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Air Pollution May Reduce Rainfall and Cause Drought

By August 19, 2009

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As if there weren't already plenty of reasons to cut back on air pollution, now it looks as though cleaner air may reduce drought.

New research by the U.S. Department of Energy’s Pacific Northwest National Laboratory makes a strong case that air pollution is contributing to drought conditions and potential crop failure in northern China by reducing the type of light rainfall that is essential for agriculture.

According to the study, published in the Journal of Geophysical Research, air pollution reduced the number of days of light rainfall in China by 23 percent between 1956 and 2005. Light rainfall is defined as anything up to 0.4 inches (10 millimeters) in a day.

The way this works is that air pollution causes tiny air particles called aerosols—some aerosols also occur naturally—which affect how rain clouds form. Although the number of water droplets in clouds is higher when more aerosols are present, the water droplets in polluted skies are up to 50 percent smaller than in clean air. Many are so small that they are unable to fall as rain.

The research study shows that most of the aerosols in China are caused by human activity, such as the use of fossil fuels. China’s population and fossil fuel consumption increased dramatically between 1960 and 2000, and so did the number of aerosols in China’s skies. The result was the significant decrease in light rainfall noted in the study, and more drought in northern China. Heavy rainfall, which actually increased in some parts of southern China during the same period, can cause flooding and wash away crops before they have a chance to ripen and be harvested.

The conclusion of the researchers is that reducing air pollution in China could help to relieve drought, as well as decreasing acid rain and health problems associated with air pollution. About 2.5 million hectares of crops in northern China and Inner Mongolia are currently threatened by drought, raising concerns that the autumn grain harvest (which accounts for more than 70 percent of China’s total grain crop) could be ruined.

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August 20, 2009 at 7:56 am
(1) guidoLaMoto says:

The correlation is there & the theory is plausible, but is it the coal dust or airborne soil from poor farming practices (or both)? China has a severe soil erosion problem: http://ngm.nationalgeographic.com/2008/09/soil/mann-text/9

March 29, 2010 at 7:57 am
(2) A Chinese says:

It seems plausible that the effect of aerosols on the drought problem explained by the classical nucleation-growth theory. However, how could this explain the excessive rains in the North part of China which happens as the same time??

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