More rain in river basins with deficit water: Study

Aditi Tandon

Tribune News Service

New Delhi, July 28

Researchers from the Indian Institute of Technology-Madras and Indian Institute of Technology-Bombay have studied rainfall patterns during the monsoon period over the past century and found that traditional notions of dry areas getting drier and wet areas getting wetter from climate change don’t hold good any more.

“Until now we have believed that climate change is causing the oceans to dry up which means dry areas are experiencing drier spells and wet areas are getting wetter. Our study of the Indian monsoon data doesn’t support this notion,” Prof Sachin Gunthe of IIT-Madras said.

The study is crucial as the government embarks on ambitious river-linking projects. “We show that the amount of rains has decreased in river basins with surplus water and has increased in basins with deficit water. River-linking initiatives have to keep new evidence in mind for long-term results,” Gunthe says.

The study could serve as a launch pad for future scientific investigations into the causes of regional vagaries of rainfall. The study was held in the midst of the monsoon growing more unpredictable than before. Extreme events like floods in Kerala and ongoing zero-water situation in the adjoining state of Tamil Nadu stand testimony to the recent vagaries of the monsoon.

IIT-Madras and IIT-Bombay collaboration sought to understand the nature of variations in monsoon rainfall and the impacts of climate change on rainfall patterns through an analysis of historic data and simulation studies. The researchers used IMD’s daily rainfall data from 1901 to 2004.

“Our recommendation is that concerted approaches based on our observations would benefit national-scale climate-water adaptation and regional preparedness,” says Subimal Ghosh of IIT-Bombay, a researcher author.

It is common knowledge that geographic variation of extremes in rainfall occurs due to convection — the movement of moisture-laden hot air upwards followed by cooling at higher altitudes and shedding of the moisture as rain. Convection-based rains would mean that regions where there is excess moisture in the air should experience more rainfall. “This, however, was not seen in the rainfall pattern we analysed,” Ghosh says.

“These insights are critical not only for understanding variations in seasonal rainfall in India but also for framing long-term water management policies.”

In other direction

New findings contradict common knowledge that dry areas are becoming drier and wet areas are getting wetter in response to climate change, offer insights for long-term water management policies