Western Ghats can contribute up to 30% of rainfall in Bengaluru: Study

The lush forests and towering hills of the Western Ghats not only play an important role in capturing and storing rainwater, but are also crucial to the amount of rain falling in Bengaluru and other neighbouring areas.

The implication that the Western Ghats play a role in the strength of the rainfall, however, does not seem to have percolated to policy. File photo

In the three months that the Southwest monsoon lashes the subcontinent, evaporation from land masses can contribute up to 30 per cent of the rainfall received, reveals a study by researchers from the Centre for Earth Sciences (CEaS) and Divecha Centre for Climate Change at the Indian Institute of Science, Bengaluru.

The team — led by professor Prosenjit Ghosh — sought to gauge the composition of the rain in the city through isotopes of oxygen and hydrogen. The quantities of these isotopes vary in the ocean and land, and their composition in the rainfall can give an indication to the source of the rain.

How nature works

Unsurprisingly, the phenomenon of oceans heating up during Indian summers — and the associated complications of El Nino and other global weather phenomena — leads to much of the moisture during the monsoon. However, as the swirls of wind and cloud make their way inland, they pick up evaporation and moisture of the rainforests, vegetation and inland waterbodies.

“There is recycling over time and this makes a significant contribution to the rainfall as the monsoon progress inlands and loses some of the oceanic contribution,” says Prof. Ghosh. This contribution, find the researchers, is between 20 and 30 per cent of the total rainfall.

For the Northeast monsoon, when moisture is picked up from the Bay of Bengal, the patches of green in the Eastern Ghats similarly contribute to the rainfall here.

Explaining the importance of the research, Prof. Ghosh says, “In the West, this sort of research plays a role in policymaking to gauge the effects of urbanisation and how best to deal with landmass changes owing to expanding cities.”

The implication that the Western Ghats play a role in the strength of the rainfall does not seem to have percolated to policy. The 2015 Forest Survey of India report had shown that a disheartening 173 sq. km of forest land had reduced in the eight districts of Karnataka through which the mountain chain runs.