Annual precipitation over Gangetic West Bengal and Bihar fell between 1981 and 2020 (file picture)
The findings, published in the Oct 2026 issue of IMD’s peer-reviewed journal ‘Mausam’, suggest long-term changes in temperature and rainfall are altering the climatic character of entire regions, with implications for agriculture and water and food security. The tropical savannah climate’s share of the northeast has shrunk from 18% between 1951 and 1980 to 12% between 1991 and 2020, while the area classified as temperate expanded from roughly three-fourths to more than four-fifths of the region. Researchers analysed IMD rainfall and temperature data from 1951 to 2020 in successive 30-year periods, revealing a progressive expansion of the temperate category across the northeast. Annual precipitation over Gangetic West Bengal and Bihar fell between 1981 and 2020.
Kolkata: Gangetic Bengal and parts of northeast India have shifted out of the tropical savannah climate zone into a temperate zone over seven decades, according to a new study by scientists from the India Meteorological Department (IMD) and the Indian Institute of Tropical Meteorology (IITM), Pune. The shift does not mean Bengal is becoming cooler. Rather, it reflects a changing combination of temperature and seasonal rainfall — including rising maximum temperatures. The study also found a worrying rainfall decline. Researchers linked this to the Victoria Mode — a recurring pattern of sea-surface temperature variations in the North Pacific. During its negative phase, atmospheric circulation changes reduce moisture transport towards the Indo-Gangetic plains, suppressing rainfall over Bengal and neighbouring regions.