Increasing Freshwater Content off the West Coast of India Since 2013

Abstract

The coastal oceans off India are vital for the exchange of freshwater between the Bay of Bengal and the Arabian Sea. In this region, ocean salinity, as a proxy for ocean freshwater content, significantly impacts upper‐ocean stratification and air‐sea interaction and serves as a vital indicator of the regional hydrological cycle driven by monsoon circulation. Using data sets from multiple satellite missions, in situ observations, and reanalysis products, this study investigates salinity changes off the West Coast of India (WCI) from 1993 to 2023. Remarkably, we have detected a regime shift around 2013, where the trend reversed from increasing salinity to a notable freshening. A mixed‐layer salinity budget analysis reveals that this freshening is driven jointly by oceanic advection and surface freshwater flux, with advection playing a major role. These changes are linked to the recent positive Indian Ocean Dipole (pIOD) events via oceanic and atmospheric processes. pIOD events induce southerly wind anomalies near the WCI, which enhances the northward intrusion of fresh water. Meanwhile, a pIOD operates synergistically with rapid warming in the western equatorial Indian Ocean, intensifying moisture transport toward the WCI and resulting in increased local precipitation. These findings provide new insights into the mechanisms governing coastal salinity changes and their relationship to the regional hydrological cycle under the combined influence of anthropogenic climate warming and natural variability.