The IMD study analysed annual and seasonal rainfall trends in 632 districts and 34 meteorological sub-divisions, barring Ladakh, Andaman & Nicobar and Lakshadweep islands, using rainfall data from 1901 to 2013. Uttar Pradesh finds itself with more than 40% (32 out of 75) of its districts showing a significant drop in rainfall. In Delhi, eight of the nine (old) districts showed the trend.
An IMD scientist involved in the analysis told TOI that while researchers found no trend in countrywide rainfall during the periods studied, subdivision and district-wise trends were apparent. “The aim of the study was to implement suitable measures and ensure proper management of water resources in districts that have shown decreasing rainfall,” the scientist said.
More recent data outside the study, too, reveals a weakening of the monsoon in several parts of north India. The trend is sharpest since 1999. Of the 18 rainy seasons during this period, Haryana received at least 10% below normal monsoon in 13 years. For Punjab, the corresponding figure was 12. Decreasing rainfall has obvious impacts on levels of groundwater, which is increasingly being used in agriculture as well as cities in the region. Satellite studies have revealed alarming levels of over exploitation of groundwater in north India.
The IMD study also revealed an increasing rainfall trend in several districts, including many in Jammu & Kashmir and Bihar, and a few in Jharkhand, Punjab and Chhattisgarh. Scientists involved in the study said it was difficult to pinpoint reasons for the increasing or decreasing trends. An expert at the Indian Institute of Tropical Meteorology reasoned that monsoon circulation had been showing a weakening trend since the 1950s, possibly due to anthropogenic influences like pollution aerosols. “Indo-Gangetic plains are a core monsoon area, where the monsoon trough is located. The weakening of the monsoon circulation may have had its impact on this region too,” he said.