The figure above shows the percentage departure of summer monsoon rainfall over central India (76-86°E, 19-26°N) during 1901-2018. Wet years (above 10% departure) are marked in dark blue color and drought years (below -10% departure) are marked in red color. El Niño and La Niña conditions for the summer season are marked using red and blue dots.
Ref: Singh, D., S. Ghosh, M. K. Roxy and S. McDermid, 2019: Indian summer monsoon: Extreme events, historical changes, and role of anthropogenic forcings. WIREs Clim Change. 2019;10:e571, doi:10.1002/wcc.571.
The All-India area-weighted mean summer monsoon rainfall, based on a homogeneous rainfall data set of 306 raingauges in India, developed by the Indian Institute of Tropical Meteorology, is widely considered as a reliable index of summer monsoon activity over the Indian region. Long time series of this index since 1871 have revealed several interesting aspects of the interannual and decadal-scale variations in the monsoon as well as its regional and global teleconnections.