The All India Monsoon Rainfall has been a target of monsoon prediction since the times of Sir Gilbert Walker back in the 1930s. It has a bearing on total food production but is of little value for farmers and water managers at local levels. The dynamic forecast by the India Meteorological Department (IMD)is now targeting rainfall at the district level but the focus remains largely on the impact of El Niño on All India monsoon rainfall. The El Niño – Indian monsoon correlation seems reliable although it has not remained constant, most likely due to global warming.
Now it has emerged that the distribution of rainfall over the Indian subcontinent has large-scale patterns and those patterns are related to global sea surface temperatures or SSTs. A new study published in the journal.
IMD uses six homogeneous regions of rainfall covering all of India which is a statistical construct with no relation to local or remote drivers of the monsoon. The IITB study recasts rainfall into bands of variability around the long-term mean by considering rainfall amounts in 25 Km grids over an entire country divided into near normal, dry, wet, extremely dry and extremely wet years.
This leads to nine clusters of rainfall patterns that are robust and distinct without any a priori assumptions about how they are generated. The patterns depict rainfall deficit over the entire country as in 2002 as well as east-west, north-south and the Western Ghats, patterns of excess and deficit rainfall with many granular details down to district level. These spatial distributions are critical for food, water, and energy production and their interdependence or nexus.