and 3-4 a), and compared with undisturbed sites (no mound) in an alpine meadow in the eastern Qinghai-Tibetan Plateau (QTP), China. Species richness, coverage and Simpson diversity index were all significantly reduced by the presence of zokor-made mound, but plant heights were significantly increased, particularly in grasses and sedges. Several perennial forage species showed an increased importance value and niche breadth, including Koeleria macrantha, Elymus nutans and Poa pratensis. The effect of zokor-made mound on niche overlap showed that more intense interspecific competition produced a greater utilization of environmental resources. And this interspecific niche overlap was strengthened as succession progressed. The bare mound created by zokor burrowing activities provided a colonizing opportunity for non-dominant forage species, resulting in abundant plant species and plant diversity during the succession period. We concluded that presence of zokor-made mound was conducive to regeneration and vitality of plant community in alpine meadows, thus improving their resilience to anthropogenic stress.

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Two-dimensional hydrodynamic robust numerical model of soil erosion based on slopes and river basins
KANG Yongde, HUANG Miansong, HOU Jingming, TONG Yu, PAN Zhanpeng
Journal of Arid Land    2021, 13 (10): 995-1014.   DOI: 10.1007/s40333-021-0085-2
Abstract41)   HTML7)    PDF (1945KB)(177)      

Erosion is an important issue in soil science and is related to many environmental problems, such as soil erosion and sediment transport. Establishing a simulation model suitable for soil erosion prediction is of great significance not only to accurately predict the process of soil separation by runoff, but also improve the physical model of soil erosion. In this study, we develop a graphic processing unit (GPU)-based numerical model that combines two-dimensional (2D) hydrodynamic and Green-Ampt (G-A) infiltration modelling to simulate soil erosion. A Godunov-type scheme on a uniform and structured square grid is then generated to solve the relevant shallow water equations (SWEs). The highlight of this study is the use of GPU-based acceleration technology to enable numerical models to simulate slope and watershed erosion in an efficient and high-resolution manner. The results show that the hydrodynamic model performs well in simulating soil erosion process. Soil erosion is studied by conducting calculation verification at the slope and basin scales. The first case involves simulating soil erosion process of a slope surface under indoor artificial rainfall conditions from 0 to 1000 s, and there is a good agreement between the simulated values and the measured values for the runoff velocity. The second case is a river basin experiment (Coquet River Basin) that involves watershed erosion. Simulations of the erosion depth change and erosion cumulative amount of the basin during a period of 1-40 h show an elevation difference of erosion at 0.5-3.0 m, especially during the period of 20-30 h. Nine cross sections in the basin are selected for simulation and the results reveal that the depth of erosion change value ranges from -0.86 to -2.79 m and the depth of deposition change value varies from 0.38 to 1.02 m. The findings indicate that the developed GPU-based hydrogeomorphological model can reproduce soil erosion processes. These results are valuable for rainfall runoff and soil erosion predictions on rilled hillslopes and river basins.

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Ecological environment quality evaluation of the Sahel region in Africa based on remote sensing ecological index
WU Shupu, GAO Xin, LEI Jiaqiang, ZHOU Na, GUO Zengkun, SHANG Baijun
Journal of Arid Land    2022, 14 (1): 14-33.   DOI: 10.1007/s40333-022-0057-1
Abstract40)   HTML9)    PDF (2139KB)(76)      

