A recent article published in Science Advances analyzed an atmospheric reanalysis dataset (MERRA2) covering the 1980–2016 period to show that a significant warming occurred in the Indian Ocean over the study period, and thus reduced the temperature difference between the Indian subcontinent and Indian Ocean in boreal summer. The reduced land-ocean temperature difference in turn produced anomalous subsidence over the Indian subcontinent, and thus weakened the summer monsoon circulation and wind speeds over India. A series of numerical atmospheric model sensitivity experiments confirmed these findings.
Fig. 4 from Gao et al. (2018): ERRA2–derived spatial distributions of (a) SLP for May-August averaged over the 1980–2016 period and (b) time series of temperature averaged over the Indian subcontinent, EIO, and SIO (regions marked with blue boxes on the left).
Gao, M., Ding, Y., Song, S., Lu, X., Chen, X., & McElroy, M. B. (2018). Secular decrease of wind power potential in India associated with warming in the Indian Ocean. Science Advances, 4(12), eaat5256.