Spatio-temporal characteristics and driving factors of flash drought recovery: From the perspective of soil moisture and GPP changes

Flash drought recovery is significant to evaluate the impact of flash drought and the resilience of ecosystem. However, the definition of flash drought recovery stage and its mechanism remain unclear, with limited research in this area. This study proposes the definitions of flash drought recovery stage based on soil moisture change and gross primary productivity (GPP) change. The spatio-temporal characteristics, driving factors and differences between two identifications are investigated in Xiang River Basin (XRB) and Wei River Basin (WRB), two typical humid and semiarid basins in China. The main results are as follows: (1) XRB has a slightly longer recovery time and a higher recovery rate in terms of soil moisture-based definition, while GPP-based definition shows similar recovery times for both basins, with WRB having a higher recovery rate. (2) Based on soil moisture-based definition, the recovery time and recovery rates of different flash drought events in the same basin vary greatly, while most flash drought events in both basins recover within 2*8 days in terms of GPP-based definition. (3) Under both definitions, regions with relatively higher precipitation, lower average temperature and lower solar radiation tend to have higher recovery rates and shorter recovery time. Besides, grasslands tend to recover more quickly from flash drought than forests with GPP-based definition. (4) The recovery stage with soil moisture-based definition begins with the changes in associated meteorological variables, while the recovery stage with GPP-based definition begins 8 to 2*8 days after the changes of meteorological variables occur. This study proposes preliminary definitions for the recovery stage of flash drought and reveals the mechanism underlying the flash drought recovery, which are crucial for understanding the evolution of flash drought and reducing the risks resulting from it.