Long-term monitoring of the ecological environment changes is helpful for the protection of the ecological environment. Based on the ecological environment of the Sahel region in Africa, we established a remote sensing ecological index (RSEI) model for this region by combining dryness, moisture, greenness, and desertification indicators. Using the Moderate-resolution Imaging Spectroradiometer (MODIS) data in Google Earth Engine (GEE) platform, this study analyzed the ecological environment quality of the Sahel region during the period of 2001-2020. We used liner regression and fluctuation analysis methods to study the trend and fluctuation of RSEI, and utilized the stepwise regression approach to analyze the contribution of each indicator to the RSEI. Further, the correlation analysis was used to analyze the correlation between RSEI and precipitation, and Hurst index was applied to evaluate the change trend of RSEI in the future. The results show that RSEI of the Sahel region exhibited spatial heterogeneity. Specifically, it exhibited a decrease in gradient from south to north of the Sahel region. Moreover, RSEI in parts of the Sahel region presented non-zonal features. Different land-cover types demonstrated different RSEI values and changing trends. We found that RSEI and precipitation were positively correlated, suggesting that precipitation is the controlling factor of RSEI. The areas where RSEI values presented an increasing trend were slightly less than the areas where RSEI values presented a decreasing trend. In the Sahel region, the areas with the ecological environment characterized by continuous deterioration and continuous improvement accounted for 44.02% and 28.29% of the total study area, respectively, and the areas in which the ecological environment was changing from improvement to deterioration and from deterioration to improvement accounted for 12.42% and 15.26% of the whole area, respectively. In the face of the current ecological environment and future change trends of RSEI in the Sahel region, the research results provide a reference for the construction of the ''Green Great Wall'' (GGW) ecological environment project in Africa.

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Spatial variability of leaf wetness under different soil water conditions in rainfed jujube ( Ziziphus jujuba Mill.) in the loess hilly region, China
GAO Zhiyong, WANG Xing
Journal of Arid Land    2022, 14 (1): 70-81.   DOI: 10.1007/s40333-022-0003-2
Abstract39)   HTML7)    PDF (1421KB)(126)      

Leaf wetness provides a wide range of benefits not only to leaves, but also to ecosystems and communities. It regulates canopy eco-hydrological processes and drives spatial differences in hydrological flux. In spite of these functions, little remains known about the spatial distribution of leaf wetness under different soil water conditions. Leaf wetness measurements at the top (180 cm), middle (135 cm), and bottom (85 cm) of the canopy positions of rainfed jujube (Ziziphus jujuba Mill.) in the Chinese loess hilly region were obtained along with meteorological and soil water conditions during the growing seasons in 2019 and 2020. Under soil water non-deficit condition, the frequency of occurrence of leaf wetness was 5.45% higher at the top than at the middle and bottom of the canopy positions. The frequency of occurrence of leaf wetness at the top, middle and bottom of the canopy positions was over 80% at 17:00-18:00 (LST). However, the occurrence of leaf wetness at the top was earlier than those at the middle and bottom of the canopy positions. Correspondingly, leaf drying at the top was also latter than those at the middle and bottom of the canopy positions. Leaf wetness duration at the middle was similar to that at the bottom of the canopy position, but about 1.46-3.01 h less than that at the top. Under soil water deficit condition, the frequency of occurrence of leaf wetness (4.92%-45.45%) followed the order of top>middle>bottom of the canopy position. As the onset of leaf wetness was delayed, the onset of wet leaf drying was advanced and the leaf wetness duration was shortened. Leaf wetness duration at the top was linearly related (R2>0.70) to those at the middle and bottom of the canopy positions under different soil water conditions. In conclusion, the hydrological processes at canopy surfaces of rainfed jujube depended on the position of leaves, thus adjusting canopy structure to redistribute hydrological process is a way to meet the water need of jujube.

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Predicting of dust storm source by combining remote sensing, statistic-based predictive models and game theory in the Sistan watershed, southwestern Asia
Mahdi BOROUGHANI, Sima POURHASHEMI, Hamid GHOLAMI, Dimitris G KASKAOUTIS
Journal of Arid Land    2021, 13 (11): 1103-1121.   DOI: 10.1007/s40333-021-0023-3
Abstract37)   HTML9)    PDF (2110KB)(217)      

