The future extreme precipitation systems of orographically locked diurnal convection: the benefits of using large-eddy simulation ensembles

Abstract

The precipitation hotspot of the orographically locked convection highly depends on the interactions among physical processes governing local energetics and cloud dynamics. Accurately estimating the future change of these hotspots will require a model with sufficient spatial resolution as well as an appropriate representation of the critical physical processes. In this study, ensembles of TaiwanVVM large-eddy simulations (Δx=500 m) were designed to capture the summertime diurnal convection in Taiwan when local circulation dominates. The precipitation hotspots identified by long-term observations are well represented by the present-day ensemble simulations with appropriate environment variabilities. A pseudo global warming experiment is carried out to identify changes in convective structures, which results in local rainfall changes. Under the scenario of 3-K uniform warming with conserved relative humidity, the changes in the thermodynamic environment feature an overall higher convective available potential energy (CAPE) and a small decrease in convective inhibition (CIN), owing to the marked increase in low-level water vapor in the marine boundary layer. The results show that mean precipitation and the occurrence of extreme convective systems (ECSs) increase, with hotspots over mountains expanding toward the foothills and plains. The response in cloud dynamics leads to more short-duration, intense rainfall events. The tracking of extreme convective systems with maximum rainfall exceeding 100 mm hr-1 reveals more numerous short-lived ECSs (lifetime < 6 hr) and the enhancements in maximum updrafts by ~10 m s-1, in cloud top heights by ~1 km, and in the volume of cloud objects by ~1.5 folds. These sets of high-resolution simulations under the specific weather regime offer critical information for assessing the potential impacts of the future changes of extreme rainfall contributed by the orographically locked diurnal convection on natural disasters and water resources.