Propagation of meteorological to agricultural flash droughts using a novel weekly index

Anhui and Hubei province (108.3°E–119.5°E, 29°N–34.5°N) in China's Yangtze River basin. A novel weekly Flash Drought Index (FDI) based on soil moisture variables is introduced to address this challenge, offering a more effective approach for monitoring and assessing flash drought occurrences. The methodology involves defining severity thresholds for the FDI, validating its effectiveness, and monitoring the transition from meteorological to agricultural droughts. The results indicate that from 1961 to 2020, the frequency of flash droughts has steadily increased across all FDI monitoring timescales (FDI1 to FDI4), with the highest occurrences observed in July. Particularly severe conditions were found in Anhui Province, especially in its northwestern and southwestern regions, as well as in central and western Hubei. The average lag time for meteorological drought propagation to an agricultural flash drought ranged from 7.0 to 8.1 weeks, with northern Anhui showing significantly higher propagation rates, peaking at 43.6 % under FDI3. Hence, it is concluded that flash droughts are becoming both more frequent and more severe, with distinct regional patterns in their progression. • A new Flash Drought Index (FDI) based on soil moisture variables is developed for improved monitoring. • The study identifies distinct regional differences in flash drought propagation with accelerated transition rates. • Recommendations enhance early warning systems and implement region-specific drought management in northern Anhui.