Dust storms in arid and desert areas affect radiation budget, air quality, visibility, enzymatic activities, agricultural products and human health. Due to increased drought and land use changes in recent years, the frequency of dust storms occurrence in Iran has been increased. This study aims to identify dust source areas in the Sistan watershed (Iran-Afghanistan borders)-an important regional source for dust storms in southwestern Asia, using remote sensing (RS) and bivariate statistical models. Furthermore, this study determines the relative importance of factors controlling dust emissions using frequency ratio (FR) and weights of evidence (WOE) models and interpretability of predictive models using game theory. For this purpose, we identified 211 dust sources in the study area and generated a dust source distribution map-inventory map-by dust source potential index based on RS data. In addition, spatial maps of topographic factors affecting dust source areas including soil, lithology, slope, Normalized difference vegetation index (NDVI), geomorphology and land use were prepared. The performance of two models (WOE and FR) was evaluated using the area under curve (AUC) of the receiver operating characteristic curve. The results showed that soil, geomorphology and slope exhibited the greatest influence in the dust source areas. The 55.3% (according to FR) and 62.6% (according to WOE) of the total area were classified as high and very high potential dust sources, while both models displayed acceptable accuracy with subsurface levels of 0.704 for FR and 0.751 for WOE, although they predict different fractions of dust potential classes. Based on Shapley additive explanations (SHAP), three factors, i.e., soil, slope and NDVI have the highest impact on the model's output. Overall, combination of statistic-based predictive models (or data mining models), RS and game theory techniques can provide accurate maps of dust source areas in arid and semi-arid regions, which can be helpful for mitigation of negative effects of dust storms.

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Using statistical models and GIS to delimit the groundwater recharge potential areas and to estimate the infiltration rate: A case study of Nadhour-Sisseb-El Alem Basin, Tunisia
Ali SOUEI, Taher ZOUAGHI
Journal of Arid Land    2021, 13 (11): 1122-1141.   DOI: 10.1007/s40333-021-0092-3
Abstract35)   HTML10)    PDF (2645KB)(242)      

The water resources of the Nadhour-Sisseb-El Alem Basin in Tunisia exhibit semi-arid and arid climatic conditions. This induces an excessive pumping of groundwater, which creates drops in water level ranging about 1-2 m/a. Indeed, these unfavorable conditions require interventions to rationalize integrated management in decision making. The aim of this study is to determine a water recharge index (WRI), delineate the potential groundwater recharge area and estimate the potential groundwater recharge rate based on the integration of statistical models resulted from remote sensing imagery, GIS digital data (e.g., lithology, soil, runoff), measured artificial recharge data, fuzzy set theory and multi-criteria decision making (MCDM) using the analytical hierarchy process (AHP). Eight factors affecting potential groundwater recharge were determined, namely lithology, soil, slope, topography, land cover/use, runoff, drainage and lineaments. The WRI is between 1.2 and 3.1, which is classified into five classes as poor, weak, moderate, good and very good sites of potential groundwater recharge area. The very good and good classes occupied respectively 27% and 44% of the study area. The potential groundwater recharge rate was 43% of total precipitation. According to the results of the study, river beds are favorable sites for groundwater recharge.

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A bibliometric analysis of carbon exchange in global drylands
LIU Zhaogang, CHEN Zhi, YU Guirui, ZHANG Tianyou, YANG Meng
Journal of Arid Land    2021, 13 (11): 1089-1102.   DOI: 10.1007/s40333-021-0112-3
Abstract35)   HTML20)    PDF (1122KB)(171)      

