Increases in extreme precipitation over the northeast US using 25-km GFDL SPEAR

Simulating regional extreme precipitation remains challenging, partially limited by climate models’ horizontal resolution. Our recent work, using the climate model ensembles generated by GFDL (Geophysical Fluid Dynamics Laboratory) SPEAR (Seamless System for Prediction and EArth System Research) models, shows that a model with 25 km atmospheric horizontal resolution facilitates a much more realistic simulation of extreme precipitation than comparable models with 50 or 100 km resolution. We take the Northeast United States as an example as the Northeast US has faced the most rapidly increasing occurrences of extreme precipitation within the US in the past few decades. The 25-km GFDL-SPEAR ensemble simulates the trend of Northeast US extreme precipitation quantitatively consistent with observed trend over recent decades. We therefore use the same model for assessments of meteorological factors, including atmospheric rivers (AR) and tropical cyclone (TC)-related events, that have contributed to the trend of extreme precipitation over the Northeast US and future projections. This presentation will show that the increasing extreme precipitation over the Northeast US since the 1990s were mainly linked to TC-related events, especially extratropical transitions. In the future warming climate, both AR-related and TC-related extreme precipitation over the Northeast US are projected to increase, even though the numbers of TC in the North Atlantic are projected to decrease in the 25-km GFDL-SPEAR SSP5-8.5 simulations. On the other hand, the increase in AR-related extreme precipitation is projected to outpace the increase in TC-related extreme precipitation. Given the distinct spatial patterns of extreme precipitation resulting from these two phenomena, changes in their relative contributions could have profound implications for flood prevention and mitigation strategies.