Climate Change Projections

The Intergovernmental Panel on Climate Change (IPCC) provides through its data distribution centre (http://ipcc-ddc.cru.uea.ac.uk/) results from seven General Circulation Models (GCMs). Somewhat arbitrarily, we have selected to use the model from the Hadley Centre for Climate Prediction and Research, referred to as HadCM3, and one from the Max Planck Institute für Meteorologie, referred to as ECHAM4. Since the GCM provides output at a low level spatial resolution, down-scaling to local conditions was essential. Details about the downscaling of GCM results to the seven basins is described in detail in Chapter 2. For the historical data

Fig. 10.3. Projected climate changes according to the two GCMs and the two Special Reports on Emissions Scenarios considered.

series, the East Anglia Climate Research Unit (CRU) database was used to provide data on temperature and precipitation for all seven basins over the 1961-1990 time slice (New et al., 2000). This database provides a consistently interpolated global land surface dataset, with for each month between 1901 and 1996 an average value on a 0.5° X 0.5° grid.

From the various existing statistical transformations that ensure GCM and historical data have similar statistical properties, we used the method developed by Alcamo et al. (1997). For temperature, absolute changes between historical and future

GCM time slices are added to measured values, while for precipitation, relative changes between historical and future GCM output are applied to measured historical values. More details about this approach can be found in Chapter 2.

Figure 10.3 shows that for the near future (2010-2039) a small increase in temperature can be expected of about 0.5°C, while for the distant future (2070-2099) this increase will be between 2 and 3°C. The two GCMs considered are both showing the same trend, although HadCM3 projections are a little bit higher than the ECHAM4 ones. It is interesting that, especially for the A2 scenarios, an increase in variability can be expected.

Precipitation projections are less clear, but the overall trend is a somewhat wetter situation and simultaneously more variation in annual precipitation. However, HadCM3 shows an increase in this variation in the near future, but a decrease in the more distant future.

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