Construction and application of a comprehensive drought index based on Copula function on a kilometer scale: A case study of Chongqing, China
YANG Chenfei1(), WU Tianjun2(), WANG Changpeng1, YANG Lijuan1, LUO Jiancheng3,4, ZHANG Xin3,4
1. School of Sciences, Chang’an University, Xi’an 710064, China 2. School of Land Engineering, Chang’an University, Xi’an 710064, China 3. State Key Laboratory of Remote Sensing Science, Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing 100101, China 4. College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, China
Drought is identified as one type of the most serious natural disasters affecting agricultural production, and developing a comprehensive drought index holds practical significance for the assessment of drought in various districts and counties in Chongqing. By coupling the soil moisture and precipitation Z-index data downscaled using the XGBoost algorithm and using the Copula function, this study developed a gridded comprehensive drought index CSDIM-A on a kilometer scale with the boundaries of various districts and counties of Chongqing as the spatial division criteria and decades of a month as time units. Using this index, this study assessed the spatiotemporal characteristics of drought and performed an experimental demonstration of the index using Chongqing as the study area. The results indicate that the downscaling enhanced the spatial continuity of remote sensing-based products, thus providing support for the subsequent construction of a comprehensive drought index on a kilometer scale. The generalized extreme value distribution and the t location-scale distribution applied to the fitting of the data distributions of soil moisture and precipitation in most districts and counties of Chongqing, respectively, while the Frank-copula function suited for the fitting of the joint distribution of binary variables on a scale of a month decade. As validated based on soil moisture content, CSDIM-A can more effectively reflect drought than the precipitation Z-index, with its spatial distribution in various districts and counties consistent with the actual drought data. This indicates that the CSDIM-A can be used as a reference for drought assessment.
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