Impacts of Improved Horizontal Resolutions in the Simulations of Mean and Extreme Precipitation using CMIP6 HighResMIP Models over West Africa

Abstract

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 intensification 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 high-resolution 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.