Rising temperatures may weaken monsoon season in south Asia

Science Daily: The South Asian summer monsoon - critical to agriculture in Bangladesh, India, Nepal and Pakistan - could be weakened and delayed due to rising temperatures in the future, according to a recent climate modeling study. A Purdue University research group found that climate change could influence monsoon dynamics and cause less summer precipitation, a delay in the start of monsoon season and longer breaks between the rainy periods.

Noah Diffenbaugh, whose research group led the study, said the summer monsoon affects water resources, agriculture, economics, ecosystems and human health throughout South Asia. "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, an associate professor of earth and atmospheric sciences and interim director of the Purdue Climate Change Research Center. "Agricultural production, water availability and hydroelectric power generation could be substantially affected by delayed monsoon onset and reduced surface runoff. Alternatively, the model projects increases in precipitation over some areas, including Bangladesh, which could exacerbate seasonal flood risks." The summer monsoons are responsible for approximately 75 percent of the total annual rainfall in major parts of the region and produce almost 90 percent of India's water supply, he said.

General circulation models have been used for projections of what may happen to monsoon patterns for this region, but the models have disagreed as to whether precipitation will increase or decrease, said Moetasim Ashfaq, lead author of the study and a graduate student in earth and atmospheric sciences at Purdue. "South Asia is a unique region with very complex topography," he said. "It ranges from 0 meters elevation from sea level in the south to more than 5,500 meters from sea level in the north. So in terms of topography playing a role in climate and weather, this region of the world is where we expect to see a large impact. Global models like the ones featured in the Intergovernmental Panel on Climate Change reports can resolve large-scale interactions but have difficulty capturing some of the more subtle atmospheric processes."…

These maps show projected future changes in South Asian summer precipitation and monsoon onset date. A Purdue-led team found that rising future temperatures could lead to less rain and a delay in the start of monsoon season by up to 15 days by the end of the 21st century. (Credit: Diffenbaugh lab image)