Climate Change and Water in Africa

1. Climate Change and Waterin Africa UNDP ACCRA

2. HAE Model- Integrated Assessment Emission Scenario Climate Outcome Agronomic Response Hydrologic Response Economic Outcome

3. Hydrology • Exact impact on hydrology is basin specific (e.g. Revelle and Wagner 1983, Gleick 1987, Lettenmeier et al 1992) • Depends on change in local temperature and rainfall- both are uncertain • Depends on characteristics of basin • Global analysis implies need for basin studies around the world

4. Watershed Changes That Lead to Impacts • Changes in mean annual flow • Increased evapotranspiration (increasing demand for water) • Changes in seasonal flows (earlier runoff) Gleick 1987, Nash and Gleick 1993 • Changes in peak flows (floods) • Changes in interannual variance

5. Evaluating Water Impacts • Need to determine demand for water by use (urban, industrial, mining, farming) • Aggregate demand functions • Equate aggregate demand with supply • Water allocation inefficient if marginal value varies across users • Optimal allocation equates marginal values

6. Water Adaptation • Climate change will shift demand and supply of water • Allocations across users must change given new demand and supply • If new marginal values are not equated, damages can be large

7. Urban and Industrial Use Price Of Water Welfare Loss Poor Adaptation Agriculture Use U0 A1 A0 U1 Water

8. Adaptation • Reallocate water from low to high valued use • Implies equating marginal value of water across users • Reduces magnitude of loss

9. Urban and Industrial Use WELFARE CHANGE WITH ADAPTATION Price Of Water Gain Loss Agriculture Use A1 A0 Water U0 U1

10. Water Allocation Methods • Who pays for reductions depends on who owns the water, not on who reduces use • If government owns water, users lose whenever water is taken away • If current users own water, others must pay them to take it. Current users cannot be made worse off.

11. California Hydrology Lund et al 2006 • SAC-SMA hydrology model • 6 basins: Smith, Sacramento, Feather, American, Merced, Kings • HADCM2 2090 (+3.3C, +58%P) • PCM 2090 (+2.4C, -21%P)

12. Runoff ResultsHadley 2090 Flow Smith, Sacramento, Feather, American Baseline Apr Oct Month Flow 2090 Merced, Kings baseline Month Oct

13. Runoff ResultsPCM 2090 Flow Smith, Sacramento, Feather, American Baseline Apr Oct Month Flow 2090 Merced, Kings baseline Month Oct

14. Runoff Conclusions • Hadley- 2090- increase of 11%- mostly winter flow • PCM- decrease of 9%- some Nov-Dec and some May-July

15. Change in Water DemandAdams 2006

16. CALVINLund et al 2006 • Reallocates water to maximize economic benefits • Flow constraints, dams • Urban values of water • Operating costs • Does not consider changing infrastructure • Assumes perfect foresight

17. CALVIN Results(Million $/yr)

18. CALVIN CONCLUSION • Wetter climate scenario leads to benefits and dryer scenario leads to damages • Reallocating water to highest use reduces welfare effects • Institutional and infrastructure constraints keep costs high

19. Water Institutions • Need to be more efficient today • Climate change likely to increase urgency of reforms • Two major approaches to allocation: Improve centralized control or strengthen water rights and allow water trading