Impact of Cumulus Parameterization Schemes with Multigrid Nesting on the High-Resolution Simulation of an Extreme Heavy Rainfall Event in Chongming, Shanghai

This study utilized the observational precipitation data from 1980 to 2017 to analyze the characteristics of annual precipitation and heavy rainfall days at the Chongming station. One extreme heavy rainfall event in 2015 was completely examined using the Weather Research and Forecasting model (version 3.9.1.1) focusing on the impacts of different cumulus parameterization schemes (two traditional schemes, KF and BMJ, and a scale-aware GF scheme) and multigrid nesting configurations. Various statistical methods were adopted to verify the model simulations against the observations. Results showed that using double nesting with a high ratio (9:1 or 15:1) can more realistically produce extreme rainfall distributions and hourly variations compared with the traditional small ratio (3:1 or 5:1) triple nesting grids that produced a lower threat score (TS) for extreme rainfall and underestimated the primary rainfall peaks. On the other hand, the KF and BMJ schemes in the outer grids showed advantages over the GF scheme for the inner 1-km and 3-km simulations of extreme rainfall distribution and hourly rainfall variations. The GF scheme tended to underestimate the extreme rainfall amount over the eastern estuary and TS scores for heavy and extremely heavy rain intensity.