Dynamic Evolution and Copula-Based Multivariable Frequency Analysis of Meteorological Drought Considering the Spatiotemporal Variability in Northwestern China

Meteorological drought is a continuous spatiotemporal phenomenon that poses a serious threat to water resource security. Dynamic evolution and multivariable frequency analysis of meteorological drought are important for effective drought mitigation and risk management. Therefore, this study aims to analyze meteorological drought events in northwestern China between 1960 and 2018 based on the standardized precipitation evapotranspiration index (SPEI) through a three-dimensional identification method. This study investigates the meteorological drought dynamic evolution on different time and space scales and evaluates the frequency analysis considering the spatiotemporal variability based on Copula. The results show that SPEI presents an upward trend in Northwestern China. A trend towards increased humidity is observed in arid regions, contrasted by a trend towards aridification in semi-arid and semi-humid areas, indicating that the spatial distribution of drought in the study area tends towards homogenization. The possibility of high-intensity drought events occurring in the same area was relatively low, whereas low-intensity drought events were frequent. Additionally, this study analyzes the dynamic migration process of individual drought events from a three-dimensional perspective. Neglecting any one drought variable could significantly underestimate the occurring probability of severe drought events. Therefore, a multivariable frequency analysis considering the spatiotemporal variability plays a crucial role in the formulation of drought prevention and mitigation strategies, as well as drought forecasting.