Abstract
Flash droughts are characterized by a period of rapid intensification over sub-seasonal time scales that culminates in the rapid emergence of new or worsening drought impacts. This study presents a new flash drought intensity index (FDII) that accounts for both the unusually rapid rate of drought intensification and its resultant severity. The FDII framework advances our ability to characterize flash drought because it provides a more complete measure of flash drought intensity than existing classification methods that only consider the rate of intensification. The FDII is computed using two terms measuring the maximum rate of intensification (FD_INT) and average drought severity (DRO_SEV). A climatological analysis using soil moisture data from the Noah land surface model from 1979–2017 revealed large regional and interannual variability in the spatial extent and intensity of soil moisture flash drought across the US. Overall, DRO_SEV is slightly larger over the western and central US where droughts tend to last longer and FD_INT is ~75% larger across the eastern US where soil moisture variability is greater. Comparison of the FD_INT and DRO_SEV terms showed that they are strongly correlated (r = 0.82 to 0.90) at regional scales, which indicates that the subsequent drought severity is closely related to the magnitude of the rapid intensification preceding it. Analysis of the 2012 US flash drought showed that the FDII depiction of severe drought conditions aligned more closely with regions containing poor crop conditions and large yield losses than that captured by the intensification rate component (FD_INT) alone.
Highlights
Flash droughts are characterized by unusually rapid intensification over sub-seasonal time scales that culminates in drought conditions [1]
The similar seasonal distributions of flash drought occurrence across the central US when using soil moisture or evapotranspiration-based metrics could be due to stronger land–atmosphere coupling in this region [54,55,56,57,58]
This study presents a new flash drought monitoring framework that explicitly accounts for both the rapid rate of intensification and the resultant drought severity when assessing the intensity of flash drought
Summary
Flash droughts are characterized by unusually rapid intensification over sub-seasonal time scales that culminates in drought conditions [1]. The co-occurrence of below normal precipitation and elevated evaporative demand can lead to the rapid depletion of root zone soil moisture due to the dual impacts of increased evapotranspiration and diminished recharge of soil moisture [2,4]. This in turn can lead to a rapid increase in vegetation moisture stress and the emergence of flash drought conditions [5,6,7,8]. Flash drought is a compound extreme climate event characterized by a combination of drivers and hazards that contribute to societal and environmental risks [9]
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