15 Impacts of Climate Change on Water Resources …
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anomalies of temperatures from the mean of the reference period show that the basin
was cooler than the average temperature before the 1980s. This was confirmed by
multi-model ensembles of CORDEX RCMs and observations from Climate Research
Unit (Harris et al. 2014). Also, in recent decades, warming has grown at a sharp and
unprecedented rate, and is projected to increase. Warming estimates based on the two
scenarios diverge in the 2040s, with RCP8.5 warming at higher rate than RCP4.5.
RCP4.5 is projected to have temperature anomalies in the range of 1.5 to 4 °C and
RCP8.5 in the range of 4 to 6 °C by 2100. Overall, the basin is likely to increase in
temperature from 1.5 to 6 °C by 2100 (Sylla et al. 2016). These findings confirm the
projection for increased temperatures in the 3rd National Communication of Ghana
(UNFCCC 2015b) and 2nd National Communication of Burkina Faso (UNFCCC
2015a) submitted to the UNFCCC. Temperatures in Ghana are projected to increase
between 1 and 7 °C by 2080 in all the agro-ecological zones and in Burkina Faso by
0.9 °C by 2025 and 1.5 °C by 2050 in the whole country. In addition to the different
time horizons of these projections, the extent of increase in the temperatures also
vary among the studies. Standardization and harmonization of studies in the basin
and West Africa sub-region, in general, will be necessary.
Relating to precipitation, Sylla et al. (2016) showed great inter-annual variability
in the basin, with rainfall measured between −0.5 and 0.5 mm/decade, making detection of negative or positive trends in rainfall very difficult. However, positive anomalies dominated, even with some negative anomalies projected. This suggests that the
occurrence of wetter conditions is highly probable in the basin in the future. Mean
annual rainfall in the Guinea Savannah of Ghana (in the Volta Basin) is projected
to decrease by 3.5% in 2021–2040, 0.9% in 2041–2060 and 3.1% in 2061–2080.
However, for the Sudan Savannah, the mean annual rainfall is projected to decrease
by 3.2% by 2021–2040, increase by 0.8% in 2041–2060 and decrease by 2.3% by
2061–1080. The results also show no clear trend in the decadal analysis. Available
projection of rainfall in Burkina Faso’s 2nd National Communication (UNFCCC
2015a) did not use GCM-RCM modeling. Moreover, the study was for the whole
country and did not focus on agro-ecological zones. The results of that study indicate
that rainfall could decrease by 6.4% by 2025 and by 11% by 2050 in the worst-case
scenario. This result does not support evidence of a negative or downward trend in
projected rainfall.
The variability of inter-annual rainfall magnitudes bears on the availability of
water for socioeconomic development. Variability can impact on surface and groundwater resources needed to supply water for domestic, industrial and irrigation use,
hydro-power generation and hydro-ecology for the sustenance of flora and fauna.
Inadequate rainfall in the basin as experienced in 1970 and 1983–1984 can have
a significant negative impact on rain-fed agriculture, a major economic activity in
the basin. While inter-annual rainfall variability is important, rainfall distribution
– onset, duration and intensity – and its variability within each year is also of great
importance to agricultural productivity. These studies have examined the impacts
of climate change on the variability of rainfall distribution, and have shown that
the onset of the rainy season has been shifting forward from April to May (van de
Giesen et al. 2010 and Laux et al. 2007). Knowing when the rainy season will begin
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anomalies of temperatures from the mean of the reference period show that the basin
was cooler than the average temperature before the 1980s. This was confirmed by
multi-model ensembles of CORDEX RCMs and observations from Climate Research
Unit (Harris et al. 2014). Also, in recent decades, warming has grown at a sharp and
unprecedented rate, and is projected to increase. Warming estimates based on the two
scenarios diverge in the 2040s, with RCP8.5 warming at higher rate than RCP4.5.
RCP4.5 is projected to have temperature anomalies in the range of 1.5 to 4 °C and
RCP8.5 in the range of 4 to 6 °C by 2100. Overall, the basin is likely to increase in
temperature from 1.5 to 6 °C by 2100 (Sylla et al. 2016). These findings confirm the
projection for increased temperatures in the 3rd National Communication of Ghana
(UNFCCC 2015b) and 2nd National Communication of Burkina Faso (UNFCCC
2015a) submitted to the UNFCCC. Temperatures in Ghana are projected to increase
between 1 and 7 °C by 2080 in all the agro-ecological zones and in Burkina Faso by
0.9 °C by 2025 and 1.5 °C by 2050 in the whole country. In addition to the different
time horizons of these projections, the extent of increase in the temperatures also
vary among the studies. Standardization and harmonization of studies in the basin
and West Africa sub-region, in general, will be necessary.
Relating to precipitation, Sylla et al. (2016) showed great inter-annual variability
in the basin, with rainfall measured between −0.5 and 0.5 mm/decade, making detection of negative or positive trends in rainfall very difficult. However, positive anomalies dominated, even with some negative anomalies projected. This suggests that the
occurrence of wetter conditions is highly probable in the basin in the future. Mean
annual rainfall in the Guinea Savannah of Ghana (in the Volta Basin) is projected
to decrease by 3.5% in 2021–2040, 0.9% in 2041–2060 and 3.1% in 2061–2080.
However, for the Sudan Savannah, the mean annual rainfall is projected to decrease
by 3.2% by 2021–2040, increase by 0.8% in 2041–2060 and decrease by 2.3% by
2061–1080. The results also show no clear trend in the decadal analysis. Available
projection of rainfall in Burkina Faso’s 2nd National Communication (UNFCCC
2015a) did not use GCM-RCM modeling. Moreover, the study was for the whole
country and did not focus on agro-ecological zones. The results of that study indicate
that rainfall could decrease by 6.4% by 2025 and by 11% by 2050 in the worst-case
scenario. This result does not support evidence of a negative or downward trend in
projected rainfall.
The variability of inter-annual rainfall magnitudes bears on the availability of
water for socioeconomic development. Variability can impact on surface and groundwater resources needed to supply water for domestic, industrial and irrigation use,
hydro-power generation and hydro-ecology for the sustenance of flora and fauna.
Inadequate rainfall in the basin as experienced in 1970 and 1983–1984 can have
a significant negative impact on rain-fed agriculture, a major economic activity in
the basin. While inter-annual rainfall variability is important, rainfall distribution
– onset, duration and intensity – and its variability within each year is also of great
importance to agricultural productivity. These studies have examined the impacts
of climate change on the variability of rainfall distribution, and have shown that
the onset of the rainy season has been shifting forward from April to May (van de
Giesen et al. 2010 and Laux et al. 2007). Knowing when the rainy season will begin