Drylands refer to regions with an aridity index lower than 0.65, and billions of people depend on services provided by the critically important ecosystems in these areas. How ecosystem carbon exchange in global drylands (CED) occurs and how climate change affects CED are critical to the global carbon cycle. Here, we performed a comprehensive bibliometric study on the fields of annual publications, marked journals, marked institutions, marked countries, popular keywords, and their temporal evolution to understand the temporal trends of CED research over the past 30 a (1991-2020). We found that the annual scientific publications on CED research increased significantly at an average growth rate of 7.93%. Agricultural Water Management ranked first among all journals and had the most citations. The ten most productive institutions were centered on drylands in America, China, and Australia that had the largest number and most citations of publications on CED research. "Climate change" and climate-related (such as "drought", "precipitation", "temperature", and "rainfall") research were found to be the most popular study areas. Keywords were classified into five clusters, indicating the five main research focuses on CED studies: hydrological cycle, effects of climate change, carbon and water balance, productivity, and carbon-nitrogen-phosphorous coupling cycles. The temporal evolution of keywords further showed that the areas of focus on CED studies were transformed from classical pedology and agricultural research to applied ecology and then to global change ecological research over the past 30 a. In future CED studies, basic themes (such as "water", "yield", and "salinity") and motor themes (such as "climate change", "sustainability", and "remote sensing") will be the focus of research on CED. In particular, multiple integrated methods to understand climate change and ecosystem sustainability are potential new research trends and hotspots.

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Variation of soil physical-chemical characteristics in salt-affected soil in the Qarhan Salt Lake, Qaidam Basin
HUI Rong, TAN Huijuan, LI Xinrong, WANG bingyao
Journal of Arid Land    2022, 14 (3): 341-355.   DOI: 10.1007/s40333-022-0091-z
Abstract35)   HTML6)    PDF (645KB)(65)      

Soil salinization has adverse effects on the soil physical-chemical characteristics. However, little is known about the changes in soil salt ion concentrations and other soil physical-chemical characteristics within the Qarhan Salt Lake and at different soil depths in the surrounding areas. Here, we selected five sampling sites (S1, S2, S3, S4, and S5) alongside the Qarhan Salt Lake and in the Xidatan segment of the Kunlun Mountains to investigate the relationship among soil salt ion concentrations, soil physical-chemical characteristics, and environmental variables in April 2019. The results indicated that most sites had strongly saline and very strongly saline conditions. The main salt ions present in the soil were Na+, K+, and Cl-. Soil nutrients and soil microbial biomass (SMB) were significantly affected by the salinity (P<0.05). Moreover, soil salt ions (Na+, K+, Ca2+, Mg2+, Cl-, CO32-, SO42-, and HCO3-) were positively correlated with electrical conductivity (EC) and soil water content (SWC), but negatively related to altitude and soil depth. Unlike soil salt ions, soil nutrients and SMB were positively correlated with altitude, but negatively related to EC and SWC. Moreover, soil nutrients and SMB were negatively correlated with soil salt ions. In conclusion, soil nutrients and SMB were mainly influenced by salinity, and were related to altitude, soil depth, and SWC in the areas from the Qarhan Salt Lake to the Xidatan segment. These results imply that the soil quality (mainly evaluated by soil physical-chemical characteristics) is mainly influenced by soil salt ions in the areas surrounding the Qarhan Salt Lake. Our results provide an accurate prediction of how the soil salt ions, soil nutrients, and SMB respond to the changes along a salt gradient. The underlying mechanisms controlling the soil salt ion distribution, soil nutrients, and SMB in an extremely arid desert climate playa should be studied in greater detail in the future.

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Modelling the biological invasion of Prosopis juliflora using geostatistical-based bioclimatic variables under climate change in arid zones of southwestern Iran
Mohadeseh AMIRI, Mosfata TARKESH, Mohammad SHAFIEZADEH
Journal of Arid Land    2022, 14 (2): 203-224.   DOI: 10.1007/s40333-022-0004-1
Abstract35)   HTML2)    PDF (1580KB)(65)      

