1. The Fifth GEF Biennial International Waters Conference, Cairns, 26-29 October 2009 Global Changes and Water Resources Workshop The Merguellil catchment (central Tunisia): towards an integrated study of water resources and water uses Christian LEDUC Gestion de l'Eau, Acteurs, Usages IRD, UMR G-EAU, Montpellier, France leduc@ird.fr

2. Impacts of the Global Change on the hydrological cycle An attempt to integrate studies at a relevant scale A situation typical of the Mediterranean environment (and many othersemi-arid cases) GEF International Waters Conference, Cairns, Oct. 2009, Global Changes and Water Resources Workshop

3. National context: limited resources, highly variable in time and space increasing demand for population, agriculture, tourism decision of a maximum use of WR (goal of nearly 100 %) Regional context: semi-arid catchment (> 2000 km 2 ) increasing uses up to overexploitation water export to the coastal region GEF International Waters Conference, Cairns, Oct. 2009, Global Changes and Water Resources Workshop Kairouan

4. Global change Rainfall: 200 to 550 mm.yr -1 highly variable: ex 1969 no long-term trend Increasing population (0.25 % yr -1 1994-2004 2.3 % yr -1 1984-1994) Intensified agriculture grazing lands turned into fields traditional crops replaced by irrigated crops Many water and soil conservation works Big dams GEF International Waters Conference, Cairns, Oct. 2009, Global Changes and Water Resources Workshop

5. Water and soil conservation works Increasing number of Water/Soil Conservation works (bench terraces, 48 small dams) For limitingerosion on the slopes silting up of the big El Haouareb dam Rarely in agreement with local customs and wishes Increase in green water, locally Increase in stored water (small reservoirs) Clear decrease in blue water at the catchment outlet Fundamental maintenance of WSCW: quick loss of efficiency final result often worse than nothing Limited development of new uses from the new storages 2003 1970 1988 GEF International Waters Conference, Cairns, Oct. 2009, Global Changes and Water Resources Workshop

6. The El Haouareb big dam Protection against floods + Provision of water to an irrigated scheme Total change in groundwater recharge (location, processes, flow, quality): - no river flow downstream - the dam is often dried up - ≈ 60 % of the dam water infiltrates to the karst - tracing of the reservoir evaporation (reservoir, downstream)

7. Groundwater upstream 3 "small" aquifers 1 deliberately overexploited by the State for exporting drinking water to the coast Enhanced leakage from the rivers to the aquifers Increasing pumping for irrigation and potable water Groundwater upstream 1 thick aquifer, overexploited for potable water, public and private irrigation No enforcement of the law protecting the aquifer

8. Some technical remarks Contradictory impacts of conservation works: prevent siltation but decrease the exploitable water resource The big dam is often empty, because of the unexpected karstic loss Physical models propose contradictory explanations Possible consequences of overexploitation: deeper pumping more difficult and more expensive resort to more salted water GEF International Waters Conference, Cairns, Oct. 2009, Global Changes and Water Resources Workshop

9. Socio-economical surveys Typology of farms and farmers Behaviour of farmers facing changes in their physical environment (climate, soil fertility) in the regulations (law, water price, technical constraints) in the external market Cooperation/competition between farmers (land rental, water sale) (family vs speculators, large vs small) Spatial scales of benefit: personal-local-regional-national

10. GEF International Waters Conference, Cairns, Oct. 2009, Global Changes and Water Resources Workshop Socio-economical surveys Proposal of measures for protecting the water resource acceptability - efficiency Unexpected impacts: increasing irrigated areas after subsidising drip irrigation Social equity vs profitability Institutional analysis lack of coordination inside the same Ministry limited involvement in local top-down associations

11. Conclusion To manage together water supply and water demand To integrate technical and socio-economical aspects To build long-term sustainable proposals Natural and human complexity beyond our models Already in official files: interconnection of big dams in Central Tunisia transfer channels from Northern Tunisia GEF International Waters Conference, Cairns, Oct. 2009, Global Changes and Water Resources Workshop

12. Second International Conference on Climate, Sustainability and Development in Semi-arid Regions - ICID 2010 Fortaleza, 16-20 August 2010 www.icid18.org Contribution to the Rio+20 UN conference on development and environment 1) Climate and Environment 2) Climate and Sustainable Development 3) Governance and Sustainable Development 4) Policy Processes and Institutions. Submissions of papers, panels, round tables welcome