ghana climate change vulnerability and adaptation assessment

Water balance models indicate for the Basin as a whole that small changes in rainfall totals (negative orpositive) can produce large changes inrunoff totals (negative or positive) (Andreini et al., 2000; Lemoallee andCondappa, 2009). For example, meanrunoff between 1936-19611 (pre-Akosombo dam closure) and 1965-1998 decreased between8-14 percentin response to a small, 5 percent decrease in Basin rainfall. The modelsalso indicate that only about 9 percent of the rain falling in the basin appears in Lake Voltaas runoff. Otherevaluations indicate a 10percent change in annual rainfall produces a 39 percent change in river inflow intothe Lake Volta (Figure 10.3; Lemoallee and Condappa, 2009). Hence, shifts in land use, water storage or use,or climate vagaries that have relativelysmall impacts on water flux through the upland areas (e.g., a change inevapotranspiration of a few percent) can result in large changes in percentage of runoff reaching the lake.Again, thisalso emphasizes the potential risk to hydropower production with increases in temperatures (andevaporation) and decreased or highlyvariable rainfall induced byy climate change.Source: Lemoalle and Condappa, 2009Figure 10.3 Observed inflows to Lake Volta as a function of rainfall, 1985-1999Water flowing through the Akosombo Dam increased from 28 km³/yr to 35 km³/yr in the1990s, an increaseof 25 percent (Andreinii et al., 2000). As demand for electricity increases, the temptation to generate power athigher rates may trump concerns over drought or storage deficits. Because off drought deficits in the 1980sand continued power generation, Lake Volta levelsnever recovered to optimal operating conditions in the1990s (van de Geisen et al., 2001; Kasei, 2009, Figure 10.4). Thee mean volume stored in the reservoir inthe1970s was132 km³ but in the 1980s and 1990s themean volumee was 102 km³, a reduction of 20 percent(Andreini et al., 2000).The response of Lake Volta to relatively small changes in runofff is also demonstrated in hydrologicalmodeling. Hydrologicall model runs (WEAP software) were aimed at assessingeffects of climate change andupstream reservoir storage on water levels and power generatingg capabilities in Lake Volta (de Condappaa etal., 2008, 2009; Lemoalle and Condappa, 2009). Twenty-year scenarios (with 2000 as the initial condition)were simulated under wetter (meteorological CRU grids shifted 1° north) andwarmer (2° C increase)conditions, drier (grids shifted 1° south) and warmer conditions, warmer conditions, and reference condition(no change from 1980-2000 conditions) (Figure 10.4). The scenario of increased temperature affected LakeVolta by slightly reducing the water level, but the scenarios withh changed rainfall had a much more dramatic168 GHANA CLIMATE CHANGE VULNERABILITY AND ADAPTATION ASSESSMENT