Invasive species have been the focus of ecologists due to their undesired impacts on the environment. The extent and rapid increase in invasive plant species is recognized as a natural cause of global-biodiversity loss and degrading ecosystem services. Biological invasions can affect ecosystems across a wide spectrum of bioclimatic conditions. Understanding the impact of climate change on species invasion is crucial for sustainable biodiversity conservation. In this study, the possibility of mapping the distribution of invasive Prosopis juliflora (Swartz) DC. was shown using present background data in Khuzestan Province, Iran. After removing the spatial bias of background data by creating weighted sampling bias grids for the occurrence dataset, we applied six modelling algorithms (generalized additive model (GAM), classification tree analysis (CTA), random forest (RF), multivariate adaptive regression splines (MARS), maximum entropy (MaxEnt) and ensemble model) to predict invasion distribution of the species under current and future climate conditions for both optimistic (RCP2.6) and pessimistic (RCP8.5) scenarios for the years 2050 and 2070, respectively. Predictor variables including weighted mean of CHELSA (climatologies at high resolution for the Earth's land surface areas)-bioclimatic variables and geostatistical-based bioclimatic variables (1979-2020), physiographic variables extracted from shuttle radar topography mission (SRTM) and some human factors were used in modelling process. To avoid causing a biased selection of predictors or model coefficients, we resolved the spatial autocorrelation of presence points and multi-collinearity of the predictors. As in a conventional receiver operating characteristic (ROC), the area under curve (AUC) is calculated using presence and absence observations to measure the probability and the two error components are weighted equally. All models were evaluated using partial ROC at different thresholds and other statistical indices derived from confusion matrix. Sensitivity analysis showed that mean diurnal range (Bio2) and annual precipitation (Bio12) explained more than 50%of the changes in the invasion distribution and played a pivotal role in mapping habitat suitability of P. juliflora. At all thresholds, the ensemble model showed a significant difference in comparison with single model. However, MaxEnt and RF outperformed the others models. Under climate change scenarios, it is predicted that suitable areas for this invasive species will increase in Khuzestan Province, and increasing climatically suitable areas for the species in future will facilitate its future distribution. These findings can support the conservation planning and management efforts in ecological engineering and be used in formulating preventive measures.

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Assessment of river basin habitat quality and its relationship with disturbance factors: A case study of the Tarim River Basin in Northwest China
HE Bing, CHANG Jianxia, GUO Aijun, WANG Yimin, WANG Yan, LI Zhehao
Journal of Arid Land    2022, 14 (2): 167-185.   DOI: 10.1007/s40333-022-0058-0
Abstract34)   HTML4)    PDF (2012KB)(55)      

The status of regional biodiversity is determined by habitat quality. The effective assessment of habitat quality can help balance the relationship between economic development and biodiversity conservation. Therefore, this study used the InVEST model to conduct a dynamic evaluation of the spatial and temporal changes in habitat quality of the Tarim River Basin in southern Xinjiang Uygur Autonomous Region of China by calculating the degradation degree levels for habitat types that were caused by threat factors from 1990 to 2018 (represented by four periods of 1990, 2000, 2010 and 2018). Specifically, we used spatial autocorrelation analysis and Getis-Ord G* i analysis to divide the study area into three heterogeneous units in terms of habitat quality: cold spot areas, hot spot areas and random areas. Hemeroby index, population density, gross domestic product (GDP), altitude and distance from water source (DWS) were then chosen as the main disturbance factors. Linear correlation and spatial regression models were subsequently used to analyze the influences of disturbance factors on habitat quality. The results demonstrated that the overall level of habitat quality in the TRB was poor, showing a continuous degradation state. The intensity of the negative correlation between habitat quality and Hemeroby index was proven to be strongest in cold spot areas, hot spot areas and random areas. The spatial lag model (SLM) was better suited to spatial regression analysis due to the spatial dependence of habitat quality and disturbance factors in heterogeneous units. By analyzing the model, Hemeroby index was found to have the greatest impact on habitat quality in the studied four periods (1990, 2000, 2010 and 2018). The research results have potential guiding significance for the formulation of reasonable management policies in the TRB as well as other river basins in arid areas.

