Agricultural drought is a type of natural disaster that seriously impacts food security. Because the relationships among short-term rainfall, soil moisture, and crop growth are complex, accurate identification of a drought situation is difficult. In this study, using a conceptual model based on the relationship between water deficit and crop yield reduction, we evaluated the drought process in a typical rainfed agricultural region, Hailar county in Inner Mongolia autonomous region, China. To quantify drought, we used the precipitation-based Standardized Precipitation Index (SPI), the soil moisture-based Crop Moisture Index (CMI), as well as the Normalized Difference Vegetation Index (NDVI). Correlation analysis was conducted to examine the relationships between dekad-scale drought indices during the growing season (May–September) and final yield, according to data collection from 2000 to 2010. The results show that crop yield has positive relationships with CMI from mid-June to mid-July and with the NDVI anomaly throughout July, but no correlation with SPI. Further analysis of the relationship between the two drought indices shows that the NDVI anomaly responds to CMI with a lag of 1 dekad, particularly in July. To examine the feasibility of employing these indices for monitoring the drought process at a dekad time scale, a detailed drought assessment was carried out for selected drought years. The results confirm that the soil moisture-based vegetation indices in the late vegetative to early reproductive growth stages can be used to detect agricultural drought in the study area. Therefore, the framework of the conceptual model developed for drought monitoring can be employed to support drought mitigation in the rainfed agricultural region of Northern China.

The hydrological processes of mountainous watersheds in inland river basins are complicated. It is absolutely significant to quantify mountainous runoff for social, economic and ecological purposes. This paper takes the mountainous watershed of the Heihe Mainstream River as a study area to simulate the hydrological processes of mountainous watersheds in inland river basins by using the soil and water assessment tool (SWAT) model. SWAT simulation results show that both the Nash–Sutcliffe efficiency and the determination coefficient values of the calibration period (January 1995 to December 2002) and validation period (January 2002 to December 2009) are higher than 0.90, and the percent bias is controlled within ±5%, indicating that the simulation results are satisfactory. According to the SWAT performance, we discussed the yearly and monthly variation trends of the mountainous runoff and the runoff components. The results show that from 1996 to 2009, an indistinctive rising trend was observed for the yearly mountainous runoff, which is mainly recharged by lateral flow, and followed by shallow groundwater runoff and surface runoff. The monthly variation demonstrates that the mountainous runoff decreases slightly from May to July, contrary to other months. The mountainous runoff is mainly recharged by shallow groundwater runoff in January, February, and from October to December, by surface runoff in March and April, and by lateral flow from May to September.

Recent studies on alkaline soils of arid areas suggest a possible contribution of abiotic exchange to soil CO₂ flux (F_c). However, both the overall contribution of abiotic CO₂ exchange and its drivers remain unknown. Here we analyzed the environmental variables suggested as possible drivers by previous studies and constructed a function of these variables to model the contribution of abiotic exchange to F_c in alkaline soils of arid areas. An automated flux system was employed to measure F_c in the Manas River Basin of Xinjiang Uygur autonomous region, China. Soil pH, soil temperature at 0–5 cm (T_s), soil volumetric water content at 0–5 cm (θ_s) and air temperature at 10 cm above the soil surface (T_as) were simultaneously analyzed. Results highlight reduced sensitivity of F_c to T_s and good prediction of Fc by the model F_c=R₁₀Q₁₀^{(T_as–10)/10+r7q7(pH–7)}+λT_as+µθ_s+e which represents F_c as a sum of biotic and abiotic components. This presents an approximate method to quantify the contribution of soil abiotic CO₂ exchange to F_c in alkaline soils of arid areas.

