Snow Drought Impacts on GPP Anomalies Across Ecoregions of the Northern Hemisphere

Snow is critical for many ecosystems across the Northern Hemisphere, as snowmelt provides a reliable water supply during spring. However, the increasing frequency of snow droughts, defined by reduced or absent winter snow accumulation, poses a growing threat to soil moisture recharge and consequently, to terrestrial ecosystem functioning. Snow droughts are commonly quantified by reductions in snow water equivalent (SWE), which represent the amount of water stored in the snowpack. Reduced SWE limits soil water recharge during melt, leading to soil moisture deficits that can persist into the growing season, diminish late-season water availability and ultimately reducing plant productivity.Despite their importance, the impacts of snow droughts on the terrestrial carbon cycle remain poorly understood, particularly with respect to gross primary productivity (GPP). Moreover, interactions between snow droughts, soil moisture and precipitation during the growing season, and their potential to amplify or offset ecosystem impacts are largely unknown.Here, we investigate how and where snow droughts have adversely impacted GPP across various ecoregions of the Northern Hemisphere over the past decades. Using the LPJmL dynamic global vegetation model and observational, gridded snow and GPP products, we attribute summer GPP anomalies to snow droughts and identify a wide range of ecoregions where snow droughts both directly reduce GPP and amplify productivity losses when occurring in combination with low spring precipitation.This research advances understanding the feedback mechanism across seasons between snow, soil moisture, and vegetation productivity, providing new insights into ecosystem vulnerability under a changing climate.