Human-induced intensification of flash drought risk in the Anthropocene

Droughts were climate anomalies that occurred naturally, affected a large area and persist for a long time. However, climate change and human interventions have altered the characteristics of droughts, resulted in a new type of drought that has a rapid onset and severe impacts without sufficient early warning. This is termed as “flash drought” that occurred frequently worldwide in recent years. There has been progresses regarding flash drought definition, impact identification and analysis of spatiotemporal variations, but whether human interventions play an important role in altering the long-term changes of flash droughts or increasing the risk of the occurrence of a specific flash drought event remains unknown. Here, we propose a new method for explicitly characterizing flash drought events based on soil moisture deficit, and attribute historical trends and project future changes of flash drought risk by conducting climate-hydrology multimodel ensemble simulation over China, where natural and anthropogenic climate change scenarios provided by 11 CMIP5 models are used to drive 3 land surface hydrological models (CLM4.5, VIC, Noah-MP) for superensemble simulations. We find a significant increase in flash drought risk over China during the middle and end of this century. The increasing flash drought risk is mainly caused by greenhouse gas-induced anthropogenic climate change, where both long-term warming and increasing rainfall variability lead to a drier but more variable soil condition over the flash drought hotspots. With an urgent need to adapting to the increasing flash drought risk, the latest CMIP6 soil moisture data are being used to diagnose a severe flash drought event occurred over the lower reaches of the Yangtze River in Eastern China in the summer of 2019, and the contribution of human-induced climate change on the 2019 flash drought event is being assessed.