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Publication Date
28 July 2022

Changing Trends in Drought Patterns Over the Northeastern U.S. (NEUS)

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Normalized Regional Monthly Mean Precipitation and Evapotranspiration at the Spring

Droughts are extreme events with the potential to produce considerable social and economic damage.  Because droughts emerge slowly and are infrequent, large datasets are needed to study these features.  Using multiple climate models and a novel drought index, we characterize rapidly developing droughts and understand their drivers in the Northeastern US.  We find that short-term extreme droughts will be more frequent, while rapidly developing droughts will become more intense in the spring season.  Such intensification is attributed to differences in patterns of precipitation and evapotranspiration, which will be magnified by an extended growing season and an increase in vegetation.


By using large ensemble climate models and a novel drought index, we can quantify the drought pattern changes at multiple temporal scales between historical and future periods with far reduced uncertainty. Rapidly developing droughts (those flash droughts identifiable from monthly data) are then identified by the one-month SNPI, and subsequent analysis reveals that they are projected to increase significantly in the spring season. This study finds that their intensification is associated with an increase in evapotranspiration from plants, brought on by an earlier emergence of the growing season and denser vegetation. This study provides an answer to a previously unaddressed question – why will flash droughts intensify in the future?


To better explore the processes governing extreme events like the drought, climate models have adopted more complex representations of the fully coupled atmosphere-land-ocean-sea ice system; however, large uncertainties in future projections still persist, with internal variability necessitating large ensembles to understand trends in both rare and high-impact extreme events such as rapidly developing droughts (a term here that includes flash droughts developing on monthly scales). In this study, 7 large ensembles (LE) models are employed to answer the outstanding questionhow will the frequency and character of drought in the NEUS change under a warming climate? We find most LE models indicate the NEUS will experience a long-term wetting trend with more “extremely wet” months, but also more frequent short-term extreme droughts. These changes are associated with increasing precipitation, atmospheric water demand, and climate variability. We also conclude that discrepant trends in precipitation and evapotranspiration variability will lead to increasing anti-correlation of these variables, which is relevant to the intensification of rapidly developing droughtparticularly in the spring season. These changes are explained by an increase in evapotranspiration from plants, brought by an earlier emergence of the growing season and denser vegetation.

Point of Contact
Paul Ullrich
University of California Davis (UC Davis)
Funding Program Area(s)