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How Rising CO2 Concentrations will change Global Rainfall Types

May 06, 2013; 2:37 PM

A new, computer modeling study led by NASA shows for the first time how rising CO2 concentrations could affect the entire range of rainfall types for the globe.

The research team looked at 14 climate model simulations that spanned 140-year periods that begin when CO2 concentrations were at pre-industrial levels (~280 ppm) followed by an increase of 1 percent per year.

Model simulations spanning 140 years show that warming from carbon dioxide will change the frequency that regions around the planet receive no rain (brown), moderate rain (tan), and very heavy rain (blue). The occurrence of no rain and heavy rain will increase, while moderate rainfall will decrease. Animation courtesy of NASA's Goddard Space Flight Center Scientific Visualization Studio and YouTube.

The team found that the wetter regions of the world, such as the equatorial Pacific and the Asian Monsoon regions will see increases in heavy precipitation, while regions with moderate and little rainfall could become drier.

For every one degree F. of CO2-induced warming, heavy rainfall will increase globally by 3.9 percent and light rain will increase by 1.0 percent. Moderate rainfall will decrease by 1.4 percent, which means that there will be little change in total global rainfall.

The models also projected that there will be a 2.6 percent global increase in the length of periods with no rainfall for every degree F. of warming. In the Northern Hemisphere, areas most likely to be affected include the deserts and arid regions of the southwest United States, Mexico, North Africa, the Middle East, Pakistan, and northwestern China.

Key excerpt from the NASA story.......

Analyzing the model results, William Lau and his co-authors calculated statistics on the rainfall responses for a 27-year control period at the beginning of the simulation, and also for 27-year periods around the time of doubling and tripling of carbon dioxide concentrations. They conclude the model predictions of how much rain will fall at any one location as the climate warms are not very reliable.

"But if we look at the entire spectrum of rainfall types we see all the models agree in a very fundamental way -- projecting more heavy rain, less moderate rain events, and prolonged droughts," Lau said.

The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com

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