Unravelling spatiotemporal propagation processes among meteorological, soil, and evaporative flash droughts from a three-dimensional perspective

Flash droughts, defined by their rapid development and intensification, have received growing attention due to their severe impacts. Understanding the mechanisms and evolutions of flash drought events is crucial for early warning and mitigation. However, research on the propagation processes among different flash drought types remains limited. Here we developed a spatiotemporal matching framework to identify propagation processes among meteorological, soil, and evaporative flash droughts from a three-dimensional perspective, applying it to the middle and lower reaches of Yangtze River Basin (MLRYRB) from 2000 to 2022. Additionally, we utilized the random forest model to identify critical factors influencing flash drought propagation. Results showed that among three flash drought types, evaporative flash droughts exhibited the lowest number, duration, and severity, while soil flash droughts displayed the highest. The spatiotemporal matching framework identified 21 meteorological-soil, 12 meteorological-evaporative, 10 soil-evaporative, 19 evaporative-soil, 8 meteorological-soil-evaporative, and 4 meteorological-evaporative-soil flash drought propagation events in the MLRYRB, whereas minor flash droughts with short durations and limited areas failed to pair. Propagation towards evaporative flash droughts was associated with reduced duration, areas, and severity, while intensifying characteristics of flash droughts were observed in the propagation towards soil flash droughts. Vapor pressure deficit (VPD) and temperature were the main factors influencing propagations toward soil and evaporative flash droughts, respectively. Our findings can provide valuable insights into flash drought propagation processes and mechanisms, aiding in the establishment of flash drought early warning system and supporting policymakers in formulating adaptive agricultural water supply polices. • A spatiotemporal framework was developed to identify the flash drought propagation. • Differences in spatiotemporal features of three flash drought types were analyzed. • Propagation characteristics were examined from a three-dimensional perspective. • VPD and temperature played critical roles in influencing flash drought propagation.