PrintMore Floods and Droughts
As noted above, there is a tendency for wet places to get wetter and dry places to get drier, with the subtropical dry zones expanding somewhat. When conditions are right to rain, warmer air holds more water (by roughly 7% per degree C or 4% per degree F), so all else equal, a warmer climate can deliver more rain in a hurry. But, evaporation speeds up with warming, too. All winter, Dr. Alley’s tomato patch is damp or frozen; in the summer, just a week or two after a downpour he needs to water the plants again. A more summer-like world is likely to have more variability in the water cycle, with more floods and more droughts.
Video: Potential for Drought by the End of this Century (1:01)
DR. RICHARD ALEY: This figure comes from the US government, from the Environmental Protection Agency, EPA, and it's based on just a fascinating study that was published in 2011 that takes into account the changes in temperature, evaporation. It takes into account changes in the rainfall that are expected if we keep emitting a lot of CO2 when we look out late in the century. What you see is low risk of drought is expected, so something like over here, in places up near the pole, for example, where not a huge number of people live at this time.
But what you'll notice is the high risk of drought in very big areas where actually a whole lot of people live now. And so this is one of those plots that is maybe a little bit worrisome if you look out to the future and we don't decide to change their behavior. Because there are projections that we make drought more likely in a whole lot of places where a whole lot of people now live.