Atmospheric circulation to constrain subtropical precipitation projections

Abstract Accurately assessing future precipitation changes is one of the largest challenges of climate change. A leading source of uncertainty in precipitation predictions stems from potential fu10 ture changes in atmospheric circulation1, 2. Specifically, in the tropics, changes in the Hadley circulation are expected to considerably affect precipitation in dry subtropical and wet equatorial regions3–6. However, while climate models project a robust weakening of the Northern Hemisphere circulation in the coming decades1, 7, currently, we have low confidence in the magnitude of such weakening and its impact on regional precipitation patterns1. Here, using emergent constraint analyses and observed-based Hadley circulation strength changes8, we show that the Hadley circulation is expected to undergo substantially stronger weakening in the coming decades, relative to current predictions. The more robust projected weakening of the flow is found to yield more than a doubling of subtropical precipitation increase than currently forecasted, while it implies a weaker future increase in equatorial precipitation. Our findings not only diminish the uncertainty surrounding tropical circulation and precipitation projections but also suggest that the dry Northern Hemisphere subtropics, currently projected to get drier, might, in fact, get wetter in the coming decades.