Atmospheric circulation to constrain subtropical precipitation projections

Abstract Accurately assessing future changes in precipitation presents one of the greatest challenges of climate change. A leading source of uncertainty in precipitation predictions stems from potential future changes in atmospheric circulation. Specifically, 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, we have low confi-dence in the magnitude of such weakening and its impact on regional precipitation patterns. Here, using emergent constraint analyses and observation-based Hadley circulation strength changes, we show that the Hadley circulation is expected to undergo substantially stronger weakening in the coming decades, relative to current predictions. The more pronounced pro-jected weakening of the flow is found to yield a considerable increase in regional subtropical precipitation compared to current forecasts, specifically over Asia, Africa, and the Pacific Ocean. Our findings not only provide more accurate tropical circulation and precipitation projections but also have significant societal impacts, given the scarcity of water in subtropi-cal regions.