The forecast for the future of rainfall on Earth is in: over the next hundred years, areas that receive lots of precipitation right now are only going to get wetter, and dry areas will go for longer periods without seeing a drop, according to a new NASA-led study on global warming. "We looked at rainfall of different types," said William Lau, NASA's deputy director of atmospheric studies and the lead author of the study, in a phone interview with The Verge. "The extreme heavy rain end the prolonged drought side both increase drastically and are also connected physically."

"The new part is looking at the entire global rainfall system."

The NASA rainfall study

study, which is due to be published in an upcoming edition of the journal Geophysical Research Letters, examined data from 14 different leading global climate models. Although each one previously predicted rainfall increases in rain-prone areas such as the tropics, and droughts in drier regions including the American Southwest, the study by Lau and his colleagues is said to be the first to look at rainfall from a global perspective, including over unpopulated areas like the middle of the oceans. "The new part is looking at the entire global rainfall system from a basic science perspective, and what we're finding is amazing" Lau said.

NASA animation showing rainfall projections over a 140 year period. Credit: NASA's Goddard Space Flight Center Scientific Visualization Studio.

Specifically, the new study found that although the 14 climate models differ when it comes to the amount of rainfall in individual locations such as cities, over larger areas, they all point to the same average picture. That is, for every single degree Fahrenheit the global average temperature climbs, heavy rainfall will increase in wet areas by 3.9 percent, while dry areas will experience a 2.6 percent increase in time periods without any rainfall.

"Dust Bowl levels by the end of the century."

"The projected Mediterranean and southwestern US droughts forced by CO2 [carbon dioxide] increases alone exceed Dust Bowl levels by the end of the century," said Dargan Frierson, associate professor of atmospheric sciences at the University of Washington, who was not involved in the study. The reason for the shift is thought to be due to the fact that as the globe warms, the atmosphere is able to hold more water vapor as moisture, but this moisture clusters in the already wet areas, depriving the dry areas of moisture and exacerbating their droughts. Just how quickly the change happens depends on how much CO2 gets pumped into the atmosphere, but Lau said his study was applicable to the next century.