Characteristics and Causes of Meteorological Drought in Zhejiang Province (1971–2020): Insights from Comprehensive Discrimination Indices

This study examines the multi-scale spatio-temporal evolution of drought characteristics in Zhejiang Province. We propose a comprehensive index to identify drought days and events by incorporating three widely used monitoring indices: the precipitation anomaly percentage, relative humidity index, and standardized precipitation index. The analysis reveals a significant long-term decreasing trend in the frequency of drought days across Zhejiang Province from 1971 to 2020, with a total of 170 drought events being identified. An Empirical Orthogonal Function (EOF) analysis of precipitation anomalies during these events reveals a dominant province-wide monopole mode, alongside a secondary north-south inverse dipole, a third tripole, and a fourth southwest-northeast inverse dipole. Furthermore, a composite analysis of the drought events demonstrates a widespread increase in temperature across all stations, with a strong spatial correspondence between the temperature anomalies and their associated frequency. The study identifies 21 extreme drought events, characterized by spatially inconsistent precipitation patterns across the entire province.