Understanding the Scaling of Extreme Precipitation Using a WRF Squall Line Case

Extreme precipitation is usually associated with relatively short-lived precipitating events, which are strongly influenced by the availability of moisture. Therefore, it is tempting to use the Clausius-Clapeyron (CC) relation to scale the response of extreme precipitation to global warming. However, the changes in precipitation extremes may be regionally different and the precipitation increases can be quite different than suggested by the CC scaling. In this study, a WRF squall line idealized case is used to investigate the scaling of extreme precipitation. An ensemble of squall lines in a warmer climate is created by adding the perturbations due to the climate change derived from the simulations using the super-parameterized version of the Community Atmosphere Model (SP-CAM). A larger increase of squall line precipitation than predicted by the CC scaling is found using different microphysics schemes. The squall-line response is split into dynamic and thermodynamic parts using a new scaling parameter. The results show that the changes in squall line precipitation associated with thermodynamic changes are well estimated by the CC scaling for different microphysics used. The super-CC scaling of the squall line precipitation is found to be mostly due to the dynamic changes. The scaling, however, is found to be sensitive to the choice of the microphysics scheme.