Reversal of extreme precipitation trends over the Northeast US in response to aggressive climate mitigation

Rapid reductions in greenhouse gas (GHG) concentrations are increasingly included in scenarios used to project the full range of possible future climate change, yet the response of regional climate extremes to such reductions remains highly uncertain. Here we focus on projected changes in extreme precipitation over the Northeast United States (US) in response to rapid reductions in GHG concentrations later this century. The Northeast US, the most densely populated region in North America including the Boston to Washington, D.C. metro corridor, has faced the most rapid increase in extreme precipitation events within the US over recent decades. With millions of people and critical infrastructure at risk, understanding how extreme precipitation may respond under different mitigation pathways is essential for informing urban adaptation and resilience strategies.

We use an ensemble of simulations driven by the SSP5-3.4OS scenario from the fully-coupled 25-km GFDL (Geophysical Fluid Dynamics Laboratory) SPEAR (Seamless system for Prediction and EArth system Research) model. In this overshoot scenario, hypothetical mitigation efforts are introduced starting in 2041, with net-negative GHG emissions achieved by the late 21^st century. The frequency of extreme precipitation over the Northeast US increases through mid-century under rising radiative forcing but begins to decline following the sharp reductions in GHG concentrations. However, the timing of this reversal exhibits pronounced seasonality. In the warm season (May – November), extreme precipitation frequency begins to decline shortly after GHG drawdown begins. In the cold season (December – April), on the other hand, the frequency continues rising for roughly a decade after the peak global mean warming and exhibits hysteresis behavior. This delayed response in the cold season is spatially heterogeneous, suggesting that major metropolitan areas in the Northeast may experience different seasonal changes under the same climate migration efforts. These results highlight the benefit of climate mitigation in reducing extreme precipitation events, but also the complexity of regional climate responses, which can be modulated by seasonality, local-scale effects, and other factors.