The Indian monsoon, a seasonal event that brings key moisture to an agricultural region where about 20 percent of the world's population resides, is getting more extreme, researchers report.

A new study released yesterday in the journal Nature Climate Change found that extreme wet and dry spells within the monsoon period have increased since 1980.

"In the most fundamental sense, we are identifying climate change," said study co-author Noah Diffenbaugh, a Stanford University researcher and fellow at the Woods Institute for the Environment.

"The question is what is causing that climate change. It could be global warming; it could be some other forcing factors," Diffenbaugh added.

Deepti Singh, the lead author of the study and a doctoral candidate in the Environmental Earth System Science program at Stanford, said changes in the monsoon are important, because farmers there are very dependent on rain-fed agriculture for food production both nationally and for export.

"So any changes and any impact on the crops locally can influence local as well as global food security," Singh said.

Although it has been previously documented that overall monsoon rainfall has lessened, few researchers have found changes in extremes.

The frequency and intensity of extreme events within the monsoon are important, as periods of intense rainfall can lead to floods, while periods of extreme dryness can lead to crop failures, particularly at certain growth states when crops are particularly vulnerable.

"A lot of farmers have lost their entire crop yield because of dry spells or just poor weather," Singh said.

Impetus for government planning
For the study's purposes, an extreme wet or dry period was defined as three or more consecutive days of extremely high or low rainfall. The scientists were able to look at precipitation observations from 1951 to 2011 and document these changes in extremes in the period from 1981 to 2011.

Overall, they found that wet spells became more intense in the 1981-2011 period and that dry spells became more frequent but less intense.

"What really gave us some unique capabilities to try to ask those questions in a really objective way was a collaboration with Bala Rajaratnam and his group who are very expert in advanced statistical techniques," Diffenbaugh said.

As the climate changes, studies have pointed to the idea that dry spells increase in frequency and wet spells increase in intensity, although there is not a consensus about what will happen to the Indian monsoon, Singh said.

However, knowing that the monsoon climate has changed could help the Indian government create ways to aid farmers who might be hurt by changes in the monsoon, said Singh, who plans to present this research in India over the summer.

"I think the most actionable way to think about these results is within the context of climate risk management," Diffenbaugh added.

The next step for the research group is to try to identify causes behind the shift in monsoonal climate. Some likely factors may be an increase in aerosols, land-use change or the increase in greenhouse gases.

"What we will do next is try to formally test each of these," Diffenbaugh said.

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC., 202-628-6500