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Journal of Arid Land  2021, Vol. 13 Issue (12): 1244-1259    DOI: 10.1007/s40333-021-0111-4
Original article     
Drought and flood characteristics in the farming- pastoral ecotone of northern China based on the Standardized Precipitation Index
CAO Huicong1,2,*(), YAN Dandan3, JU Yuelin2
1Journal Department, Nanjing Forestry University, Nanjing 210037, China
2Faculty of Humanities & Social Sciences, Nanjing Forestry University, Nanjing 210037, China
3College of Biology and the Environment, Nanjing Forestry University, Nanjing 210037, China
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The farming-pastoral ecotone of northern China (FPENC) provides an important ecological barrier which restrains the invasion of desert into Northwest China. Studying drought and flood characteristics in the FPENC can provide scientific support and practical basis for the protection of the FPENC. Based on monthly precipitation data from 115 meteorological stations, we determined the changes in climate and the temporal and spatial variations of drought and flood occurrence in the FPENC during 1960-2020 using the Standardized Precipitation Index (SPI), Morlet wavelet transform, and inverse distance weighted interpolation method. Annual precipitation in the FPENC showed a slightly increasing trend from 1960 to 2020, with an increasing rate of about 1.15 mm/a. The interannual SPI exhibited obvious fluctuations, showing an overall non-significant upward trend (increasing rate of 0.02/a). Therefore, the study area showed a wetting trend in recent years. Drought and flood disasters mainly occurred on an interannual change cycle of 2-6 and 9-17 a, respectively. In the future, a tendency towards drought can be expected in the FPENC. The temporal and spatial distribution of drought and flood differed in the northwestern, northern, and northeastern segments of the FPENC, and most of the drought and flood disasters occurred in local areas. Severe and extreme drought disasters were concentrated in the northwestern and northeastern segments, and severe and extreme flood disasters were mainly in the northeastern segment. Drought was most frequent in the northwestern segment, the central part of the northeastern segment, and the northern part of the northern segment. Flood was most frequent in the western part of the northwestern segment, the eastern part of the northeastern segment, and the eastern and western parts of the northern segment. The accurate evaluation of the degrees of drought and flood disasters in the FPENC will provide scientific basis for the regional climate study and critical information on which to base decisions regarding environmental protection and socio-economic development in this region.

Key wordsfarming-pastoral ecotone of northern China (FPENC)      Standardized Precipitation Index (SPI)      drought      flood      Morlet wavelet transform     
Received: 18 August 2021      Published: 10 December 2021
Corresponding Authors: *CAO Huicong (E-mail:
Cite this article:

CAO Huicong, YAN Dandan, JU Yuelin. Drought and flood characteristics in the farming- pastoral ecotone of northern China based on the Standardized Precipitation Index. Journal of Arid Land, 2021, 13(12): 1244-1259.

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Fig. 1 Overview of the farming-pastoral ecotone of northern China (FPENC). The dotted line divides the FPENC into three parts: northwestern segment, northern segment, and northeastern segment.
Drought/flood grade SPI
Extreme flood SPI≥2.0
Severe flood 1.5≤SPI<2.0
Moderate flood 1.0≤SPI<1.5
Light flood 0.5≤SPI<1.0
Normal -0.5<SPI<0.5
Light drought -1.0<SPI≤ -0.5
Moderate drought -1.5<SPI≤ -1.0
Severe drought -2.0<SPI≤ -1.5
Extreme drought SPI≤ -2.0
Table 1 Classification standard of drought and flood grades based on the Standardized Precipitation Index (SPI)
Fig. 2 Annual precipitation change in the farming-pastoral ecotone of northern China (FPENC) from 1960 to 2020
Fig. 3 Standardized Precipitation Index (SPI) values with time-scales of 3-months (SPI-3; a) and 12-months (SPI-12; b) in the FPENC from 1960 to 2020
Fig. 4 Isolines of the real part of the Morlet wavelet coefficients (a) and the wavelet variance for the SPI-12 (b) in the FPENC from 1960 to 2020
Fig. 5 Change of the drought (or flood) station rate in the FPENC from 1960 to 2020
Period No obvious drought Drought in local areas Drought in partial areas Regional drought Drought event of the whole region
1960-1969 1 5 3 1 0
1970-1979 1 5 3 0 1
1980-1989 1 4 3 2 0
1990-1999 1 4 3 2 0
2000-2009 0 2 3 5 0
2010-2020 1 8 2 0 0
Period No obvious flood Flood in local areas Flood in partial areas Regional
Flood event of the whole region
1960-1969 1 4 2 2 1
1970-1979 1 4 4 1 0
1980-1989 2 4 3 1 0
1990-1999 2 1 5 2 0
2000-2009 2 7 1 0 0
2010-2020 0 3 3 5 0
Table 2 Statistics of drought and flood at different spatial scales in the farming-pastoral ecotone of northern China (FPENC) from 1960 to 2020
Fig. 6 Spatial distribution characteristics of drought and flood grades in the FPENC in 1960 (a), 1970 (b), 1980 (c), 1990 (d), 2000 (e), 2010 (f), and 2020 (g)
Fig. 7 Spatial distribution of drought (a-e) and flood (f-j) frequency in the FPENC
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