Nonlinear Response of Extreme Precipitation to Warming in CESM1
Climate models disagree on the rate at which tropical extreme precipitation increases in response to warming. We investigate the extreme precipitation response in a large ensemble of simulations with one model, the Community Earth System Model version 1, the predecessor to DOE’s E3SM model. We examine polynomial fits of ensemble and spatially-averaged extreme precipitation, quantified by the heaviest day of accumulated precipitation each year, against temperature, and their changes in CESM1, E3SM, and CMIP5 models. We also probe the relationships of extreme precipitation to moisture, circulation, different precipitation parameterizations, and aerosol forcing in CESM1.
We show that extreme precipitation is quadratically related to global-mean surface temperature in CESM1. While some models share this nonlinear response, CESM1 has a larger nonlinearity than most; in E3SM any nonlinearity is small. The nonlinearity is associated with circulation change and an increase in large-scale precipitation; it is not associated with increased moisture or aerosol forcing change. Nonlinearities in extreme precipitation mean that methods that assume linearity and additivity of extreme precipitation responses to different climate forcings are not valid approaches for this variable.
Extreme precipitation is a climate impact driver, but climate models disagree on how it responds to global warming. Focusing on the CESM1 Large Ensemble, predecessor to E3SM, we show that the response of extreme precipitation in the tropics to warming is quadratic, rather than linear. This nonlinearity is larger than in most other climate models, including E3SM. It is associated with strengthening circulation and increases in large scale (rather than convective) precipitation. It is not due to increased moisture or changes in aerosol forcing.