air pollution

Polluted air makes droughts, floods worse

U. MARYLAND (US) — Rising air pollution can strongly affect cloud formation in a way that can make floods and droughts even worse, a new study finds.

The research provides the first clear evidence of how aerosols—soot, dust, and other small particles in the atmosphere—can affect weather and climate; and the findings have important implications for the availability, management and use of water resources in regions across the United States and around the world, say the researchers and other scientists.

See larger version. (Credit: University of Maryland)


“Using a 10-year dataset of extensive atmosphere measurements from the U.S. Southern Great Plains research facility in Oklahoma (run by the Department of Energy’s Atmospheric Radiation Measurement program)—we have uncovered, for the first time, the long-term, net impact of aerosols on cloud height and thickness, and the resultant changes in precipitation frequency and intensity,” says Zhanqing Li, a professor of atmospheric and oceanic science at the University of Maryland and the study’s lead author.

The study found that under very dirty conditions, the mean cloud height of deep convective clouds is more than twice the mean height under crystal clean air conditions. “The probability of heavy rain is virtually doubled from clean to dirty conditions, while the chance of light rain is reduced by 50 percent,” says Li, who is also affiliated with Beijing Normal University.

The scientists obtained additional support for these findings with matching results obtained using a cloud-resolving computer model. The findings are reported in the November 13 issue of Nature Geoscience.

“These new findings of long-term impacts, which we made using regional ground measurements, also are consistent with the findings we obtained from an analysis of NASA’s global satellite products in a separate study. Together, they attest to the needs of tackling both climate and environmental changes that matter so much to our daily life,” says Li.

“Our findings have significant policy implications for sustainable development and water resources, especially for those developing regions susceptible to extreme events such as drought and flood.

“Increases in manufacturing, building of power plants and other industrial developments, together with urbanization, are often accompanied with increases in pollution whose adverse impacts on weather and climate, as revealed in this study, can undercut economic gains,” he stresses.

Tony Busalacchi, chair of the Joint Scientific Committee, World Climate Research Program notes the significance of the new findings. “Understanding interactions across clouds, aerosols, and precipitation is one of the grand challenges for climate research in the decade ahead, as identified in a recent major world climate conference.

“Findings of this study represent a significant advance in our understanding of such processes with significant implications for both climate science and sustainable development,” says Busalacchi, who also is professor and director of the University of Maryland Earth System Science Interdisciplinary Center.

“We have known for a long time that aerosols impact both the heating and phase changes (condensing, freezing) of clouds and can either inhibit or intensify clouds and precipitation,” says Russell Dickerson, a professor of atmospheric and oceanic science at Maryland. “What we have not been able to determine, until now, is the net effect. This study by Li and his colleagues shows that fine particulate matter, mostly from air pollution, impedes gentle rains while exacerbating severe storms. It adds urgency to the need to control sulfur, nitrogen, and hydrocarbon emissions.”

According to climate scientist Steve Ghan of the Pacific Northwest National Laboratory, “This work confirms what previous cloud modeling studies had suggested, that although clouds are influenced by many factors, increasing aerosols enhance the variability of precipitation, suppressing it when precipitation is light and intensifying it when it is strong.

“This complex influence is completely missing from climate models, casting doubt on their ability to simulate the response of precipitation to changes in aerosol pollution.”

The Department of Energy, NASA, the National Science Foundation, and the Chinese Ministry of Science and Technology supported the work.

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