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Contribution of underlying terrain to sand dunes: evidence from the Qaidam Basin, Northwest China
LI Jiyan, QU Xin, DONG Zhibao, CAI Yingying, LIU Min, REN Xiaozong, CUI Xujia
Journal of Arid Land    2021, 13 (12): 1215-1229.   DOI: 10.1007/s40333-021-0028-y
Abstract34)   HTML16)    PDF (3434KB)(224)      

Underlying terrain strongly influences dune formation. However, the impacts of underlying terrain on the dune formation are poorly studied. In the present research, we focused on dunes that formed in the alluvial fans and dry salt flats in the Qaidam Basin, Northwest China. We quantified the dunes' sediment characteristics on different types of underlying terrain and the terrain's effects on the surface quartz grains by analyzing grain-size distribution, soluble salt contents and grain surface micro-textures. Results showed that barchan dunes were dominated by medium sands with a unimodal frequency distribution, whose peak corresponded to the saltation load. Linear dunes were mainly composed of fine sands with a bimodal frequency distribution, whose main peak represented the saltation load, and whose secondary peak represented the modified saltation or suspension load. Sand was transported from source area by running water (inland rivers) over short distances and by wind over relatively longer distances. Thus, quartz grains had poor roundness and were dominated by sub-angular and angular shapes. Surface micro-textures indicated that dune sands were successively transported by exogenic agents (glaciation, fluviation and wind). Soluble salt contents were low in dunes that developed in the alluvial fans, which represented a low-energy chemical environment, so the grain surface micro-textures mainly resulted from mechanical erosion, with weak micro-textures formed by SiO2 solution and precipitation. However, soluble salt contents were much higher in dunes that developed in the dry salt flats, which indicated a high-energy chemical environment. Therefore, in addition to micro-structures caused by mechanical erosion, micro-textures formed by SiO2 solution and precipitation also well developed. Our results improve understanding of the sediment characteristics of dune sands and the effects of underlying terrain on dune development in the Qaidam Basin, China.

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Scenario simulation of water retention services under land use/cover and climate changes: a case study of the Loess Plateau, China
SUN Dingzhao, LIANG Youjia, PENG Shouzhang
Journal of Arid Land    2022, 14 (4): 390-410.   DOI: 10.1007/s40333-022-0054-4
Abstract32)   HTML6)    PDF (3611KB)(32)      

Comprehensive assessments of ecosystem services in environments under the influences of human activities and climate change are critical for sustainable regional ecosystem management. Therefore, integrated interdisciplinary modelling has become a major focus of ecosystem service assessment. In this study, we established a model that integrates land use/cover change (LUCC), climate change, and water retention services to evaluate the spatial and temporal variations of water retention services in the Loess Plateau of China in the historical period (2000-2015) and in the future (2020-2050). An improved Markov-Cellular Automata (Markov-CA) model was used to simulate land use/land cover patterns, and ArcGIS 10.2 software was used to simulate and assess water retention services from 2000 to 2050 under six combined scenarios, including three land use/land cover scenarios (historical scenario (HS), ecological protection scenario (EPS), and urban expansion scenario (UES)) and two climate change scenarios (RCP4.5 and RCP8.5, where RCP is the representative concentration pathway). LUCCs in the historical period (2000-2015) and in the future (2020-2050) are dominated by transformations among agricultural land, urban land and grassland. Urban land under UES increased significantly by 0.63×103 km2/a, which was higher than the increase of urban land under HS and EPS. In the Loess Plateau, water yield decreased by 17.20×106 mm and water retention increased by 0.09×106 mm in the historical period (2000-2015), especially in the Interior drainage zone and its surrounding areas. In the future (2020-2050), the pixel means of water yield is higher under RCP4.5 scenario (96.63 mm) than under RCP8.5 scenario (95.46 mm), and the pixel means of water retention is higher under RCP4.5 scenario (1.95 mm) than under RCP8.5 scenario (1.38 mm). RCP4.5-EPS shows the highest total water retention capacity on the plateau scale among the six combined scenarios, with the value of 1.27×106 mm. Ecological restoration projects in the Loess Plateau have enhanced soil and water retention. However, more attention needs to be paid not only to the simultaneous increase in water retention services and evapotranspiration but also to the type and layout of restored vegetation. Furthermore, urbanization needs to be controlled to prevent uncontrollable LUCCs and climate change. Our findings provide reference data for the regional water and land resources management and the sustainable development of socio-ecological systems in the Loess Plateau under LUCC and climate change scenarios.

