Atmospheric circulation to constrain subtropical precipitation projections

Accurately assessing future precipitation changes presents one of the greatest challenges of climate change. In the tropics, changes in the Hadley circulation are expected to considerably affect precipitation in dry subtropical and wet equatorial regions. However, while climate models project a robust weakening of the Northern Hemisphere circulation in the coming decades, currently, there is low confidence in the magnitude of such weakening and its impact on regional precipitation patterns. Here we use emergent constraint analyses and observation-based Hadley circulation strength changes to show that the projected circulation weakening will probably be larger than in current predictions. The more pronounced weakening of the flow results in a doubling of the subtropical precipitation increase compared with current forecasts, specifically over Asia, Africa and the Pacific Ocean. Our findings provide more accurate tropical circulation and precipitation projections and have considerable societal impacts, given the scarcity of water in subtropical regions.