Characterizing runoff response to rainfall in permafrost catchments and its implications for hydrological and biogeochemical fluxes in a warming climate

Abstract. Understanding how Arctic catchments respond to rainfall is critical for anticipating hydrological and biogeochemical effects of a warming climate. We use ensemble rainfall-runoff analysis (ERRA) to identify how runoff response to rainfall varies with meteorological, subsurface, and geomorphic conditions across three permafrost catchments: Upper Kuparuk (Alaska) and the Goose and Ptarmigan catchments (Cape Bounty, Canadian High Arctic). ERRA enables us to quantify event-scale runoff responses to rainfall using high-resolution, multi-year hydrometeorological datasets, and test how variations in rainfall intensity, thaw depth, antecedent wetness, and active layer detachments (ALDs) affect runoff behavior. Our results show that peak runoff response increases by more than five-fold in response to increases in antecedent streamflow (a proxy for antecedent moisture), and is also higher in summers with higher average precipitation. By contrast, warmer winters and springs, likely linked to deeper thaw and increased subsurface storage capacity, are associated with reduced runoff sensitivity to rainfall. Furthermore, a paired watershed comparison shows that streamflow and riverine fluxes of dissolved solids, suspended sediment, and particulate organic carbon are more readily mobilized by rainfall inputs when ALDs are present. Considered together, these findings highlight the difficulty in generalizing climate-driven runoff trends in permafrost regions subject to competing and interacting controls, such as precipitation intensity, storage capacity and permafrost stability. Our findings offer a more nuanced alternative to broad classifications of Arctic landscapes as “drying” or “wetting” under climate change.