Assessing Changes in Heat-Stress, Precipitation, and Drought Extremes in the Northeastern United States from 1979-2022

Abstract

The Northeastern United States is vulnerable to both concurrent humid heat and heavy rainfall, and concurrent humid heat and drought. Understanding how the individual climate variables change from decade to decade is necessary for identifying periods of increasing risk and changes in distributions. This study examines decadal shifts in spatial distributions and magnitude of daily maximum wet-bulb temperature (WBT; incorporating heat and humidity), precipitation, and drought, as measured by atmospheric water balance: precipitation minus potential evapotranspiration (P–PET)), across the northeastern United States (37–48°N, 82–66°W) from 1979 to 2022 using ERA5 ECMWF reanalysis and CRU TS4.08 datasets. We define extreme events relative to a 1979-2000 reference period, with heat-stress and extreme precipitation > 85^th percentile and P-PET < 20^th percentile. Additionally, we compare trends in extreme events from an urban Washington, D.C. area with a rural Middleburg, Virginia area to investigate regional heterogeneity. Our findings show that the WBT distribution shifted right from 1979-2022, with an increase in its 85^th percentile from .71 K from 2010 to 2020 and positive summer linear trend of 0.0204 K per year. Precipitation remained right-skewed with its 85th percentile varying slightly from 6.61 to 6.93 mm. P–PET showed substantial decadal variability, with driest 20^th percentile of −0.81 mm, compared with −0.53 mm during 2020–2022. Urban Washington, D.C., exhibited slightly greater increases than rural Middleburg in the frequency of extreme precipitation and WBT events, with urban-minus-rural trends of +0.37 and +0.17 days per decade, respectively. Overall, humid heat shows the clearest increase from 1979-2022, whereas precipitation and atmospheric water balance are more strongly influenced by decadal variability with urban and rural differences. These findings suggest that continued warming will increase the frequency of humid-heat extremes and, when combined with heavy precipitation or drought, elevate compound-event risk across the Northeast U.S.