Southern India has grown wetter over seven decades, finds IMD study

Southern India has become wetter over the past seven decades, as the area classified as having a hot semi-arid climate has nearly halved from about 30% to 16% of the peninsula between 1951-1980 and 1991-2020, according to a study by scientists from the India Meteorological Department (IMD) and the Indian Institute of Tropical Meteorology (IITM), Pune.

Published in MAUSAM, the IMD’s peer-reviewed journal, the study found that much of the peninsula’s hot semi-arid regions had transitioned into the tropical savannah climate zone, which receives more rainfall and has a prolonged dry season.

This zone now covers nearly three-fourths of peninsular India, compared with about three-fifths in the 1950s. The study, titled ‘Identifying the climate zones shifts of Indian meteorological subdivisions: insights from historical records’, uses the Köppen-Geiger climate classification system to assess changes across India’s meteorological subdivisions.

North-west India gets drier, hotter

The researchers mapped India’s climate zones across successive 30-year periods, using the IMD’s rainfall and temperature observations from 1951 to 2020. They found that most of the shift in southern India had occurred during the two most recent periods, 1981-2010 and 1991-2020, primarily because of an increase in rainfall.

The trend in southern India contrasts with that in north-west India, where the hot semi-arid zone has expanded from western to eastern Uttar Pradesh amid declining rainfall. Day- and night-time temperatures, meanwhile, have increased across the country.

Farm impact

The researchers said changes in climate zones could have implications for agriculture, particularly in determining suitable crops and sowing periods. They stressed the need to monitor these shifts and incorporate them into long-term agricultural planning.

This year, the IMD’s Regional Meteorological Centre in Chennai declared the onset of the northeast monsoon on October 15, 2026, five days ahead of its normal date. The IMD has forecast a normal northeast monsoon for Tamil Nadu, against the seasonal average of 44 cm. While the Cauvery delta and southern districts are likely to receive normal to above-normal rainfall, the north interior districts are expected to receive below-normal rainfall.

Tamil Nadu ended the June-September southwest monsoon with a 20% rainfall deficit. The country as a whole recorded a 12.6% deficit during the season, as El Niño conditions contributed to the weakening of the southwest monsoon.

Ananya Karmakar of IMD Pune, the lead author of the study, said the long-term increase in rainfall over the peninsula was an important factor to consider in water and agricultural planning in Tamil Nadu, given the State’s dependence on the northeast monsoon.

Mrutyunjay Mohapatra, IMD’s Director-General of Meteorology and a co-author of the study, said the department’s seasonal forecasts and advisories to farmers took into account both long-term climate trends and seasonal variations.