The Zambezi River Basin is expected to experience a significant warming trend over the next century. The general consensus emerging from modeling suggests an increase of 0.3-0.6° C per decade. Figure 9 shows observed and simulated trends in temperature for the previous century, and projected temperature trends over the next century for Southern Africa.

Figure 9. Trends in temperature for Southern Africa. The black line shows observed temperatures, 1906-1999. The range of temperatures simulated by IPCC climate models for the observed period are shaded red; those for the projected period, 2001-2100, are shaded orange. The bars at the end of the area shaded orange represent the range of projected scenarios for 2091 to 2100 in relation to estimated carbon dioxide (CO2) emission (low in blue, medium in orange, and high in red). With permission from IPCC (2007a).

Direct observations over the period 1960-2000 in Southern Africa indicate a warming trend of 0.1-0.3° C per decade. Under a medium to high emissions scenario (A1B) from the Special Report on Emissions Scenarios (SRES),1 and using the average of 20 GCMs for the period 2080-2099, annual mean surface air temperature is expected to increase by 3-4° C relative to the 1980-1999 period, with less warming in equatorial and coastal areas (Christensen et al, 2007). Other models (e.g., Ruosteenoja et al. 2003), assuming more intensive use of fossil fuels and corresponding emissions, indicate warming over this period up to 7° C for Southern Africa (which equates to approximately 0.7-1.0° C per decade). Downscaled regional climate models predict smaller but still significant temperature increases for Southern Africa (Kamga et al. 2005). Temperature increases are projected to be most significant for the highly arid south/southwestern portions of the Zambezi River Basin. Climate models for Southern Africa predict more significant warming during the winter months than summer. Hudson and Jones (2002) forecast a 3.7° C increase in mean surface air temperature in summer (December to February) and a 4° C increase in winter (June to August) by 2080.2

1. The Special Report on Emissions Scenarios of the IPCC (Nakićenović et al., 2000) describes four climate global emissions scenarios that relate future greenhouse gas emission levels to key driving forces:

2. Major climate simulation models and their sources for this analysis include the CSIRO2 (Commonwealth Scientific and Industrial Research Organisation, Australia), HadCM3 (Hadley Centre for Climate Prediction and Research, UK), CGCM2 (Meteorological Research Institute, Japan), ECHAM (Max Plank Institute for Meteorology, Germany), GISS-NASA (U.S. National Aeronautics and Space Agency/ Goddard Institute for Space Studies), GFDL (U.S. Department of Commerce/NOAA/Geophysical Fluid Dynamics Laboratory) and PCM (National Center for Atmospheric Research, U.S.).