Orange–Senqu River Basin Transboundary Diagnostic Analysis
2.5 Climate change
© Connect 4 Climate/Relebohile Marou
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The rain season of 2011 was exceptional throughout the basin, with some areas receiving three or four times more rain than on average. Such extreme events are likely to become more common with climate change.
According to the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (IPCC, 2007), Africa is expected to experience more rapid warming than the global average during the 21st Century, with the drier subtropics warming more than the moist tropics. It was stated that rainfall in southern Africa is likely to decrease in much of the winter rainfall region and western margins. The likelihood of change in summer rainfall, which is most significant for the Orange–Senqu basin, is less evident. Global climate change (GCC) models use a very coarse resolution and cannot take into account local climatic variations. Their application to a single river basin or part of one, even when the basin is as large as the Orange–Senqu, is of little practical value. A global climate change downscaling exercise was recently carried out for the Orange–Senqu basin (ORASECOM, 2011c) with the aim of investigating possible climate change at a higher level of resolution through regional downscaling. 2.5.1 GCC downscaling for the Orange–Senqu River basin
The ORASECOM study (2011c) used both dynamic and statistical downscaling methods with a large volume of climate data from all four basin states. The downscaling used the A1B emission scenario (IPCC, 2000), which assumes a globalised world emphasising economic growth and a balanced dependence on fossil and non-fossil fuel energy sources. The future projections compare the period 2031–2060 with 1971–2000. Projected temperature increase is unevenly distributed across the seasons. In summer and autumn a temperature increase of more than 2.5° C is estimated in the northern part of the basin and Namibia in general. The largest increase of 3° C is predicted for the summer months in the Southern Kalahari Savannah area. The study also looked at the possible changes to precipitation. Figure 33 shows how the long-term average of the precipitation for the future time period may differ from the present. A major decrease in precipitation is predicted for much of the basin, especially the north-eastern part. However, an increase over the source areas, mainly in the Maloti Mountains of Lesotho, is also predicted. It should be stressed that the recommendations of the study emphasised the need both for further downscaling work and improved data in order to achieve a better level of confidence in findings. 2.5.2 Vulnerability to climate change
The IPCC report on regional impacts of climate change (Watson et al. 1998), argues that the vulnerability of a region depends to a great extent on its wealth, and that poverty limits adaptive capabilities. In simple terms, vulnerability is highest where there is ‘the greatest sensitivity to climate change and the least adaptability’. However, it can also be argued that adaptive capability is better where people are already used to adapting to highly variable climatic conditions, as is the case in many parts of the Orange–Senqu basin. Given the huge natural areal and temporal variation of precipitation, especially in the more arid western parts of the basin, it has proved difficult to detect change in precipitation as a result of climate change at a statistically significant level. The vegetation and land-use practices in the basin have, arguably, been adapted to prolonged drought and climatic extremes for many decades and are thus less vulnerable than might be anticipated.