19 Mainstreaming Climate Change into Transboundary …
445
Fig. 11 Percentage change in streamflow between the present (1975–2006) and future (2016–2045).
The map (left) depicts spatial percentage change while the graph (left) depicts the same changes in
streamflow between present and future by also showing the number of quaternary catchments and
corresponding percentage change in streamflow (Department of Water and Sanitation 2019)
ratio changes of 1.1 to 1.5) over the eastern two-thirds of the country, and 50–100%
in the western one-third. The exception is the extreme southwest, where a decrease in
design streamflows is projected when the daily output from multiple GCMs is used
in the ACRU model with techniques to analyze extreme values (Schulze 2011). The
following issues were highlighted in the study:
• As the return period increases from two through five and 10 to 20 years, the
rate of increase in design streamflows decreases and becomes less pronounced,
irrespective of duration (i.e., irrespective of duration of 1 or 7 days).
• The regions within South Africa where the greatest increases in design stormflows
are projected are the transitional areas between summer and winter rainfall regions
where inconsistent weather patterns are likely to be experienced in future.
• On a local scale, as the return period increases from 2 to 20 years, the area in the
southwest expands where decreases in design streamflows are projected.
• For a given return period, the spatial patterns of change into the intermediate
future do not vary among the 1-, 2-, 3-, and 7-day durations, i.e., the changes in
design streamflow appear to be sensitive to return period, but not to duration.
The mean annual streamflow is likely to increase for both the intermediate future
and more distant future since projections indicate higher rainfall events, particularly in the high altitude eastern parts of the basin. Projected increase in mean
annual streamflow is likely to be significantly larger than those projected for mean
annual precipitation because both increases and decreases in rainfall are amplified.
According to Knoesen et al (2009), studies show that variability in streamflow is
projected to increase more in the distant future than the intermediate future. Such
445
Fig. 11 Percentage change in streamflow between the present (1975–2006) and future (2016–2045).
The map (left) depicts spatial percentage change while the graph (left) depicts the same changes in
streamflow between present and future by also showing the number of quaternary catchments and
corresponding percentage change in streamflow (Department of Water and Sanitation 2019)
ratio changes of 1.1 to 1.5) over the eastern two-thirds of the country, and 50–100%
in the western one-third. The exception is the extreme southwest, where a decrease in
design streamflows is projected when the daily output from multiple GCMs is used
in the ACRU model with techniques to analyze extreme values (Schulze 2011). The
following issues were highlighted in the study:
• As the return period increases from two through five and 10 to 20 years, the
rate of increase in design streamflows decreases and becomes less pronounced,
irrespective of duration (i.e., irrespective of duration of 1 or 7 days).
• The regions within South Africa where the greatest increases in design stormflows
are projected are the transitional areas between summer and winter rainfall regions
where inconsistent weather patterns are likely to be experienced in future.
• On a local scale, as the return period increases from 2 to 20 years, the area in the
southwest expands where decreases in design streamflows are projected.
• For a given return period, the spatial patterns of change into the intermediate
future do not vary among the 1-, 2-, 3-, and 7-day durations, i.e., the changes in
design streamflow appear to be sensitive to return period, but not to duration.
The mean annual streamflow is likely to increase for both the intermediate future
and more distant future since projections indicate higher rainfall events, particularly in the high altitude eastern parts of the basin. Projected increase in mean
annual streamflow is likely to be significantly larger than those projected for mean
annual precipitation because both increases and decreases in rainfall are amplified.
According to Knoesen et al (2009), studies show that variability in streamflow is
projected to increase more in the distant future than the intermediate future. Such