The Potential Utility of Solar-Induced chlorophyll Fluorescence and Evapotranspiration for Detecting Flash Droughts Onset over the United States

Conventional droughts develop gradually, which typically leave stakeholders enough time to prepare for the adverse impact. However, in the case of flash drought, the rapid onset of drought creates a series of challenges for drought monitoring and catches the stakeholders off guard. This study focuses on detecting the rapid change of vegetation function and hydrometeorological variables and analyzing their potential utility as flash drought onset detector, including the Solar-Induced chlorophyll Fluorescence (SIF), and the gap-filled MODIS/Terra evapotranspiration (ET) (MOD16A2GF). We chose the Rapid Intensification Index (RCI) to detect the rapid changes of SIF and ET, and compare the results with the United States Drought Monitor (USDM ) maps, using the 2012 and 2017 flash droughts as case studies. To help understand and interpret the rapid intensification of droughts, the antecedent hydrometeorological conditions preceding the flash droughts are also analyzed. The results showed that the SIF-based RCI metric performs well as a flash drought onset indicator and can predict drought intensifications in both 2012 and 2017 with a lead time of 5 to 7 weeks relative to USDM . The ET-based RCI successfully detected the drought intensification in 2012 but failed to capture the drought intensification in 2017 due to the antecedent hydrometeorological conditions.