Tropical precipitation response to anthropogenic climate change in recent decades.

Abstract

Tropical rainfall plays a central role in the climate system, shaping ecosystems and societies. Here we show that recent tropical rainfall changes are primarily driven by spatial shifts in atmospheric circulation rather than thermodynamic processes, and cannot be explained by the "Wet Get Wetter" or "Warm Get Wetter" paradigms. Observations reveal a northward shift in precipitation with wetting in the western and northern equatorial Pacific, northern Indian region, and drying south of the equator in the Pacific and South America. These trends coincide with a La Niña-like sea surface temperature pattern, strengthened Walker circulation, Southern Ocean cooling, enhanced land-sea and inter-hemispheric thermal gradients, and intensification of the Indo-Pacific warm pool. Climate models largely miss the first three features, projecting instead a reduced equatorial Pacific sea surface temperature gradient, but capture large-scale thermal gradients and Indo-Pacific warm pool changes. We show that amplified land-sea thermal contrast and Indo-Pacific warm pool intensification reproduce the observed circulation and rainfall changes. Coupled sensitivity experiments further confirm that land warming and ongoing desertification in the Northern Hemisphere act as active drivers of current tropical hydroclimate changes, challenging ocean-centric assumptions in current climate models.