19 Mainstreaming Climate Change into Transboundary …
439
The Orange River Catchment within the Orange-Senqu River Basin is generally
arid, with very low annual precipitation and high evaporation rate. Seasonal rainfall
is reported (Knoesen 2012) to be concentrated over only a few months, with approximately 85% of the rainfall in Lesotho occurring during the period from October to
April; as much as 15% of Mean Annual Precipitation (MAP) may occur in a 24-hour
period in some areas.
The complex geology of the basin consists mostly of sedimentary rock of the
Karoo Supergroup with some dolerite intrusions, dolomite, and Kalahari sands.
Groundwater is the main source of supply, particularly in the western parts of the
basin. A high erosivity index and poor land management practices (such as overgrazing, cultivation of steep slopes, uncontrolled burning, and alluvial diamond
mining) have led to high erosion rates and sediment loading (Knoesen 2012). Agriculture is typically a major water consumer at more than 60% of total use. Water is
often transferred from plentiful to water-deficient areas. High variability in climate,
low rainfall, a high evaporation rate, and non-climatic stress factors such as deterioration in water quality, increasing competition for water use, and challenges associated
with access all render the basin vulnerable.
3.2 Modeling Climate Change Impacts
Most of the projected climate change-related work in the Orange-Senqu River Basin
is based on research by Knoesen et al. 2009, Knoesen 2012) and Schulze (2011).
The agro-hydrological ACRU model (a daily time step physical conceptual model)
was used (Fig. 5) at the University of Kwa-Zulu Natal to predict climate change
impacts on hydrology and water resources.
Earlier, (i.e., prior to delineation of catchments into the current finer scale) the
South African Department of Water and Sanitation had delineated South Africa,
including both Lesotho and Swaziland into 1946 interlinked and hydrologically
cascading Quaternary Catchments (Schulze 2011), that was deemed too coarse to
represent climatologically homogeneous units and thus that could not appropriately
depict hydrological responses to climate impacts (Fig. 6).
The southern Africa area modeled using ACRU also covers much of the OrangeSenqu River Basin. The entire area is now sub-delineated into quinaries (i.e., at higher
resolution) that resulted in 5 838 hydrologically interlinked and cascading quinaries
covering the RSA, Lesotho, and Swaziland.
439
The Orange River Catchment within the Orange-Senqu River Basin is generally
arid, with very low annual precipitation and high evaporation rate. Seasonal rainfall
is reported (Knoesen 2012) to be concentrated over only a few months, with approximately 85% of the rainfall in Lesotho occurring during the period from October to
April; as much as 15% of Mean Annual Precipitation (MAP) may occur in a 24-hour
period in some areas.
The complex geology of the basin consists mostly of sedimentary rock of the
Karoo Supergroup with some dolerite intrusions, dolomite, and Kalahari sands.
Groundwater is the main source of supply, particularly in the western parts of the
basin. A high erosivity index and poor land management practices (such as overgrazing, cultivation of steep slopes, uncontrolled burning, and alluvial diamond
mining) have led to high erosion rates and sediment loading (Knoesen 2012). Agriculture is typically a major water consumer at more than 60% of total use. Water is
often transferred from plentiful to water-deficient areas. High variability in climate,
low rainfall, a high evaporation rate, and non-climatic stress factors such as deterioration in water quality, increasing competition for water use, and challenges associated
with access all render the basin vulnerable.
3.2 Modeling Climate Change Impacts
Most of the projected climate change-related work in the Orange-Senqu River Basin
is based on research by Knoesen et al. 2009, Knoesen 2012) and Schulze (2011).
The agro-hydrological ACRU model (a daily time step physical conceptual model)
was used (Fig. 5) at the University of Kwa-Zulu Natal to predict climate change
impacts on hydrology and water resources.
Earlier, (i.e., prior to delineation of catchments into the current finer scale) the
South African Department of Water and Sanitation had delineated South Africa,
including both Lesotho and Swaziland into 1946 interlinked and hydrologically
cascading Quaternary Catchments (Schulze 2011), that was deemed too coarse to
represent climatologically homogeneous units and thus that could not appropriately
depict hydrological responses to climate impacts (Fig. 6).
The southern Africa area modeled using ACRU also covers much of the OrangeSenqu River Basin. The entire area is now sub-delineated into quinaries (i.e., at higher
resolution) that resulted in 5 838 hydrologically interlinked and cascading quinaries
covering the RSA, Lesotho, and Swaziland.