Forest Impacts on Peak Runoff Revealed by Accounting for the Effects of Climate

Abstract Land cover affects the runoff response of catchments. However, such land‐cover effects remain difficult to decipher because experimental studies are site‐specific, while large‐sample analyses are often confounded by climate gradients that obscure the role of land cover. Site‐to‐site comparisons that ignore differences in antecedent wetness may overestimate runoff responses in forested catchments because they are typically found in humid climates. Here we quantify runoff responses to unit precipitation inputs and examine how they vary across 252 U.S. catchments with different land covers and forest fractions. For comparable antecedent wetness conditions (as quantified by antecedent streamflow), peak runoff responses decline as forest cover increases, with peak responses in forested catchments being 16%–63% lower than in catchments dominated by cropland or grassland. By accounting for climate‐driven differences among catchments, our approach isolates the influences of land cover on reducing peak flows, which are often masked by climate in large‐sample analyses.