Rainfall to increase over next 100 years, shows IISc paper

Climate model simulation shows role of water vapour in change in quantum of rainfall

A view of rain and monsoon clouds seen from Ramgiri hills near Ramagar which is 45 km in Bangalore on July 14th, 2013. Photo: K. Bhagya Prakash

Increasing temperatures result in increase in water vapour in the atmosphere, which causes an increase in the quantum of rainfall. This answers as to why the Indian monsoon rainfall increased from the last glacial maximum to the present.

With the concentration of carbon dioxide in the atmosphere going up, resulting in more water vapour, rainfall is expected to increase in the next 100 years.

The paper published in

Nature , titled ‘Modulation of Indian monsoon by water vapor and cloud feedback over the past 22,000 years’ has been authored by Chetankumar Jalihal, Jayaraman Srinivasan, and Arindham Chakraborty from the Divecha Centre for Climate Change, Indian Institute of Science.

An excerpt of the paper states that over 22,000 years ago, the monsoon was around 3.3. mm/ day. It then increased to 6.6 mm/ day around 14,000 years ago, and then decreased to 6 mm/ day in the 20th century. The change in monsoon rainfall was attributed to changes in the amount of solar radiation incident on India during the summer monsoon. A simple climate model simulation showed, for the first time, the role of water vapour and clouds in amplifying the effect of solar radiation on monsoon rainfall. The concentration of carbon dioxide in atmosphere has increased from 180 ppm to 280 ppm over the last 22,000 years. This is one of the main causes for increase in water vapour, which has led to the doubling of monsoon rainfall.

Due to anthropogenic activities, the carbon dioxide increased by about 100 ppm in the last 100 years. It will increase further in the near future and the diagnostic model can be used to understand how rainfall will change, the excerpt read.

Prof. Srinivasan told

The Hindu that the study was based on model simulation. “One of the major reasons for the variation in monsoon is the increase in water vapour due to increase in temperature. In the next 100 years, the water vapour is also likely to increase, which will result in increase in rainfall,” he said and added that to understand change in rainfall patterns, it was important to understand the past.