Causes of Missing Snowmelt Following Drought

Water management in snowy mountainous regions hinges on forecasting snowmelt runoff. However, droughts are altering snowpack-runoff relationships with ongoing debate about the driving mechanisms. For example, 2021 California, less than half of predicted streamflow arrived. Mechanisms proposed for this “missing” included changes evapotranspiration (ET), rainfall, and subsurface moisture conditions. Here, we demonstrate that ET drought years generates dry conditions reduce runoff subsequent years. A model including legacy depleted storage reduced median error forecasts from 60% to 20% at 15 minimally disturbed basins 18% 2% 6 water supply Sierra Nevada (basins range area 5 23,051 km2 mean annual precipitation 814 1,549 mm). Our findings indicate relationship between snowpack will evolve as plant ecosystems respond climate change alter dynamics.