The spatiotemporal characteristics of extreme drought events in China from 1961 to 2022 via a copula function

In this study, a comprehensive and systematic analysis of extreme drought events in China from 1961 to 2022 utilizing the standardized precipitation index (SPI) and copula functions based on monthly gridded precipitation data is presented. In this study, drought events and their characteristics are identified using run theory and the 3-month SPI. A drought event with a joint exceedance probability of drought severity and duration calculated by the copula function at less than 5% was subsequently defined as an extreme drought. Under extreme drought conditions, the duration/severity of drought was fixed at a specific value, the corresponding drought severity/duration was calculated grid by grid, and its spatial heterogeneity and change were analyzed during two time periods (1961–1991 and 1992–2022). The results revealed significant temporal and spatial variations in drought trends, with increased precipitation severity in Northwest China and the Qinghai‒Tibet Plateau and more severe drought conditions in Northeast China and South China. The western part of Northwest China (Subregion 1) and the northern Qinghai–Tibet Plateau (Subregion 6) experienced longer and more severe drought events, characterized by average durations of 3.93 months and maximum severities up to 10.52 in Subregion 1, significantly exceeding national averages (3.47 months and 9.26). The duration/severity of extreme drought varied in different regions, with higher durations/severities in drought-prone areas. The frequency, duration, and severity of extreme drought events exhibited significant variations, particularly in central and southern China, where the frequency, duration, and severity of extreme drought events have increased. In subtropical humid regions in Central China and South China (Subregion 5), 47% of the grids experience an increase in the total number of occurrences, 54% of the grids experience an increase in the total number of months of occurrence, 64% of the grids experience an increase in the average severity, and 62% of the grids experience an increase in the maximum severity. Additionally, the number of extreme droughts caused by both duration and severity was greater than the number of extreme droughts dominated by any one factor alone. This study contributes to a more comprehensive assessment of extreme drought, providing a scientific basis for drought monitoring in China. • SPI & copula functions reveal spatiotemporal trends in extreme droughts, 1961-2022. • Copula-based thresholds show spatial heterogeneity in extreme drought conditions. • Observed drying trends in Northeast & South China with increasing extreme drought events. • Both duration and severity significantly contribute to extreme drought events across regions. • Comprehensive study provides insights into extreme drought characteristics, aiding monitoring efforts.