Global warming could delay, weaken monsoons: study

Yahoo News 1 Mar 09;

CHICAGO (AFP) – Global warming could delay the start of the summer monsoon by five to 15 days within the next century and significantly reduce rainfall in much of South Asia, a recent study has found.

Rising global temperatures will likely lead to an eastward shift in monsoon circulation which could result in more rainfall over the Indian Ocean, Myanmar and Bangladesh but less over Pakistan, India and Nepal, the study found.

It could also result in longer delays between rainy seasons and intensify the risk of deadly floods by leading to a significant increase in average rainfalls in some coastal areas of western India, Sri Lanka and Myanmar.

That could have a major impact on agriculture, human health and the economies of the region, warned study author Noah Diffenbaugh.

"Almost half of the world's population lives in areas affected by these monsoons, and even slight deviations from the normal monsoon pattern can have great impact," said Diffenbaugh, interim director of Purdue University's Climate Change Research Center.

"Agricultural production, water availability and hydroelectric power generation could be substantially affected by delayed monsoon onset and reduced surface runoff."

The atmospheric conditions that lead to reduced rain also can lead to intensification of extremely hot conditions, said lead author Moetasim Ashfaq, a graduate student at Purdue.

"In the past when we have seen extremely hot days, we have observed a similar circulation anomaly," Ashfaq said in a statement.

"These circulation changes decrease moisture flow over the land, and we see longer periods without rain, along with hot conditions."

Ashfaq used a high-resolution climate model to map how global warming will affect the complex topography of South Asia by recreating the monsoon season of past years.

He found that increasing temperatures strengthen some aspects of large-scale monsoon circulation but weaken the fine-scale interactions of the land with the moisture in the atmosphere.

"Even with a strong monsoon system, if circulation changes enough to change where and when rain is delivered, then that could have an impact that has not been captured in the large-scale evaluations," Ashfaq said.

The study was published in the January issue of the peer-reviewed journal Geophysical Research Letters.