Glacial drought buffering through the 21st century

Global climate model projections suggest that 21st century climate change will bring significant drying in the terrestrial midlatitudes. Recent glacier modeling suggests that runoff from glaciers will continue to provide substantial freshwater in many drainage basins, though the supply will generally diminish throughout the century. In the absence of dynamic glacier ice within global climate models (GCMs), a comprehensive picture of future drought conditions in glaciated regions has been elusive. We evaluate glacial buffering of droughts in the Standardized Precipitation-Evapotranspiration Index (SPEI), which we calculate by combining CMIP5 climate model output with glacial runoff projections from GloGEM.

We find that accounting for glacial runoff tends to increase multi-model ensemble mean SPEI (wetter baseline) and reduce drought frequency and severity, even in basins with glacier cover of <2% by area.  We also find that the strength and future trend of glacial drought buffering depends on basin aridity index and glacial cover, and does not depend on other characteristics such as total basin area or latitude.  Glacial drought buffering persists even as glacial runoff is projected to decline through the 21st century.