Tunisia is on the Mediterranean coast of North Africa, midway between the Atlantic Ocean and the Nile Delta. The country has two distinctive Mediterranean coasts, west-east in the north, and north-south in the east. Despite its relatively small size (163 610 km2), great environmental diversities are observed due to its north-south extent.
Tunisia ranks in the category of countries with the least resources water in the Mediterranean. For a population of 11 million, the total renewable water resources per capita is estimated to 415 m3 (2014) and is largely under the penury threshold of 1000 m3. This value is set to gradually decrease to 350 m3 in 2030.
In Tunisia, water resources were evaluated in 2000 to 4825 Millions of Mm3, with 2700 Mm3 of surface water and 2125 Mm3 of ground water. The scarcity is enhanced by a high spatio-temporal variability related to the influence of two climate types, Mediterranean in the North and Saharian in the South. Water resources in Tunisia are marked by both availability and quality problems.
Surface water resources are limited because of the semi-arid to arid climate of the country with episodic droughts, and because of the salty rocks found within the country. Surface waters are distributed over three natural areas according to climatic and hydrological conditions. The north provides relatively regular contributions representing 82% of the total surface water potential while covering only 16% of the country. The center part, covering 22% of the area, is characterized by irregular resources. It provides 12% of the total surface water potential. The southern part of the country which accounts for approximately 62% of the total area, providing very irregular resources representing 6% of the country’s total potential of water. The salinity of surface water varies according to the origin of the resource. Only 72% of the surface water resources, mainly located in the northern part of the country (82%), have salinity less than 1.5g/l and could be considered of good quality.
Groundwater resource are confined within 212 shallow aquifers and 267 deep aquifers most being nonrenewable. As surface water, groundwater is characterized by unequal spatial distribution and variable quality in terms of salinity. The north has 55% of the shallow groundwater resources and only 18% of the deep groundwater resources. The center provides 30% of the shallow resources and 24% of the deep resources. The south provides 15% of the shallow resources and has 58% of the deep resources. Low salinity is found in only 8% of shallow water and 20% of deep aquifers. 36% of groundwater resources is considered as salty with more than to 3g/l and is therefore unsuitable for agricultural sector and for the production of drinking water.
The Tunisian national strategy centers around three major points:
- The management of the demand: a question of preserving the resource, ensuring economic efficiency, and preserving social equity by a good water distribution
- The integrated management of the resources: the use of groundwater during periods of drought, the recharge of groundwater to face problems of overdraft and degradation, and the use of treated waste water and brackish water
- Resource and environmental protection: quantitative conservation through reinforcement and improvement of water capture and storage, qualitative conservation of water resources and ecosystems through pollution reduction, monitoring, and cost evaluation
In order to ensure equality of water distribution, improve drinking water quality and set up a short and long term strategy for water storage, transfer and economical management of the various interconnected catchments, the Ministry of Agriculture invested in devising a digital master plan to simulate and compare water resource needs for the different sectors to the available water for different time horizons. The model is based on the introduction of projected cases of production and usages. Thus, the simulation can take into account several criterion to determine the water balance: (1) the demand development perspective by considering several trends for each sector of demand, (2) the initial storage in dams and the available resources in groundwater, (3) the type of the hydrologic year defined by the manager as being average dry or wet, (4) the possibility of mixing water with different salinity coming from different water bodies, (5) planning horizon and time step simulation.