La Niña's Diminishing Fingerprint on the Central Indian Summer Monsoon

TitleLa Niña's Diminishing Fingerprint on the Central Indian Summer Monsoon
Publication TypeJournal Article
Year of Publication2020
AuthorsSamanta D, Rajagopalan B, Karnauskas KB, Zhang L, Goodkin NF
Date Published01/2020

La Niña years tend to provide increased Indian summer monsoon (ISM) rainfall. However, observations show 6‐8% reduction in ISM rainfall during post‐1980 La Niñas relative to pre‐1980. Using a suite of atmospheric general circulation model experiments, we replicate this observed phenomenon and attribute it to a combination of weakening La Niña events themselves plus strongly warming tropical Indian Ocean. We demonstrate that half of the ISM rainfall reduction during post‐1980 La Niñas can be attributed to changes in the spatial pattern and intensity of La Niña within the tropical Pacific Ocean. Warmer eastern‐equatorial Pacific Ocean temperatures during post‐1980 La Niñas weaken the Walker circulation, resulting in large‐scale anomalous subsidence over the Indian subcontinent, thereby, inhibiting the convection that drives ISM rainfall. Further, we demonstrate the declining ISM rainfall during La Niña years with increasing tropical Indian Ocean warming, which has several serious concerns for regional water resources and stability.