The India Meteorological Department predicted on Monday that the country would experience a normal monsoon for the third successive year, with rainfall at 97% of the long period average (LPA). The monsoon is considered normal if average rainfall is between 96% and 104% of the LPA. Anything less than 90% of the LPA is considered a deficient monsoon.
However, a recent study, conducted by Indian meteorologists, projects that about 50 years from now, the monsoon over the central Indian region is expected to drastically reduce owing to a declining trend observed in the number of Low Pressure Systems (LPS) that usually bring rain to this area.
The region, according to the study, will witness a 45% decline in the frequency of LPS activity, thereby resulting in lesser rainfall in this heavily rain-fed agrarian belt. This downward trend in rainfall is expected to be realised during the decades spanning between 2065-2095, that the researchers have defined as the end of the current century.
The collaborative study, by R S Ajayamohan and a team of scientists from the Indian Institute of Tropical Meteorology (IITM), IIT Delhi, New York University and University of California, which was recently published in PNAS, also highlights a 10% increase in the instances of LPS forming over land, which will eventually lead to extreme rainfall over the North Indian plains.
LPSes originate in the Bay of Bengal, and travel landwards in a southeast-northwest direction crossing Odisha, Andhra Pradesh, Telangana, Chhattisgarh, Jharkhand, Madhya Pradesh, Maharashtra and Uttar Pradesh. This region is known as the core monsoon zone.
Speaking to The Indian Express, Sabin T P, one of the authors and senior scientist from IITM, said, “One of the main reasons for this decrease in rainfall, particularly during the monsoon, could be the largescale decrease in the moist westerly winds travelling from the Arabian Sea, called monsoon circulations, along India’s west coast onto the mainland. In addition, these winds have been observed to have shifted northwards from their normal track during their forward propagation.”
On the importance of studying the core monsoon zone, Ravi Nanjundiah, director of IITM, said, “In order to have a better understanding about the monsoon, this is a very crucial region as most LPS pass by this region during the monsoon season, that is from June to September. A new test-bed facility by the institution is being set up on the outskirts of Bhopal, in order to study these key rain-bearing systems.”
According to R S Ajayamohan, global warming is getting more pronounced with each passing year, when all previously known record temperatures have been surpassed. Additionally, its effect even on the monsoon, especially over this zone, is seen as inevitable.
He said, “With the rise in global temperature, the atmosphere would have a much higher moisture holding capacity. But, at a certain juncture, this capacity would collapse leading to extreme rainfall events, which are anyway found to be increasing in recent years.”