Impacts of improved horizontal resolutions in the simulations of mean and extreme precipitation using CMIP6 HighResMIP models over West Africa

Abstract

We analyzed 16 historical simulations from High-Resolution Model Intercomparison Project (HighResMIP) within the framework of Coupled Model Intercomparison Project (CMIP) Phase 6 (CMIP6). The simulations comprise high and low-resolution simulations. The aim is to examine the effect of improved horizontal resolution models on mean and extreme precipitation over West Africa from 1985 -2014. Observation shows southeast and southwest regions are the most active in precipitation, consistent with simulations of HighResMIP. The impact of improved horizontal resolutions is felt in the simulation of orographic-induced rainfall over the high grounds and the intensi cation of precipitation in most of the metrics employed. The observed highest 1-day precipitation shows most of the Guinea coast region had 1-day rainfall greater than 100 mm, which was over-estimated (under-estimated) by high (low) resolution simulations. Also, improvement in horizontal resolution seems to improve the capacity of highresolution models to reproduce the observed pattern of heavy precipitation (R10mm) days and very heavy rainfall (R20mm) days. The spatio-temporal analysis showed the presence of uncertainty in the simulation of both the high and low resolutions simulations in reproducing the extreme precipitation over West Africa. Due to this, a bias correction approach was employed.Recently, several studies have been done. For instance, Molteni et al. (2020) discovered the HighResMIP simulations' ability to capture the tropical Indo-Paci c rainfall and its modulations. Xin et al. (2021)