Calcareous soil contains organic and inorganic carbon (C) pools, which both contribute to CO₂ emission during closed-jar incubation. The mineralization of organic C and dissolution of inorganic C are both related to soil moisture, but the exact effect of water content on CO₂ emission from calcareous soil is unclear. The objective of this experiment was to determine the effect of soil water content (air-dried, 30%, 70%, and 100% water-holding capacity (WHC)), carbonate type (CaCO₃ or MgCO₃), and carbonate amount (0.0, 1.0%, and 2.0%) on CO₂ emission from calcareous soil during closed-jar incubation. Soil CO₂ emission increased significantly as the water content increased to 70% WHC, regardless of whether or not the soil was amended with carbonates. Soil CO₂ emission remained the same or increased slowly as the soil water content increased from 70% WHC to 100% WHC. When the water content was ≤30% WHC, soil CO₂ emission from soil amended with 1.0% inorganic C was greater than that from unamended soil. When the soil water content was 70% or 100% WHC, CO₂ emission from CaCO₃ amended soil was greater than that from the control. Furthermore, CO₂ emission from soil amended with 2.0% CaCO₃ was greater than that from soil amended with 1.0% CaCO₃. Soil CO₂ emission was higher in the MgCO₃ amended soil than from the unamended soil. Soil CO₂ emission decreased as the MgCO₃ content increased. Cumulative CO₂ emission was 3–6 times higher from MgCO₃ amended soil than from CaCO₃ amended soil. There was significant interaction effect between soil moisture and carbonates on CO₂ emission. Soil moisture plays an important role in CO₂ emission from calcareous soil because it affects both biotic and abiotic processes during the closed-jar incubation.

Field irrigation experiments were conducted in the Hetao Irrigation District of Inner Mongolia, China, to study the effects of irrigation regimes on salt leaching in the soil profile. The data were used to calibrate and validate the HYDRUS-1D model. The results demonstrated that the model can accurately simulate the water and salt dynamics in the soil profile. The HYDRUS-1D model was then used to simulate 15 distinct irrigation scenarios. The results of the simulation indicated that irrigation amount did not have a significant effect on soil water storage but that increases in irrigation amount could accelerate salt leaching. However, when the irrigation amount was larger than 20 cm, the acceleration was not obvious. Compared with irrigating only once, intermittent irrigation had a better effect on increasing soil water storage and salt leaching, but excessive irrigation times and intervals did not improve salt leaching. In addition, we found that the irrigation regime of 20 cm, irrigated twice at 1-d intervals, might significantly increase salt leaching in the plough layer and decrease the risks of deep seepage and groundwater contamination.

The Hexi Corridor, our study area, is located in Northwest China and is also the most developed area of oasis farming in arid regions of Northwestern China. However, the rapid development of metallurgy and chemical industries in this region poses a great threat to the accumulation of heavy metals in crops. The objectives of this study are (1) to determine the influence of heavy metals on plant growth; (2) to assess the translocation capability of heavy metals in soil-plant system; and (3) to investigate the interaction between heavy metals. Pot experiments were conducted on cole (Brassica campestris L.) grown in the arid oasis soils singly and jointly treated with cadmium (Cd) and lead (Pb). Nine treatments were applied into the pots. Under the same planting conditions, three scenarios of Cd, Pb and Cd–Pb were designed to compare the interaction between Cd and Pb. The results showed that the response of cole weights to Cd, Pb and Cd–Pb treatments was slight, while Cd and Pb uptakes in cole were more sensitive to the single effects of Cd and Pb concentration in soils from the lower treatment levels. Under the influence of the single Cd, Pb and joint Cd–Pb treatments, Cd concentrations were lower in the cole roots than in the shoots, while for Pb, the results were opposite. Comparison studies revealed that the interaction of Cd and Pb could weaken the cole’s ability to uptake, concentrate and translocate heavy metals in arid oasis soils.

Disturbance in wind regime and sand erosion deposition balance may lead to burial and eventual vanishing of a site. This study conducted 3D computational fluid dynamics (CFD) simulations to evaluate the effect of a proposed city design on the wind environment of the Crescent Spring, a downwind natural heritage site located in Dunhuang, Northwestern China. Satellite terrain data from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Digital Elevation Model (DEM) were used to construct the solid surface model. Steady-state Reynolds Averaged Navier-Stokes equations (RANS) with shear stress transport (SST) k-ω turbulence model were then applied to solve the flow field problems. Land-use changes were modeled implicitly by dividing the underlying surface into different areas and by applying corresponding aerodynamic roughness lengths. Simulations were performed by using cases with different city areas and building heights. Results show that the selected model could capture the surface roughness changes and could adjust wind profile over a large area. Wind profiles varied over the greenfield to the north and over the Gobi land to the east of the spring. Therefore, different wind speed reduction effects were observed from various city construction scenarios. The current city design would lead to about 2 m/s of wind speed reduction at the downwind city edge and about 1 m/s of wind speed reduction at the north of the spring at 35-m height. Reducing the city height in the north greenfield area could efficiently eliminate the negative effects of wind spee. By contrast, restricting the city area worked better in the eastern Gobi area compared with other parts of the study area. Wind speed reduction in areas near the spring could be limited to 0.1 m/s by combining these two abatement strategies. The CFD method could be applied to simulate the wind environment affected by other land-use changes over a large terrain.

