Glacial runoff buffers drought through the 21st century---but models
disagree on the details
Abstract
Global climate model projections suggest that 21st century climate
change will bring significant drying in the 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 basin-scale water availability for human and ecosystem
services has been elusive. Here, we leverage the results of existing
GCMs and a global glacier model to compute the effect of glacial runoff
on the Standardized Precipitation-Evapotranspiration Index (SPEI), an
indicator of basin-scale water availability. We find that glacial runoff
tends to increase mean SPEI and reduce interannual variability, even in
basins with relatively little glacier cover. However, in many basins we
find inter-GCM spread comparable to the amplitude of the ensemble mean
glacial effect, which suggests considerable structural uncertainty.