Multivariate evaluation of flash drought across the United States

Authors: OTKIN, J - University Of Wisconsin; ZHONG, Y - University Of Wisconsin; FORD, T - University Of Illinois; Anderson, Martha; HAIN, C - Nasa Marshall Space Flight Center; HOELL, A - National Oceanic & Atmospheric Administration (NOAA); SVOBODA, M - University Of Nebraska; WANG, H - National Oceanic & Atmospheric Administration (NOAA)

Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/5/2024
Publication Date: 11/1/2024
Citation: Otkin, J., Zhong, Y., Ford, T.W., Anderson, M.C., Hain, C., Hoell, A., Svoboda, M., Wang, H. 2024. Multivariate evaluation of flash drought across the United States. Water Resources Research. https://doi.org/10.1029/2024WR037333.
DOI: https://doi.org/10.1029/2024WR037333

Interpretive Summary: Flash droughts are a special class of drought events that develop quickly due to hot and dry conditions, compounding effects of lower-than-average rainfall. Given the potential impacts on crop production and the limited time available for mitigation action, it is important to able to identify this sub-class of drought and understand the major drivers, regionally. The flash drought intensity index (FDII) was developed to characterize flash droughts in terms of rapidity of onset and severity of resulting impacts on crop water availability. In this study, the FDII is used to create a climatological record of flash droughts in the United States from 2001-2021. To better capture the full range of drivers and impacts of drought, this analysis looks at multiple variables including precipitation, atmospheric dryness, soil moisture, and evapotranspiration (crop water use). If FDII is high for all variables, this is good evidence of a flash drought with significant potential to impact production. The study found that, from this multiple variable perspective, the strongest flash droughts have tended to occur in the central and southeastern U.S. In addition, the seasonality of flash drought was investigated, showing differences in timing of peak occurrence regionally. Together, these studies will promote efforts to improve understanding of flash drought processes and the more comprehensive monitoring of flash drought evolution, both of which will aid development of robust drought early warning systems.

Technical Abstract: uses the flash drought intensity index (FDII) to develop a multivariate flash drought climatology for the contiguous U.S. using data from 2001-2021. The FDII method uses the rate of intensification (FD_INT) and subsequent drought severity (DRO_SEV) to determine when a flash drought occurred and the strength of the event. Overall, the results showed that flash drought occurrence and severity varied with season and region and was sensitive to the drought monitoring dataset used to compute the FDII. Precipitation-based datasets identified more flash droughts across the western U.S. whereas soil moisture and evapotranspiration datasets preferentially identified flash droughts across the central and eastern U.S. When assessed over the entire U.S., the most flash droughts were identified when using a dataset representing evaporative demand. For the precipitation datasets, the flash drought severity (FDII) was closely related to how quickly large precipitation deficits developed (FD_INT) whereas for the soil moisture and evapotranspiration datasets it was more closely tied to the magnitude of the drought conditions (DRO_SEV) after the period of rapid intensification. A combined dataset synthesizing information from multiple indicators showed that the strongest flash droughts from a multivariate perspective are located in the central and southeastern U.S. A seasonal analysis revealed a distinct seasonal cycle in flash drought onset across the western and central U.S. Together, the results illustrate the need to use a multivariate framework to identify and characterize the severity of flash droughts.