The future intensification of hydrological extremes and whiplashes in the contiguous United States increase community vulnerability

Abstract

Hydroclimatic whiplash rapid shifts between drought and flood poses growing risks to U.S. communities. Here, we assess historical extremes and future projections using a normalized streamflow metric: the annual mean flow’s deviation from the 1981–2020 average, expressed as a fraction of that average. This metric is applied to United States Geological Survey records and Localized Constructed Analogs downscaled projections under Representative Concentration Pathways 4.5 and 8.5. Results reveal sharp regional disparities, with drought deficits exceeding 300% of normal flow during multi-year droughts. By linking hydrologic outcomes with the Federal Emergency Management Agency’s National Risk Index, we find that counties facing the deepest droughts also experience the highest annual losses and lowest resilience. Under the high-emissions scenario, sustained surpluses emerge only in already resilient regions. These findings highlight the urgent need for region-specific, adaptive water management to protect vulnerable populations from worsening climate extremes.