Spatiotemporal evolution characteristics of drought in Yunnan Province based on meteorological-agricultural comprehensive drought index

Abstract

[Objective] This study aims to develop a drought index suitable for the actual conditions of Yunnan Province, [Objective]ly reveal drought variation patterns, and achieve effective drought monitoring. [Methods] The meteorological drought index(Standardized Precipitation-Evapotranspiration Index, SPEI) and the agricultural drought index(Standardized Soil Moisture Index, SSMI) were combined using the entropy weight method to develop a new comprehensive drought index. Various drought indices were evaluated and screened using method such as correlation analysis, root mean square error, and standard deviation to identify the most suitable drought index for Yunnan Province. Then, based on the most suitable drought index, [Methods]such as the run theory and Mann-Kendall trend test were used to thoroughly analyze the spatiotemporal variation characteristics of drought in Yunnan Province. [Results] The comprehensive drought index outperformed other drought indices in reflecting drought conditions, showing correlations of 64% and 60% with meteorological and agricultural drought indices, respectively. Additionally, it showed 94.11% consistency with statistical drought records. During the 2009—2010 winter-spring consecutive drought events, the drought evolution pattern captured by this method showed high consistency with actual drought process. In terms of time, the COI values at both monthly and seasonal scales across the province showed a fluctuating downward trend over the past 20 years, indicating increased drought frequency and severity. Seasonally, drought conditions were the most severe in spring, followed by winter, while summer and autumn showed relatively milder conditions. However, summer drought showed a persistent intensification trend at a rate of 0.034 per year. Spatially, the drought intensity and severity in Yunnan Province showed a concentric pattern, decreasing outward from the central Yunnan. Severe and extremely severe droughts were mainly concentrated in southwest and central Yunnan in spring and winter, while mild and moderate droughts occurred more frequently in summer and autumn. Trend analysis further showed a significant weakening trend(p<0.05) in drought severity during spring, autumn, and winter. Specifically, about 60% to 70% of areas in spring and autumn showed a significant decrease. In contrast, summer showed significant drought intensification. About 25.93% of areas showed a notable increasing trend(p<0.05), particularly in central and southern Yunnan. In winter, about 12.96% of the northern Yunnan exhibited a significant increase in drought severity. [Conclusion] The COI proves to be more suitable for Yunnan Province than other drought indices. Summer drought shows a distinct intensification trend, with central and southern Yunnan experiencing the most significant increases.

Keywords

comprehensive drought index / entropy weight method / run theory / spatiotemporal distribution characteristics / trend test / influencing factors