Lagged Soil Moisture Controls on the Persistence of Drought and Heatwaves in the United States

Abstract

Surface soil moisture (SSM) and root-zone soil moisture (RZSM) play critical roles in shaping heatwaves and droughts, yet their distinct controls remain unclear. Using 46 years of North American Land Data Assimilation System Phase 2 data and event coincidence analysis across the contiguous United States, we demonstrate that SSM primarily drives heatwaves in semiarid and sub-humid regions (median MaxTCR ≈ 0.63) through rapid surface drying, which shifts energy from latent to sensible heat. During droughts, RZSM has stronger influence in the central Great Plains (MaxTCR ≈ 0.64–0.71) with 3–5 months lags, indicating prolonged control over transpiration, compared with shorter lags (0–1 month; MaxTCR ≈ 0.44) in the Southwest. Analysis of three major events indicates that RZSM depletion intensified extremes in sub-humid and humid regions by suppressing transpiration and evaporative cooling, whereas sparse vegetation limited these feedbacks in arid regions. Incorporating lagged RZSM data can improve early warning systems for extreme events.