According to a recent study, a persistent patch of abnormally tropical water in the North Atlantic Ocean may affect where monsoon rains occur in India and where they do not occur - with some areas getting enhanced monsoon rainfall while others are experiencing less.

The researchers' research shows that the North Atlantic cold blob phenomenon has influenced Indian summer monsoons over much of the past two decades. Located south of Greenland, a cooling zone deviates from the recently observed long-term trend of rising sea surface temperatures and may be of interest to many climate scientists.

The research indicates that there have been rising rainfall totals for many areas of northwestern India, including Gujarat, Rajasthan, and parts of northwestern India, while rainfall has decreased across the eastern Indo-Gangetic Plain during the same period. This shift in rainfall has become more prevalent since the start of the 21st century.

According to the researchers, cooler sea surface temperatures in the North Atlantic Ocean affect the way that the Indian summer monsoon rains precipitate, through altering atmospheric circulation patterns that extend from the Atlantic Ocean to Asia. These changes impact the wind systems and moisture transport pathways associated with the Indian summer monsoon.

There is evidence from the study that North Atlantic sea temperatures affect atmospheric conditions that support heavy rainfall in northwest India, while at the same time, changes in those same patterns produce less moisture to be available to eastern and northeastern India, resulting in lower rainfall.

Rainfall variations cannot be explained by local influences alone. Rather, the results imply that ocean conditions thousands of miles away can have a significant impact on monsoon behaviour throughout the Indian subcontinent.

The Indian summer monsoon is 70 per cent of the country’s annual precipitation needs and has been a vital source of support for agriculture, water supply and food production. Variations in the geographic distribution of rainfall will affect the yields of crops, groundwater recharge and the level of reservoirs, especially in regions that rely on seasonal precipitation.

Using observational data and climate model simulations, scientists were able to assess the relationship between North Atlantic ocean temperatures and variability in monsoon patterns. The results point to the North Atlantic cooling pattern as an important contribution to the changing patterns of precipitation from the monsoon system.

The study adds to a growing body of evidence that changes in one area of the global climate system can affect the weather in far-off parts of the world. Understanding these connections could help scientists better predict the long-term progression and develop possibilities for strengthening agricultural and water management in India.