Abstract
Flash droughts are a recently recognized extreme climate phenomena that
occur at the subseasonal timescale and develop with sudden onset and
rapid intensity, which have significant socio-environmental impacts on
agriculture, ecosystem, and water resources. However, the spatial and
temporal variability of flash droughts in the continental United States
(CONUS) are still not well understood. In this study, we characterize
flash drought events using a novel evaporative demand flash drought
(EDFD) index as well as a soil moisture flash drought (SMFD) index at
the weekly timescale between September 1981 and December 2018.
Hierarchical clustering divided CONUS into different clusters where
SMFDs occur synchronously over space and time. The results show that
flash droughts occur in all seasons and regions in CONUS with increasing
trends in EDFDs (0.07 > tau > 0.28), but not
equal trends in SMFDs (-0.12 > tau > 0.08).
Periodic short-term behavior between EDFDs and SMPDs was identified in
all clusters but more importantly long-term oscillatory behavior is
identified between the two indexes in all clusters except the Northwest
US. Our research into the spatiotemporal variability of flash droughts
using both the EDFD index and SMPD index displays that CONUS is still at
risk for increased flash drought events in the future to come.