A sensitivity study of the Weather Research and Forecasting model to different physics schemes in convection-permitting mode over Southern Spain

Heavy precipitation events (HPEs) frequently occur in Andalusia (south of Spain), causing major economic losses and affecting human stability. Variations in the precipitation patterns are expected under a changing climate. Hence, a correct characterization and prediction is crucial to better understand this kind of events.

In this region, HPEs are frequently related to deep convection; convection-permitting models (CPMs) can generate more reliable information on small scales due to their high spatial resolution of ≤ 4 km. At this scale, deep convection can be explicitly resolved. Therefore, precipitation features (e.g., patters of diurnal cycle) could be better represented.

In this framework, this study aims to assess the Weather Research and Forecasting (WRF) model version 4.3.3 in convection-permitting mode, analyzing its sensitivity to different parameterization schemes. For this purpose, WRF has been configured using two one-way nested domains: a coarser domain (d01) covering the Iberian Peninsula (IP) at 5 km of spatial resolution, and a finer domain (d02) centered over the Sierra Nevada (SN) mountain range with 1 km spatial resolution. To analyze the model performance under different precipitation conditions, WRF was separately run for two one-year periods, both using as lateral and boundary conditions the ERA5 reanalysis and using one year of spin-up; a wet year, and a dry year. Specifically, the analysis was based on combining two planetary boundary layer options (YSU and ACM2), two microphysics (WSM-6 and Thompson), two radiation (RRTMG and CAM), and two cumulus (Kain-Fritsch and Grell 3D) schemes for the 5-km domain. Additionally, this coarser domain was also tested with the convection scheme switched off.

Sub-daily outputs of precipitation have been compared with different observational products in order to select the best combination of parameterization schemes and to determine whether the model is able to incorporate the effects of topographical features at this spatial resolution. This provides physically consistent results for this region.

Keywords: sensitivity study, convection-permitting climate simulations, Andalusia, heavy precipitation patterns, Weather Research and Forecasting model.

Acknowledgments: This research has been carried out in the framework of the project P20_00035, funded by FEDER/Junta de Andalucía-Consejería de Transformación Económica, Industria, Conocimiento y Universidades, the Spanish Ministry of Science and Innovation (LifeWatch-2019-10-UGR-01), project CGL2017-89836-R, funded by the Spanish Ministry of Economy and Competitiveness with additional FEDER funds, and project B-RNM-336-UGR18, funded by FEDER / Junta de Andalucía - Consejería de Economía y Conocimiento. F. Solano Farías acknowledges the Mexican National Defense Secretary for the predoctoral fellowship.