Scaling of Extreme Precipitation with Temperature as an Emergent Constraint for ESM-Projected Future Changes

Earth system models project a wide range of changes of extreme precipitation intensity (EPI) with warming. This range of uncertainty may be reduced by constraining the rate of EPI with an "emergent constraint", an observable metric that is highly correlated with projected rate of changes in Earth System Models (ESMs). Here we propose that the rate of weather-scale EPI scaling with temperature (EPI-T) in saturated atmosphere can serve as an emergent constraint for future projected EPI changes. In this study we assess the suitability or potential of the EPI-T scaling rate as an emergent constraint based on output from regional and global earth system models. Specifically, for analyses on historical climate and changes, we use output from four-decade simulations of the Weather Research and Forecasting (WRF) model over the CONUS at two different spatial resolutions (one at 4km and one at 12km resolution) driven with boundary conditions from the ERA5 reanalysis data; for analyses on future climate changes, we use output from multiple CMIP6 ESMs. Observational data suggests that the EPI-T scaling roughly follows the Clausius-Clapeyron (CC) scaling rate of approximately ~7% per degree of temperature increase in saturated atmosphere; the model-produced EPI-T scaling rates range from sub-CC to significantly super-CC, and appears to be a robust model signature that changes little with warming. Moreover, preliminary results demonstrate a significant correlation between the weather-scale EPI-T scaling rate and the rate of EPI changes with warming at the climate timescale. These together provide strong evidences for the potential role of the EPI-T scaling as an emergent constraint for future EPI changes. Follow-up research will examine how applying this emergent constraint may revise the range of uncertainty in ESM-projected rates of EPI changes.