Flash droughts characterization over China: From a perspective of the rapid intensification rate

Flash droughts, with rapid onset and strong intensity, have attracted much attention in recent literature due to their devastating socio-agricultural impacts. Based on the microwave remote sensing soil moisture data released by the European Space Agency Climate Change Initiative program (ESA CCI SM), flash droughts were identified by focusing on the attenuation rate of weekly soil moisture percentile. On this basis, the spatiotemporal patterns of flash drought frequency, their evolution process combined with meteorological conditions, and the relationship with seasonal droughts were analyzed. Results showed that the frequency of flash drought occurrence over China during 2000-2016 mainly varied between 6% and 20%. Spatially, such events were most likely to occur in the northern and southern region, and the Qinghai-Tibet Plateau showed the lowest frequency of occurrence. Influenced by the complex roles of negative anomalies of precipitation and relative humidity, along with positive anomalies of potential evapotranspiration (PET) and temperature, the southwest region suffered three severe drought attacks in summer 2006. In addition, a coexisting relationship was also observed between flash droughts and seasonal droughts. Initiated by the rapid reduction of soil moisture, the northern, northeastern, southern, and southwestern areas were more vulnerable to droughts with duration no more than 12 weeks. In contrast, the southern China were likely to suffer longer periods of droughts (more than 12 weeks) in spring (April to May), while for southwestern regions such type of droughts were mainly concentrated in summer (June and July).