Snow Accumulation Regimes During Nuclear Winter

Nuclear winter, caused by stratospheric soot injection after a nuclear conflict, would cause sustained cooling lasting years to over a decade. This cooling shifts precipitation from rain to snow and suppresses snowmelt, with largely unexplored consequences for snow storage and runoff. We force a global temperature-index snow model with climate simulations of three nuclear war scenarios (16, 47, and 150 Tg soot) and analyze runoff in six major river basins. Global snow storage peaks four to six years after the injection and remains slightly above control levels after 15 years. Three regional patterns emerge: new seasonal snowpacks, prolonged snow seasons, and multi-year accumulation at high latitudes. Larger snowpacks raise spring runoff peaks in the Rhine and Tigris-Euphrates, while high-latitude accumulation suppresses snowmelt elsewhere. These shifts would increase the potential for spring floods and prolonged low flows, affecting drinking water supply and irrigation.