Krista A. Dunne
Paul C.D. Milly
2016
<p><span>By various measures (drought area</span><span> and intensity</span><span>, climatic aridity index</span><span>, and climatic water deficits</span><span>), some observational analyses have suggested that much of the Earth</span><span class="mb">’</span><span>s land has been drying during recent decades, but such drying seems inconsistent with observations of dryland greening and decreasing pan evaporation</span><span>. ‘Offline</span><span class="mb">’</span><span> analyses of climate-model outputs from anthropogenic climate change (ACC) experiments portend continuation of putative drying through the twenty-first century</span><span>, despite an expected increase in global land precipitation</span><span>. A ubiquitous increase in estimates of potential evapotranspiration (PET), driven by atmospheric warming</span><span>, underlies the drying trends</span><span>, but may be a methodological artefact</span><span>. Here we show that the PET estimator commonly used (the Penman–Monteith PET</span><span> for either an open-water surface</span><span> or a reference crop</span><span>) severely overpredicts the changes in non-water-stressed evapotranspiration computed in the climate models themselves in ACC experiments. This overprediction is partially due to neglect of stomatal conductance reductions commonly induced by increasing atmospheric CO</span><sub>2</sub><span> concentrations in climate models</span><span>. Our findings imply that historical and future tendencies towards continental drying, as characterized by offline-computed runoff, as well as other PET-dependent metrics, may be considerably weaker and less extensive than previously thought.</span></p>
application/pdf
10.1038/nclimate3046
en
Nature
Potential evapotranspiration and continental drying
article