Simulating the impact of varying vegetation on West African monsoon surface fluxes using a regional convection-permitting model.

This study assessed the sensitivity of the West African climate to varying vegetation fractions. The assessment of a such relationship is critical in understanding the interactions between land surface and atmosphere. Two sets of convection-permitting simulations from the UK Met Office Unified Model at 12 km horizontal resolution covering the monsoon period May-September (MJJAS) were used, one with fixed vegetation fraction (MF-V) and the other with time-varying vegetation fraction (MV-V). Vegetation fractions are based on MODIS retrievals between May and September. We focused on three climatic zones over West Africa: Guinea Coast, Sudanian Sahel, and the Sahel while investigating heat fluxes, temperature, and evapotranspiration. Results reveal that latent heat fluxes are the most strongly affected by vegetation fraction over the Sahelian and Sudanian regions while sensible heat fluxes are more impacted over the Guinea Coast and Sudanian Sahel. Also, in MV-V simulation there is an increase in evapotranspiration mainly over the Sahel and some specific areas in Guinea Coast from June to September. Moreover, it is noticed that high near-surface temperature is associated with a weak vegetation fraction, especially during May and June. Finally, varying vegetation seems to improve the simulation of surface energy fluxes and in turn impact on climate parameters. This suggests that climate modelers should prioritize the use of varying vegetation options to improve the representation of the West African climate system.

Implication of stratospheric aerosol geoengineering on compound precipitation and temperature extremes in Africa.

Three Coupled Model Intercomparison Project 5 (CMIP5) models that simulated the G4 experiment of the Geoengineering Model Intercomparison Project (GeoMIP) were used to investigate the impact of stratospheric aerosol injection (SAI) on combined temperature and precipitation extremes in Africa that can have greater negative impacts on human and the environment than individual rainfall or temperature extremes. The examined compound extremes included the dry (Rwarm׀dry and Rcold׀dry) and wet (Rwarm׀wet and Rcold׀wet) modes assessed during the injection (SAI, 2050-2069) and post-injection (postSAI, 2070-2089) periods compared with the historical period (1986-2005). We found a significant projected change in the occurrence of both wet and dry modes during SAI and postSAI related to the historical period. The magnitude and sign of this change depend on the season and the geographical location. During the SAI and postSAI, the wet (Rwarm׀wet and Rcold׀wet) modes are projected to be significantly lower while the dry modes are noted to increase in a large part of African continent depending on the season and the geographical location and may consequently leads to an increase of the droughts prone areas. The termination effect is noted to reduce the occurrence of dry modes, which may reduce the potential negative effects of the injection after halting. As the effect may vary from one region to another and according to the season, it suggested assessing the key sector impacts of SAI. Thus, this change in dry modes due to SAI could affect all activities which depend on water resources such as water supply, agriculture and food production, energy demand, and production with adverse effects on health, security, and sustainable development, but this needs to be assessed and quantified at regional scales.

Potential impact of 1.5, 2 and 3 °C global warming levels on heat and discomfort indices changes over Central Africa.

Investigating the effects of the increased global warming through the lens of the Paris agreements would be of particular importance for Central African countries, which are already experiencing multiple socio-political and socio-economic constraints, but are also subject to severe natural hazards that interact to limit their adaptive capacity and thus increase their vulnerability to the adverse effects of climate change. This study explores changes in heat stress and the proportion of population at risk of discomfort over Central Africa, based on an ensemble-mean of high-resolution regional climate model simulations that cover a 30-year period, under 1.5, 2 and 3 °C Global Warming Levels (GWLs). The heat index was computed according to Rothfusz's equation, while the discomfort index was obtained from Thom's formula. The results show that throughout the year but with a predominance from March to August, the spatial extent of both heat and discomfort categories is projected to gradually increase according to the considered GWLs (nearly threefold for an increasing warming thresholds from 1.5 to 3 °C). As these heat conditions become more frequent, they lead to the emergence of days with potentially dangerous heat-related risks, where almost everyone feels discomfort due to heat stress. It thus appears that the majority of populations living in countries located along the Atlantic coast and in the northern and central part of the study area are likely to be more vulnerable to certain health problems, which could have repercussions on the socio-economic development of the sub-region through decreased workers' productivity and increased cooling degree days. Overall, these heat-related risks are more extended and more frequent when the GWL reaches 2 °C and above.