Increases in air pollution and other particulate matter in the atmosphere can strongly affect cloud development in ways that reduce precipitation（沉淀，冰雹） in dry regions or seasons, while increasing rain, snowfall and the intensity of severe storms in wet regions or seasons, says a new study by a University of Maryland-led team of researchers. The research provides the first clear evidence of how aerosols（悬浮颗粒） -- 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.

"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 Maryland and lead author of the study.

The study found that under very dirty conditions, the mean cloud height of deep convective clouds（对流云） 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 Maryland's 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 study by Li and co-authors Feng Niu and Yanni Ding, also of the University of Maryland; Jiwen Fan of Pacific Northwest National Laboratory; Yangang Liu of Brookhaven National Laboratory, Upton, NY; and Daniel Rosenfeld of the Hebrew University of Jerusalem, is published in the Nov. 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（证明） 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（廉价出售） 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.