By various measures (drought area1 and intensity2, climatic aridity index3, and climatic water deficits4), some observational analyses have suggested that much of the Earth’s land has been drying during recent decades, but such drying seems inconsistent with observations of dryland greening and decreasing pan evaporation5. ‘Offline’ analyses of climate-model outputs from anthropogenic climate change (ACC) experiments portend continuation of putative drying through the twenty-first century3,6,7,8,9,10, despite an expected increase in global land precipitation9. A ubiquitous increase in estimates of potential evapotranspiration (PET), driven by atmospheric warming11, underlies the drying trends4,8,9,12, but may be a methodological artefact5. Here we show that the PET estimator commonly used (the Penman–Monteith PET13 for either an open-water surface1,2,6,7,12 or a reference crop3,4,8,9,11) 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 CO2 concentrations in climate models5. 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.
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Dai, A. Characteristics and trends in various forms of the Palmer Drought Severity Index during 1900–2008. J. Geophys. Res. 116, D12115 (2011).
Sheffield, J., Wood, E. F. & Roderick, M. L. Little change in global drought over the past 60 years. Nature 491, 435–438 (2012).
Feng, S. & Fu, Q. Expansion of drylands under a warming climate. Atmos. Chem. Phys. 13, 10081–10094 (2013).
McCabe, G. J. & Wolock, D. M. Increasing Northern Hemisphere water deficit. Climatic Change 132, 237–249 (2015).
Roderick, M. L., Greve, P. & Farquhar, G. D. On the assessment of aridity with changes in atmospheric CO2 . Wat. Resour. Res. 51, 5450–5463 (2015).
Burke, E. J., Brown, S. J. & Christidis, N. Modeling the evolution of global drought and projections for the twenty-first century with the Hadley Centre climate model. J. Hydrometeor. 7, 1113–1125 (2006).
Dai, A. Increasing drought under global warming in observations and models. Nature Clim. Change 3, 52–58 (2012).
Cook, B. I., Smerdon, J. E., Seager, R. & Coats, S. Global warming and 21st century drying. Clim. Dyn. 43, 2607–2627 (2014).
Fu, Q. & Feng, S. Responses of terrestrial aridity to global warming. J. Geophys. Res. Atmos. 119, 7863–7875 (2014).
Scheff, J. & Frierson, D. M. W. Terrestrial aridity and its response to greenhouse warming across CMIP5 climate models. J. Clim. 28, 5583–5600 (2015).
Scheff, J. & Frierson, D. M. W. Scaling potential evapotranspiration with greenhouse warming. J. Climate 27, 1539–1558 (2014).
Dai, A. Drought under global warming: a review. WIREs Clim. Change 2, 45–65 (2011).
Shuttleworth, W. J. Handbook of Hydrology (ed. Maidment, D. R.) Ch. 4 (McGraw-Hill, 1993).
Shuttleworth, W. J. & Wallace, J. S. Evaporation from sparse crops—an energy combination theory. Q. J. R. Meteorol. Soc. 111, 839–855 (1985).
Budyko, M. I. Climate and Life (Academic, 1974).
Roderick, M. L., Sun, F., Lim, W. H. & Farquhar, G. D. A general framework for understanding the response of the water cycle to global warming over land and ocean. Hydrol. Earth Syst. Sci. 18, 1575–1589 (2014).
Koster, R. D. & Mahanama, S. P. P. Land surface controls on hydroclimatic means and variability. J. Hydrometeor. 13, 1604–1620 (2012).
Schewe, J. et al. Multimodel assessment of water scarcity under climate change. Proc. Natl Acad. Sci. USA 111, 3245–3250 (2014).
Chiew, F. H. S., Whetton, P. H., McMahon, T. A. & Pittock, A. B. Simulation of the impacts of climate change on runoff and soil moisture in Australian catchments. J. Hydrol. 167, 121–147 (1995).
Milly, P. C. D., Dunne, K. A. & Vecchia, A. V. Global pattern of trends in streamflow and water availability in a changing climate. Nature 438, 347–350 (2005).
Cook, B. I., Ault, T. R. & Smerdon, J. E. Unprecedented 21st century drought risk in the American Southwest and Central Plains. Sci. Adv. 1, e1400082 (2015).
Sherwood, S. & Fu, Q. A drier future? Science 343, 737–739 (2014).
Milly, P. C. D. & Dunne, K. A. Macroscale water fluxes 2. Water and energy supply control of their interannual variability. Wat. Resour. Res. 38, 24-1–24-9 (2002).
Allen, R. G., Periera, L. S., Raes, D. & Smith, M. Crop Evapotranspiration—Guidelines for Computing Crop Water Requirements Irrigation and Drainage Paper 56, 15 (Food and Agricultural Organization of the United Nations, 1998).
The World Climate Research Programme’s Working Group on Coupled Modelling is responsible for CMIP; the climate modelling groups listed in Supplementary Table 1 produced, and made available, their model output. For CMIP, the US Department of Energy’s Program for Climate Model Diagnosis and Intercomparison provides coordinating support and led development of software infrastructure in partnership with the Global Organization for Earth System Science Portals. A. Berg, S. Kapnick, M. Roderick, J. Scheff and G. Wang gave helpful reviews of our manuscript.
The authors declare no competing financial interests.
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Milly, P., Dunne, K. Potential evapotranspiration and continental drying. Nature Clim Change 6, 946–949 (2016) doi:10.1038/nclimate3046
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