Simulating the Impact of Agri-Silviculture on the Future Climate of West Africa

Abstract

The study investigated the influence of agri-silviculture on the projected future climate in West Africa using regional climate model (RegCM4). The performance of the model in the representation of surface processes over West Africa was evaluated and validated. Thereafter, the future climate change over West Africa was projected using the validated model. Investigation of the influence of different percentages cover of trees/shrubs and crops on the future climate of West Africa was also examined. Eleven numerical agri-silviculture experiments with time-invariant vegetation and dynamic vegetation were used to simulate the historical and future climates of West Africa. The first three experiments simulated the historical climate of West Africa from 1979-2004 using timeinvariant vegetation (PRES), dynamic vegetation in a smaller Africa domain (PRESd1) and dynamic vegetation in a larger Africa domain (PRESd2). The next three experiments projected the future climate from 2029-2054 with time-invariant vegetation (FUTU), dynamic vegetation in a smaller Africa domain (FUTUd1), dynamic vegetation in a larger Africa domain (FUTUd2). The next experiments were carried out using different percentages cover of trees/shrubs and crops along Guinea Savanna zone using time-invariant vegetation (GUSAG), dynamic vegetation in a smaller Africa domain (GUSAGd1) and larger Africa domain (GUSAGd2) in order to represent agri-silviculture. The last two agri-silviculture experiments were carried out along the West Africa coast using time-invariant vegetation (COAG) and dynamic vegetation (COAGd1). All future climate experiments were carried out under Representative Concentration Pathways 4.5 Scenario (RCP4.5). Model performance was evaluated by comparing historical climate simulations with gridded Climate Research Unit (CRU) datasets and Era-Interim reanalysis atmospheric data products. Generally, the historical simulation reproduces the seasonal evolution of precipitation and temperature regimes very well with correlations greater than 0.8 but with a cold and wet bias of 1 -2°C and 1 mm/day respectively. However, a narrow monsoon flow and weaker Jets were simulated in August. Widespread warming is projected in the near future across most parts of West Africa which range from an increase of 0.5°C along the coastal and orographic regions from June to August with an increase of more than 1.5°C over the continent in other seasons. Other parts of West Africa were projected to have positive/negative changes in precipitation not exceeding 1 mm/day during the monsoon and post monsoon seasons. The impact of the different simulated agri-silviculture experiments on the future climate of West Africa varied. The GUSAG experiment induces cooling of about 0.5 - 2°C over most areas along the agrisilviculture zone (Nigeria, Ghana, Cote d’Ivoire and Cameroon, Togo, Benin Republic and Ghana) in all seasons. However, the induced cooling does not necessarily translate to more precipitation, except over Ghana where precipitation increases by 0.5 - 1.8 mm/day during MAM and JJA seasons. On the other hand, GUSAG experiment enhances the warming over Liberia and Sierra Leone by about 2°C in all seasons, which intensifies the drying condition to about 1.8 mm/day. The GUSAGd2 experiment induces cooling of about 2°C in areas within 8°E and 16°E along the agri-silviculture zone in all seasons but increases the warming by more than 0.5°C outside this area. Generally, agri-silviculture practice along the coast (COAG and COAGd1) does not necessarily have a large-scale impact on temperature and precipitation over the entire West Africa region. The study concluded that agri-silviculture could be used to mitigate the projected future warming and drying across most West African countries except Liberia and Sierra Leone. Therefore, it is recommended that agri-silviculture practice should be adopted as a land-based strategy to combat food insecurity, deforestation due to agricultural expansion and ameliorate the impacts of climate change in West Africa.