Climate model simulation and projections of precipitation changes over West Africa

Abstract

Changes in precipitation characteristics have been identified to exert profound socio-economic consequences over West Africa. This study analysed climate model simulation and projections of precipitation changes over West Africa using the Norwegian Earth System Model (NorESM with Lat-Lon resolution of 1.89° by 2.5°). The skill of the model in reproducing the observed precipitation was evaluated for the present-day (1980-2005), its bias and relationship was determined using satellite derived precipitation data from Global Precipitation Climatology Project (GPCP). Using three possible future levels of atmospheric greenhouse gases concentration referred to as Representative Concentration Pathways (RCP) 2.6, 4.5 and 8.5, we calculated projected changes in mean precipitation for the early (2010-2035), mid (2040-2065) and late (2070-2095) twenty first century relative to the present-day period. The result of the analysis shows that precipitation decreases from the Guinea coast to the Sahel. The model also reproduced the general precipitation pattern with maximum and minimum precipitation of ~2600 mm and ~50 mm respectively. However, there are notable biases in southern Cameroun where precipitation is overestimated up to 90 mm and the Guinea-Sierra Leone coast where about 90 mm is underestimated. Despite this, there is a significant positive correlation between NorESMsimulation simulation and GPCP-observed precipitation over the entire West Africa, Guinea Coast and the Sahel region at 0.98, 0.96 and 0.87 respectively. The projected changes in precipitation show that annual precipitation amount will increase over the Guinea coast and decreases further inland. Precipitation will intensify during June-July-August and September-October-November seasons in all RCPs. RCPs 8.5 and 4.5 projects intensification of precipitation over the Guinea coast and a slight increase over the Sahel. Late and mid twenty first century is projected to be wetter than the early and present day period. These patterns will likely cause flooding along shallow drainage basins and the coast especially in the mid twenty first century over the coast of Nigeria and Cameroun and most parts of West Africa. It will also lead to shift in the ecosystem which will affect agriculture and possibly change the distribution of disease vectors, cause water pollution and scarcity which will adversely affect the livelihood of the people in the region. Because of the importance of this projected pattern of precipitation changes, it is recommended that further studies be carried out to quantify the possible future impacts of precipitation changes over strategic sectors as well as posit mitigation and adaptation measures for the wellbeing of the people.