## 2 Materials and Methods  
### Study Area--West Africa  
The area of interest for this literature review is West Africa as defined by the United Nations (UN) in the M49 standard [51], comprising the following countries: Benin, Burkina Faso, Cabo Verde, Cote d'Ivoire, Gambia, Ghana, Guinea, Guinea-Bissau, Liberia, Mali, Mauretania, Niger, Nigeria, Saint Helena, Senegal, Sierra Leone, and Togo. Covering approximately one quarter of Africa, West Africa contains a broad range of ecosystems, bioclimatic regions and habitats from rainforest to desert. From the arid Sahara in the north to the humid southern coast, five distinguishable broad east-west belts characterize the West African climate and vegetation [52] (Figure 1a,b). Figure 1 shows the terrestrial ecoregions delineated based on the biogeographic distribution of species, communities, and endemic genera by [PERSON] et al. [53]. Rainfall levels and temperature also can be used [52; 54] to derive gross biophysiological features resulting in the Saharan, Sahelian, Sudanian, Guinea, and Gunieo-Congolian regions. The Sahara Desert stretches across the whole north extent of West Africa. It is characterized by arid landscapes, dune fields, gravel plains, and rugged mountains. Average annual rainfall ranges from 0 to 150 mm per year. The Sahel is a broad semiarid belt averaging about 350 km wide. Climatically it is characterized by an average rainfall of between 150 and 600 mm, with great variability of amount and timing in a given year, and by a dry season lasting 8 to 9 months (Figure 1). It is also home to countless small wetlands as well as large water features including the Senegal River, the Inland Niger Delta, and the Lake Chad Area. It transitions in the south to the Sudanian Region, which is the domain of savanna, ranging from open tree to wooded savannas and to open woodlands. Annual rainfall is between 600 and 1200 mm and the dry season lasts 5 to 7 months. Further south, the Guinea Region is generally defined by an average annual rainfall of between 1200 and 2200 mm and is the domain of seasonally wet-and-dry deciduous forests. Canopy cover is dense and closed with tree heights averaging 18 to 20 m. It has a distinct dry season of 7 to  
8 months, which distinguishes it from the Guineo-Congolian Region. This is the wettest in West Africa with 2200 to 5000 mm annual rainfall. Here, there are two rainy seasons, one long and a short one interrupted by short, drier periods [52; 53; 55]. The rainfall and temperature patterns are illustrated in Figure 1c, using climate diagrams that present the average temperature and precipitation data from 1991 to 2020. These graphs span from northern to southern regions, showcasing Mauretania and Niger as representative of the Sahel zone, Senegal for the Sudanian region, and Ghana and Sierra Leone as a blend of the Guineo-Congolian zone. Sierra Leone exhibits notably high precipitation amounts characteristic of the Guineo-Congolian zone, while also displaying the distinct dry season of the Guinea region, reflecting national averages. Southern Ghana lacks the extended dry season, instead exhibiting a shorter one, alongside two rainy season peaks. The diversity of bioclimatic zones across West Africa influences the land use and therefore, the types of crops cultivated in the region. Each zone provides distinct environmental conditions that support specific crops, leading to a variety of cropping systems and agricultural outputs essential for both domestic consumption and export. Major staple crops include maize, millet, sorghum, rice as well as groundnut, cassava, and yams [53; 2; 54]. Millet, for instance, is widely grown due to its adaptability to semi-arid conditions, where other crops often require irrigation, and its high nutritional value [55]. Groundnut is a key crop in several countries, including Nigeria, Mali, Cote d'Ivoire, Burkina Faso, Ghana, and Senegal [54].