Global Climate Change Scenario

T h e effect of changing climate on water resources is one of the most difficult global environmental changes t o assess. Problems arise because:

1. A changing climate may affect both availability and use.

2. A changing level of water availability would have an impact on water quality.

3. T h e distribution of climate-induced impacts would differ significantly from region t o region.

4. T h e available results of climate models are not consistent with their predictions.

T h e last point can be illustrated with the help of the preliminary results for Egypt.[3] Various simulations of the Nile River flow, under a climate

Four attributes of climate change are particularly relevant in the context of regional vulnerability:

1. Changes in atmospheric variables, such as temperature, precipitation, and wind speed.

2. Inter-year variability in precipitation and temperature, leading t o ex- treme events such as droughts and floods.

3. Intra-year variability in precipitation and temperature.

4. A rise in sea level.

T h e change in the atmospheric variables would affect the relationships t h a t govern water needs, as well as river flow. Occurrences of droughts and floods can also alter a region's water availability and demands.

8 0 World Water Resources and Regional Vulnerability In this study, it was assumed that the total effect of climate change would be realized by the year 2025. Although most climate studies suggest that the likely time when these effects would be realized is 2060, population forecasts for this year are sketchy. However, this assumption, although not accurate, would provide us with an accurate impact on regional vulnerability, since if a country is vulnerable under climate change at its 2025 level of population, it is undoubtedly going t o be vulnerable under the higher (2060) level of population.

In this study it was assumed that all regions of the world would face the same impact from a global climate change. On the availability of water, it was assumed that the warming earth would increase the evaporation, which would decrease availability by 10 percent of the 1990 level in all regions some water is required in the process and, therefore, may not be affected by the climate change; part of the water for industrial use is recirculated and, therefore, may not be affected by climate change.

Two scenarios were simulated: (1) countries used agricultural water in a manner similar t o Scenario 3, without food self-sufficiency; and (2) countries pursued the goal of food self-sufficiency by converting rain-fed cultivated areas into irrigated areas. Under both scenarios, population and industrial growth was assumed t o be a t the level of Scenario 3.

Caution is advised in the interpretation of results, since the impacts of climate change assumed in the study are hypothetical and may bear no re- semblance t o the situation in 2025 for various parts of the world. Nonetheless the results illustrate the challenge facing some countries under the assumed conditions.

5 . 5 . 2 Results on vulnerability of regions without

food self-sufficiency

Because of decreases in available supply, many countries would face water related problems. Results for various study regions are shown in Table 5.12.

Even if various countries do not pursue the goal of food self-sufficiency, a changing climate would create water-related problems for 47 countries, many of which are located in Middle East Asia, Northern Africa, Southern and Northern Europe, and Southern Africa. However, some regions, such as

Table 5.12. Relative water availability and use under the global climate change scenario, in 202.5.

Use- Use-availability Per capita (m3) availability ratio under food Study region Availability Use ratioa self-sufficiency

North America 12,926 2,799 22 2 2 unaffected in terms of vulnerability t o water resources.

Although a s a n aggregate large continental countries, such a s Canada, t h e USA, a n d t h e former USSR, seem t o escape the brunt of climate change, many regions within these countries may become more vulnerable. For ex- ample, t h e prairie region of C a n a d a and t h e midwestern states a n d California in the USA show signs of water stress or even scarcity under this scenario.

Similarly, the newly created nations of Armenia, Moldavia, Azerbaijan, a n d the Ukraine may become water vulnerable regions.

5 . 5 . 3 Scenario 4A: Vulnerability of regions

with

food self-sufficiency

W i t h t h e food self-sufficiency goal, a s shown in Table 5.12, water-related problems may arise in several regions. Regions with a significant increase in t h e use-availability ratio include Central America, the USSR, Europe

82 World Water Resources and Regional Vulnerability (Southern and Eastern), Sahel Africa, and Japan. In these regions, food self-sufficiency may be attained but perhaps at a high price.

In addition to a warming climate, occurrences of extreme events, par- ticularly droughts, may prevent the achievement of food self-sufficiency in many regions. The timing and the amount of precipitation can be important determinants of whether the goal of food self-sufficiency is realized.

T h e current situation and the situation under a climate change are pre- sented in Figures 5.6 and 5. '7, respectively. Under current conditions, water is constraining economic activity in only a few countries. This situation is markedly different from that in the year 2025 when countries face population growth, increased industrial activity, and climatic changes. The countries that are most vulnerable are in Northern Africa and the Middle East. How- ever, many regions in Asia and Africa are also vulnerable under a climate change.

Notes

[I] Theoretically, such a n assumption is not totally correct, because food production requires inputs, sorne of which are produced by nonagriculture industries. As food production increases, t h e demand for farm inputs would also increase. This, in t u r n , will increase t h e use of water for industrial purposes.

[2] In reality, this assumption is not very practical. We have ignored the possibility t h a t not all lands may be irrigable a n d , furthermore, there may not be adequate financial resources t o develop irrigation projects.

[3] Based on personal communications with Professor Ken Strzepek, University of Colorado, Boulder.

World Water Resources and Regional Vulnerability