Abstract:
Several studies have noted that West Africa – in particular, the Sahel – experienced the most profound inter-decadal climate variability in the world during the twentieth century (Speth et al., 2011; Obuobie and Ofori, 2013). Similar to overall climate patterns in the region, rainfall in the Volta Basin (Figure 1) is characterised by high spatial and temporal variability which increases as one moves north from the sub-humid zones (van de Giesen et al., 2001; 2010; Brown and Crawford, 2008; Pavelic et al., 2013; UNEP-GEF Volta Project, 2013). Rainfall was unusually high in the 1930s and 1950s, but the region was hit by drought that lasted most of three decades (1970–2000). Rainfall partially recovered for the period 1994–2003 (Opoku-Ankomah and Amisigo, 1998; Friesen and Diekkrüger, 2002; Owusu and Waylen, 2009; McSweeney et al., 2010; Ofori et al., 2015). A 10% decrease in rainfall from the period 1960–2005 resulted in a 200km southward shift of isohyets (UNEP-GEF Volta Project, 2013). The West African Monsoon (WAM; Nikulin et al., 2012; Christensen et al., 2013) is known to influence climate variability over the region, and the WAM itself is influenced by changes in the concentrations of greenhouse gases and aerosols in the atmosphere (Christensen et al., 2013).
