Abstract
The Budyko framework consists of a curvilinear relationship between the
evaporative ratio (i.e., actual evaporation over precipitation) and the
aridity index (potential evaporation over precipitation) and defines
evaporation’s water and energy limits. A basin’s movement within the
Budyko space illustrates its hydroclimatic change and can help identify
the main drivers of change. Basins are expected to move along their
Budyko curves when only long-term changes in the aridity index drive
changes in the evaporative ratio. We hypothesize that the increasing
effects of global warming on the hydrological cycle will cause basins to
move along their Budyko curves. To test our hypothesis, we quantify the
movement in Budyko space of 353 river basins from 1901 to 2100 based on
the outputs of nine models from the Coupled Model Intercomparison
Project - Phase 5 (CMIP5). We find that significant increases in
potential evaporation due to global warming will lead to basins moving
primarily horizontally in Budyko space accompanied by minor changes in
the evaporative ratio. However, 37% of the basins will still deviate
from their Budyko curve trajectories, with less evaporation than
expected by the framework. We elaborate on how land-use change,
vegetation changes, or shifts in precipitation or snow to rain ratios
can explain these deviations.