A new publication in Nature Climate Change puts the brakes on predictions that global warming/climate change may produce continental scale droughts into the late 21st century. For example, NCAR said in 2010: CLIMATE CHANGE: DROUGHT MAY THREATEN MUCH OF GLOBE WITHIN DECADES

Then they had to back down and correct the original, when they found the drought PDSI (Palmer Drought Severity Index) numbers were overestimated by double the amount:

Update – July 3, 2012 This news release has been revised to reflect a miscalculation in the original study that inadvertently resulted when simulations of historical drought were combined with simulations of future drought. The revised maps, below, indicate that drought levels on the Palmer Drought Severity Index may reach -10 in certain regions, whereas the levels reached -20 on the original maps. Similarly, upper-latitude areas become less moist than previously projected. Large portions of the globe are still expected to experience dryness that is extreme if not unprecedented. For many regions, the corrected data show the movement toward drought taking place about three decades slower than originally projected.

Here is what NCAR says the future drought scenario looks like under climate change over the next 80+ years:

In this new study published this week, it seems that the model predictions just aren’t lining up with observations, such as the recently observed greening of Earth and the measurements of evapotranspiration, which may have an embedded methodological artifact and failure to account for how plant stomata have been responding.

Potential evapotranspiration and continental drying

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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 CO 2 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.

References

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h/t to Dr. Richard Betts

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