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Impact of rainfed and irrigated agriculture systems on soil carbon stock under different climate scenarios in the semi-arid region of Brazil
André L CARVALHO, Renato A ARAÚJO-NETO, Guilherme B LYRA, Carlos E P CERRI, Stoécio M F MAIA
Journal of Arid Land    2022, 14 (4): 359-373.   DOI: 10.1007/s40333-022-0092-y
Abstract31)   HTML9)    PDF (916KB)(110)      

Understanding the dynamics of soil organic carbon (SOC) is of fundamental importance in land use and management, whether in the current researches or in future scenarios of agriculture systems considering climate change. In order to evaluate SOC stock of the three districts (Delmiro Gouveia, Pariconha, and Inhapi districts) in the semi-arid region of Brazil in rainfed and irrigated agriculture systems under different climate scenarios using the Century model, we obtained RCP4.5 and RCP8.5 climate scenarios derived from the Eta Regional Climate Model (Eta-HadGEM2-ES and Eta-MIROC5) from the National Institute for Space Research, and then input the data of bulk density, pH, soil texture, maximum temperature, minimum temperature, and rainfall into the soil and climate files of the Century model. The results of this study showed that the Eta-HadGEM2-ES model was effective in estimating air temperature in the future period. In rainfed agriculture system, SOC stock under the baseline scenario was lower than that under RCP4.5 and RCP8.5 climate scenarios, while in irrigated agriculture system, SOC stock in the almost all climate scenarios (RCP4.5 and RCP8.5) and models (Eta-HadGEM2-ES and Eta-MIROC5) will increase by 2100. The results of this study will help producers in the semi-arid region of Brazil adopt specific agriculture systems aimed at mitigating greenhouse gas emissions.

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Delayed seed dispersal species and related traits in the desert of the United Arab Emirates
Teresa NAVARRO, Hatem A SHABANA, Ali EL-KEBLAWY, Noelia HIDALGO-TRIANA
Journal of Arid Land    2021, 13 (9): 962-976.   DOI: 10.1007/s40333-021-0018-0
Abstract31)   HTML7)    PDF (397KB)(285)      

The ability of plants to safely retain seeds in the mother plant is an adaptive mechanism described in many desert plants. However, research about delayed seed dispersal species in the desert of the United Arab Emirates (UAE) is lacking. This study aims to identify these delayed seed dispersal species and assess the relationships of the presence of delayed seed dispersal with plant growth form, habit, spatial dispersal, antitelechoric mechanism, and seed release time. The relationships between the presence of delayed seed dispersal and the above studied traits were assessed by using the Pearson Chi-square test and Nonlinear Principal Components Analysis (NLPCA). Results showed that a total of 46 delayed seed dispersal species were recorded (15.0% of 307 studied species) and the highest incidence occurred in the Fabaceae family (17.4%). Delayed seed dispersal species were predominantly perennial plants (73.9%) with spatial restricted dispersal (67.4%), which released seed in the dry season (45.7%). The dominant groups of delayed seed dispersal species were persistent fruits species and synaptospermy (28.3%). All graminoids showed persistent lignified fruits, while prostrate annuals were basicarpic species with myxospermy. Sandy habitats had the highest number of delayed seed dispersal species (54.3%), whereas salt flats had the lowest (23.9%). In the desert of the UAE, delayed seed dispersal species spread seeds until the end of the dry and windy season, thus breaking seed dormancy at this time and ensuring seed germination in the next arrival of the rainy season. This morphological and ecological adaptation of delayed dispersal species is essential to the survival and sustainable development of vegetation in desert environments.

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