338
G. A. Manful and Y. Opoku-Ankomah
33 km
3 (8%) and 13 km
3 (3%), respectively; various losses are 1%. Fresh water
availability in the basin is thus very limited, especially in the drier northern part.
2.4 Groundwater
Aquifers in the basin are recharged directly and indirectly. Direct recharge is through
fractured and fault zones as well as through sandy portions of the weathered zones.
Indirect recharge occurs by infiltration through ponds in low-lying areas and also
through riverbeds. Indirect recharge rates are low compared to direct recharge from
rainfall after meeting evapotranspiration demand (HAP 2006; Lemoalle and de
Condappa 2009). Hard rock aquifers, which are low-yielding, underlie about 90%
of the basin.
Groundwater abstraction in the basin is low but with high potential for development. Climate variability and change will have serious impacts on surface waters,
making groundwater use increasingly important. Currently, multiple streams and
springs are drying up as a result of climate change and variability, as well as poor
land use practices (Gyau-Boakye and Tumbulto 2000). Knowledge of aquifer yield
and other characteristics in the basin are limited; more research in this area is needed.
3 Observed Changes in Temperature and Rainfall
Ghana and Burkina Faso make up 85% of the total area of the basin (Lemoalle and de
Condappa 2009); hence temperatures and rainfall in the agro-climatic zones of the
basin used for this study were taken from national statistics of these two countries sent
to the UNFCCC through their national communication reports. The agro-climatic
zone of the Burkina Faso part of the basin is largely Sudano-Sahelian (see Sect. 2.3),
and that of Ghana is Sudanian in the north and Guinean in the midsection of the
country.
3.1 Changes in Historical Temperatures
Over the period 1961–2008, the average annual temperatures in Burkina Faso
increased by at least 0.5 °C at all the synoptic stations (UNFCCC 2015a).
The minimum and maximum temperatures also increased in magnitude. Average
minimum temperatures varied between 20 and 22 °C over 1961–1990 and 1971–
2000, respectively, with the variability of about 2 °C. Maximum temperatures varied
between 0.4 and 3.6 °C, and minimum temperatures for the period 1960–2000 in
Sudan and Guinea Savannah zones in Ghana (in the lower part of the basin) showed
G. A. Manful and Y. Opoku-Ankomah
33 km
3 (8%) and 13 km
3 (3%), respectively; various losses are 1%. Fresh water
availability in the basin is thus very limited, especially in the drier northern part.
2.4 Groundwater
Aquifers in the basin are recharged directly and indirectly. Direct recharge is through
fractured and fault zones as well as through sandy portions of the weathered zones.
Indirect recharge occurs by infiltration through ponds in low-lying areas and also
through riverbeds. Indirect recharge rates are low compared to direct recharge from
rainfall after meeting evapotranspiration demand (HAP 2006; Lemoalle and de
Condappa 2009). Hard rock aquifers, which are low-yielding, underlie about 90%
of the basin.
Groundwater abstraction in the basin is low but with high potential for development. Climate variability and change will have serious impacts on surface waters,
making groundwater use increasingly important. Currently, multiple streams and
springs are drying up as a result of climate change and variability, as well as poor
land use practices (Gyau-Boakye and Tumbulto 2000). Knowledge of aquifer yield
and other characteristics in the basin are limited; more research in this area is needed.
3 Observed Changes in Temperature and Rainfall
Ghana and Burkina Faso make up 85% of the total area of the basin (Lemoalle and de
Condappa 2009); hence temperatures and rainfall in the agro-climatic zones of the
basin used for this study were taken from national statistics of these two countries sent
to the UNFCCC through their national communication reports. The agro-climatic
zone of the Burkina Faso part of the basin is largely Sudano-Sahelian (see Sect. 2.3),
and that of Ghana is Sudanian in the north and Guinean in the midsection of the
country.
3.1 Changes in Historical Temperatures
Over the period 1961–2008, the average annual temperatures in Burkina Faso
increased by at least 0.5 °C at all the synoptic stations (UNFCCC 2015a).
The minimum and maximum temperatures also increased in magnitude. Average
minimum temperatures varied between 20 and 22 °C over 1961–1990 and 1971–
2000, respectively, with the variability of about 2 °C. Maximum temperatures varied
between 0.4 and 3.6 °C, and minimum temperatures for the period 1960–2000 in
Sudan and Guinea Savannah zones in Ghana (in the lower part of the basin) showed