Justin Mankin, a former postdoctoral fellow in the Paleodynamics Lab, has published a paper in Nature Geosciences on the role of plants in future freshwater availability. Plants are expected to generate more global-scale runoff under increasing atmospheric carbon dioxide concentrations by reducing evapotranspiration. Recent studies using Earth System Models from phase 5 of the Coupled Model Intercomparison Project ostensibly reaffirm this result, further suggesting that plants will ameliorate the dire reductions in water availability projected by other studies. Justin's work complicates this narrative by showing that projected plant responses directly reduce future runoff across vast swaths of North America, Europe and Asia because of additional vegetation growth and longer and warmer growing seasons. These runoff declines occur despite reductions in evapotranspiration and the efficiency with which plants use water, even in regions with increasing or unchanging precipitation. These results are strengthened even further when the model results are constrained using regional-scale observations of evapotranspiration. The main conclusion of the work is that terrestrial vegetation plays a large and unresolved role in shaping future regional freshwater availability, one that will not ubiquitously ameliorate future warming-driven surface drying.
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