Global Results

In 1995 global freshwater withdrawals were approximately 15% of global runoff. The geographical distribution of supply and demand leads to regions of excess and regions of scarcity. Thus any 'global' analysis of climate change impacts on the water system are misleading, as the global mean temperature increases are averages of regions with significantly more and significantly less warming. Any single 'global' indicator of climate change impacts on water resources is a very crude measure of the impacts. In this section we will report on a series of hydro-climatic parameters calculated by the models. These are growing season, potential evapotranspiration and effective precipitation, crop water deficit and available irrigation water supply. These variables are presented for the globe as a very crude measure. To provide some further insight and geographic resolution, these variables are presented separately for the developed and developing regions of the world.

Figure 12.2 shows that globally there is very little change from the base conditions for actual crop evapotranspiration and water available for irrigation. However, globally there is a significant decrease in effective precipitation and thus an increase in water deficit. These results show that rain-fed agriculture will be impacted more than irrigated agriculture.

Results were aggregated into developed and developing regions. The results show that the developing regions are more strongly impacted. There is a greater decrease in effective precipitation and a greater increase in water deficit which is not made by the small increase of available water.

Fig. 12.2. Global water analysis of climate change in the 2080s relative to current climate.
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