Heat and freshwater changes in the Indian Ocean region

Across the Indo-Pacific region, rapid increases in surface temperatures, ocean heat content and concomitant hydrological changes have implications for sea level rise, ocean circulation and regional freshwater availability . In this Review, we synthesise evidence from multiple data sources to elucidate whether the observed heat and freshwater changes in the Indian Ocean represent an intensification of the hydrological cycle, as expected in a warming world. At the basin scale, 20th century warming trends can be unequivocally attributed to human-induced climate change. Changes since 1980, however, appear dominated by multi-decadal variability associated with the Interdecadal Pacific Oscillation, manifested as shifts in the Walker circulation and a corresponding reorganisation of the Indo-Pacific heat and freshwater balance. Such variability, coupled with regional-scale trends, a short observational record and climate model uncertainties, make it difficult to assess whether contemporary changes represent an anthropogenically-forced transformation of the hydrological cycle. Future work must therefore focus on maintaining and expanding observing systems of remotely sensed and in situ observations, as well as extending and integrating coral proxy networks. Furthermore, improved climate model simulations of the Maritime Continent region and its intricate exchange between the Pacific and Indian Ocean are necessary to quantify and attribute Indo-Pacific heat and freshwater changes.