Early snowpack disappearance and warm-season ecosystem water use

Reduced spring snowpacks in the mid- and high-latitudes will have ecohydrological responses that could impact warm-season water availability. Recent work has shown that the earlier disappearance of spring snow, coupled with higher temperatures and CO2 concentrations, will shift vegetation phenology and primary production. These changes in plant growth may increase bulk ecosystem water use despite anticipated increases in leaf-level water use efficiency, amplifying warm-season drought risks. Despite a crucial role for snow in shaping warm-season water availability in some regions, we lack a robust observational constraint on how ecosystem water use responds to the timing of snow cover departure across hydroclimatic gradients. Here we use in situ measurements of snow cover and vegetation water fluxes from eddy covariance networks to determine the effects of the timing of snow disappearance on the warm-season water balance across a range of ecosystems and hydroclimatic regimes. We further attempt to identify the causal pathways in the snow-vegetation-warm season drought continuum by process tracing the hydrological and radiative mechanisms through which snow influences growing season conditions. Our findings shed light on the risks to human and natural systems posed by future shrinking snow seasons.