The Earth's wettest regions are likely to get wetter while the most arid will get drier due to warming of the atmosphere caused by increased levels of carbon dioxide, according to a new NASA analysis of more than a dozen climate models.
Scientists ran simulations of 14 different models, starting with CO2 concentrations at about 280 parts per million, which is similar to preindustrial levels but well below the 400 parts per million today. The amount of carbon dioxide was then bumped up by 1 percent per year, an increase that is consistent with a "business as usual" trajectory described by the U.N. Intergovernmental Panel on Climate Change, or IPCC, NASA says.
You can see a video of a composite of the simulations here. Taken as a whole, they show that for every 1 degree Fahrenheit of CO2 warming, heavy rainfall increases by about 4 percent. Total global rainfall remains unchanged because the more frequent occurrence of heavy rainfall in some areas is offset by less frequent moderate rainfall elsewhere, according to the study set for publication in the peer-reviewed Geographical Research Letters.
William Lau, a lead author of the study from NASA's Goddard Space Flight Center, says his research shows that "the global water cycle undergoes a gigantic competition for moisture resulting in a global pattern of increased heavy rain, decreased moderate rain and prolonged droughts in certain regions."
The equatorial Pacific Ocean and parts of Asia subject to monsoonal rains, already among the world's wettest, can expect more heavy rainfall, while the deserts of the U.S. Southwest, Mexico, North Africa, the Middle East, Pakistan and northwest China are most likely to receive even less rainfall.
"In the Southern Hemisphere, drought becomes more likely in South Africa, northwestern Australia, coastal Central America and northeastern Brazil," NASA's website says.
According to the models, for every degree Fahrenheit of warming, the periods with no rain at all will increase by 2.6 percent.