Abstract
Understanding the characteristics of flash drought events and further predicting the onset of such events on subseasonal timescales is of critical importance for impact assessment, disaster mitigation, and loss prevention. In this study, we employ a rate-of-change approach and define a flash drought event as a drought event with greater than or equal to two categories degradation in a four-week period based on the U.S. Drought Monitor. Unlike conventional drought, which can occur year-round and everywhere in the United States, flash drought has preferred seasons and locations to occur, mostly in the warm season and over the central United States. Widespread flash drought over the United States is largely correlated with La Niña episodes. In contrast with conventional drought, which is mainly driven by precipitation deficits, anomalously high evapotranspiration rates, caused by anomalously high temperatures, winds, and/or incoming radiation, are usually present before the onset of flash drought. Comparing to precipitation and soil moisture, evapotranspiration typically has the largest decline rate during the fast-development phase. Three-month Standardized Precipitation Indexes are mostly dry right before flash drought onset, but large deficits are not required. As a result, monitoring rapid changes in evapotranspiration, along with precipitation and soil moisture conditions, can provide early warnings of flash drought development.
Highlights
Drought can develop and intensify in a short period of time and result in major agricultural losses if it is not predicted and detected in a timely manner
In order to improve our understanding of flash drought and better forecast its onset, we carry out a climatological analysis by examining fast-developing drought events identified from U.S Drought Monitor (USDM)
These results are consistent with the analysis of selected flash droughts and further support the onset, seven-day Standardized Evapotranspiration Index (SETI) were positive in most areas (Figure 9c), while there were a mix of positives findings from the previous section
Summary
Drought can develop and intensify in a short period of time and result in major agricultural losses if it is not predicted and detected in a timely manner. In order to improve our understanding of flash drought and better forecast its onset, we carry out a climatological analysis by examining fast-developing drought events identified from USDM. This approach is different from the approach used by Christian et al (2019) [9] or QuickDRI. USDM maps are produced weekly through expert synthesis of various data sources, including precipitation, soil moisture, streamflow, snow water equivalent and snowpack, crop and vegetation conditions, and reservoir and groundwater levels These data sources are coupled with inputs from local, state, regional, and federal levels (e.g., local impact reports) to depict short- and long-term drought conditions. The hourly NLDAS-2 outputs were aggregated to daily data from 00Z to 00Z for the analyses, and the rasterized USDM data were mapped to the NLDAS-2 grid system to be consistent
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