The National Water Balance

Abstract

Tunisia’s rainfall resource is 36 km³/year, generating flows for 4.8 km³/year as blue water. Groundwater withdrawals are 2 km³, and many aquifers are overexploited: the national groundwater overexploitation is 20%. The chapter presents updated information on water facilities: large dams, hill lakes and hill dams, water-table and deep aquifers, with a focus on weakly renewable resources and exploitable resources taking into account the water salinity criterion. The water resource of rainfed agriculture (green water), is 13 km³/year, increasing to 19 km³/year when including rangelands. The total blue water withdrawals are 3.0 km³, of which 0.64 km³ for municipalities and 2.2 km³ for irrigation. Coastal areas are more populated and require water from other better-endowed regions: the whole country is marked by large water transfers from West to East. The infrastructure includes comprehensive resource monitoring, in relation to groundwater whose exploitation increased 3.5 times over the past 40 years. A specific section is devoted to the anthropogenic water cycle, where a precise assessment of all water uses is provided: from withdrawals, through allocations and actual uses, to consumptive uses and returns to the receiving environment. The last part establishes the complete water balance of Tunisia, with a first prognosis of all rainfall resources processing.