Convection-permitting modeling strategies for simulating extreme rainfall events over Southeastern South America

Martín Feijoó,Silvina Solman

doi:10.1007/s00382-022-06226-z

Abstract

A set of six convection-permitting (CP) domain configurations were implemented to perform 72-hour long simulations of three extreme precipitation events over Southeastern South America (SESA). The goal of the study is to determine the most adequate configuration for reproducing not only the rainfall evolution and intensity, but also the synoptic triggering mechanisms that led to these extreme events, taking into account the trade-off between model performance and computational cost. This study assesses the impact of (1) the horizontal resolution in the CP domain, (2) the horizontal resolution of the driver domain, (3) the size of both CP and driver domains and (4) the nesting strategy (one-step versus two-step nesting). Each simulation was performed with the Weather Research and Forecasting model driven by the ERA-Interim reanalysis. For each event and domain configuration, a 6-member physics ensemble is built, making a total of 36 simulations for each event. No significant differences were found between the 4 km and 2.4 km CP ensembles. Increasing the horizontal resolution of the driver domain from 20 km to 12 km introduced only subtle differences. Increasing the size of the CP domain improved the model performance, probably because of better resolved topography and, hence, better resolved synoptic environment. The results in this study reveal that the one-step nesting CP ensemble at 4 km horizontal resolution covering an area of \(29^\circ\)x \(21^\circ\) (lon-lat) arises as the optimal domain configuration among these tested to simulate extreme precipitation events over SESA.

Highlights

Southeastern South America (SESA) hosts some of the most extreme convective storms of the planet (Zipser et al, 2006), accounting for more than 70% of the total extended summer precipitation in the region (Rasmussen et al, 2016)
The results in this study reveal that the one-step nesting CP ensemble at 4 km horizontal resolution covering an area of 21◦ x29◦ arises as the optimal domain configuration to simulate extreme precipitation events over SESA
The frequency and intensity of these events are expected to continue increasing in response to the future global warming, as revealed in several studies based on either global climate models (GCMs) or regional climate models (RCMs) (Chou et al, 2014; Blazquez and Though several studies have demonstrated the added value of RCMs in reproducing regional scale phenomena and precipitation-related features over several areas of the world (Torma et al 2015 for Europe; Falco et al 2019 and Solman and Blazquez 2019 for South America, among others), RCMs are still deficient in reproducing extreme precipitation features mostly related with the limitations of the convective schemes (Prein et al, 2015)

Summary

Introduction

Southeastern South America (SESA) hosts some of the most extreme convective storms of the planet (Zipser et al, 2006), accounting for more than 70% of the total extended summer precipitation in the region (Rasmussen et al, 2016). This certainly makes extreme precipitation events of critical relevance, because of the high vulnerability of the population and the socio-economic activities (Vörösmarty et al, 2013), and given that extreme precipitation has been increasing in frequency and intensity during the last decades (Penalba and Robledo, 2010; Cerón et al, 2020; Olmo et al, 2020). There is an urgent need for implementing new modelling strategies to improve the capability of reproducing one of the most important climatic features in the region

Objectives

Results

Conclusion