As climate change negotiations progress, monitoring biomass and carbon stocks is becoming an important part of the current forest research. Therefore, national governments are interested in developing forest-monitoring strategies using geospatial technology. Among statistical methods for mapping biomass, there is a nonparametric approach called k-nearest neighbor (kNN). We compared four variations of distance metrics of the kNN for the spatially-explicit estimation of aboveground biomass in a portion of the Mexican north border of the intertropical zone. Satellite derived, climatic, and topographic predictor variables were combined with the Mexican National Forest Inventory (NFI) data to accomplish the purpose. Performance of distance metrics applied into the kNN algorithm was evaluated using a cross validation leave-one-out technique. The results indicate that the Most Similar Neighbor (MSN) approach maximizes the correlation between predictor and response variables (r=0.9). Our results are in agreement with those reported in the literature. These findings confirm the predictive potential of the MSN approach for mapping forest variables at pixel level under the policy of Reducing Emission from Deforestation and Forest Degradation (REDD+).

Disturbance can affect biomass allocation of plants, but can it influence plant reproductive behavior? To address this issue, we performed field plant community investigations and explored the reproductive behaviors of Stipa grandis and Stipa krylovii in response to grazing and mowing treatments at Maodeng pasture of Xilinguole League of Inner Mongolia, China during 2007–2009. The results showed that, with a similar niche width for the two plant species under mowing and grazing treatments, mowing significantly increased the ratio of ramet to genet number of S. krylovii and the carbon to nitrogen ratio of S. grandis, and grazing significantly decreased the ratio of vegetative to reproductive tiller biomass of S. grandis and increased the ratio of vegetative to reproductive tiller number of S. krylovii. Regression analysis showed that the significantly positive effect of root to shoot biomass ratio was stronger on the ratio of vegetative to reproductive tiller number of S. grandis than on that of S. krylovii. These results indicated that grazing and mowing influenced the reproductive manner and the process of sexual reproduction of S. grandis and S. krylovii.

Stemflow of xerophytic shrubs represents a significant component of water replenishment to the soil-root system and influences water utilization of plant roots at the stand scale, especially in water-scarce semi-arid ecosystems. The stemflow of two semi-arid shrubs (Caragana korshinskii and Hippophae rhamnoides) and its effect on soil moisture enhancement were evaluated during the growing season of 2011 in the semi-arid loess region of China. The results indicated that stemflow averaged 12.3% and 8.4% of the bulk precipitation for C. korshinskii and H. rhamnoides, respectively. Individual stemflow increased in a linear function with increasing rain-fall depth. The relationship between funneling ratios and rainfall suggested that there existed a rainfall depth threshold of 11 mm for both C. korshinskii and H. rhamnoides. Averaged funneling ratios were 156.6±57.1 and 49.5±30.8 for C. korshinskii and H. rhamnoides, respectively, indicating that the canopy architecture of the two shrubs was an effective funnel to channel stemflow to the root area, and C. korshinskii showed a greater potential to use stemflow water in the semi-arid conditions. For individual rainfall events, the wetting front depths were approximately 2 times deeper in the rooting zone around the stems than in the bare area outside canopy for both C. korshinskii and H. rhamnoides. Correspondingly, soil water content was also significantly higher in the root area around the shrub stem than in the area outside the shrub canopy. This confirms that shrub stemflow conserved in the deep soil layers may be an available moisture source for plant growth under semi-arid conditions.

Livestock ranching is one of the main productive activities in arid regions of the world. Grazing produces changes in animal as well as plant communities (e.g. richness, abundance and species dominance relationships). Ants are good biological indicators due to the environmental fidelity of some of their community parameters. We described the functional structure of the ant community in the central Monte of Mendoza, Argentina, and examined the effect of grazing using richness, diversity and the functional group scheme. We used pitfall traps to sample ants at a reserve with 30-year cattle exclusion and at an adjacent ranch. Eleven of the 27 recorded species showed significant differences in their abundance and two species were absent at the ranch. While richness and diversity did not reflect these differences, functional groups did. Hot Climate Specialists were more abundant at the ranch while Cryptic Species and Generalized Myrmicinae increased at the reserve. This study supports the utility of the functional group scheme to study the effects of grazing disturbance in ant communities of arid regions.