Wetlands set the pace of annual runoff in the northern Great Plains

Abstract Interannual variability in the runoff ratio—how much annual precipitation becomes streamflow—underpins water management, flood forecasting, and biogeochemical fluxes. In most hydrologic frameworks, this variability is attributed primarily to year-to-year climate drivers. Here, we show that in North America’s wetland-rich Prairie Pothole Region, wetlands play the dominant proximate role. Using 38 years of satellite-based inundation maps and hydroclimate data from 109 catchments, we find that annual wetland inundation extent explains interannual runoff and high-flow variability more strongly than any annual or intra-annual climate index in 69% of catchments. Climate, especially snow persistence, affects wetland inundation extent, but wetland inundation exerts a stronger net control on runoff and ultimately sets the pace of annual runoff through fill–spill hydrology. Catchments exhibit wetland inundation–runoff relationships ranging from linear to strongly threshold-like, with threshold-like behavior predominant—particularly where Geographically Isolated Wetlands are abundant. These findings reveal wetlands as active regulators of ecosystem water balance and provide a landscape-explicit basis for forecasting, conservation, and adaptive water management across the region.