Abdelkader Hamdane

Changing Water Resources and Food Supply in Arid Zones: Tunisia

The notion of water security in an arid country takes on another dimension when the comprehensive water balance concept is applied to water used by rain-fed agriculture and to the water equivalent of international food exchanges. In the case of Tunisia, this concept expands the prospects for improvements in national food security by optimizing the food balance and the corresponding virtual water flux. It also prompts reconsideration of criteria and indicators classically used to characterize water stress situations. The current situation shows that about 30% of the water used in Tunisia is imported as food (virtual water); that number is likely to reach 40–50% in 2025 due to climate change, diet change, demographic growth, and improved water management. Asia and North Africa will most likely not be self-sufficient in terms of food production and will need to import food from other continents (e.g., South America). Africa, however, could be self-sufficient if its existing water resources are developed. Bioenergy production is likely to be limited to a small fraction of the global energy needs. Major food shortages in cases of severe global droughts (e.g., during very strong El Nino events) may occur, however, with severe consequences in terms of food availability.

Virtual-water content of agricultural production and food trade balance of Tunisia

This article is devoted to the assessment of Tunisian agricultural production and food trade balance water-equivalent. A linear regression model relating annual rainfall to crop yields is developed to estimate the agricultural production water-equivalent. Its implementation is based on national data for crop and animal production, leading to food demand water-equivalent quantification. Results highlight the relationship between agricultural and water policies and provide a picture of food security in the country in relation to local agricultural production, and to virtual water fluxes related to foodstuffs trade balance.

National Water Security

ion of freshwater resources is at the basis of much of the social and economic development of humanity. But the real renewable freshwater resources of the Earth are represented by precipitations on the continents (Fig. 1.1). Estimated at about 110,000 km3/year on land, they perpetuate the renewable water resources of the Earth. These flows feed the continental hydrological cycle in its natural and human parts, the main term of which provides continental evaporation and evapotranspiration: through the soil water reserves, this term sustains life of continental ecosystems, and allows the development of rainfed agriculture. According to the soil moisture content and its texture, the rest of rainwater is subdivided into: (i) runoff to rivers and surface water systems, (ii) infiltration in the soil and at depth to aquifers. At the regional level, the continuous mapping of the soil water reserves is used to establish the link between meteorological and hydrological information with applications in the fields of: (i) agriculture, by detecting plant water needs for irrigation monitoring; (ii) urban hydrology and flood forecasting in case of extreme runoff conditions; (iii) hydrological and climate modeling, at regional and global scales. For all these applications, and in the same way that there are approved global networks of rainfall gauging stations, a global soil moisture database is taking place (Robock 2011). The soil water reserve makes the link between the amount of water precipitated on land, the available energy and the carbon cycle. In terms of food production and ecosystem functioning, it is the soil water resource which, by means of solar energy and generation of photosynthetic products, determines the Terrestrial Net Primary Fig. 1.1 Average annual precipitation, 1960–1990, mm/year; (based on data fromwww.worldclim. org, consulted on 2 June 2011) 8 1 The World Water Issues Table 1.3 Terrestrial soils occupation and net primary production (Adapted from Michigan University 2017) Ecosystem Extension 106 km2 TNPP dry matter 109 ton/year HTNPP dry matter 109 ton/year HTNPP (%) Forests 40 48.7 13.5 28 Prairies and Rangelands 35 52.1 11.6 22

Water Security, Food Security and the National Water Dependency

Water requirements for food demand in Tunisia have more than tripled over the past four decades, and amount to more than 16 km3 in 2010. As the population has nearly doubled during the same period, water requirements for individual dietary recorded an increase from about 1050 m3/year/capita in the early 1970s to nearly 1600 m3/year/capita in the late 2010s. To draw up an outlook of water-balance future, long term perspectives for all kinds of water resources are carried out with various demographic hypothesis. The blue water evolution relies on substantial increase of non conventional water and stronger water uses control. The blue water footprint of crop productions will rise from 1.4 km3 in 2010 to 2.1 km3 by 2050. At the same time, green water involved in food production is expected to increase by almost 25%. With the medium variant of demographic projection, the water balance deficit would be around 13 km3 in 2100 and the water dependency index, ratio of imported virtual water minus the exported one divided by the water equivalent of the food consumption, will increase from 39% in 2010 to 48% in 2100. With higher population hypotheses, the water dependency index could reach 62%, and perhaps even more under the global warming effect.

The National Water Balance

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.

Fifty Years of Water Policies, 1960–2010

Tunisia has implemented a network of hydraulic facilities allowing to ensure safety about drinking water supply of the whole urban population and a large part, although unequally, of rural regions. Irrigation has been developed on 420,000 ha, or 8% of arable land which contribute nearly a third of the agricultural production value. The water facilities are involved, in addition, to mitigate the flood-related damage and droughts. Urban sanitation has also developed favorably in large cities, but yet very unevenly in rural areas. All these achievements have contributed to improve food and health conditions. However, this development admits an objective limit which is the threshold of exploitable resource. The policy of increasing supply of conventional resources begins to reach its limits and corollaries of accelerated water resources development were clearly identified since the early 1990s: overexploitation of many shallow and deep aquifers, water salinization in some of them, soil salinization in some irrigated areas. In this context, integrated management of the resource including demand management, is introduced to meet the growing needs expressed by various sectors. Important changes are taking place and reforms are being implemented to protect water resources, control production and use of non conventional water resources, better manage hydrological risks, anticipate conflicting sectoral interests by mobilizing all stakeholders, modernize the regulatory framework and develop appropriate planning.

On the Water Security Concept: State of the Art

This chapter attempts to place the reader in tune with current trends, debates and sometimes contradictions that dominate the issue of water on a global scale. A historical overview traces the progress of water status, describes the international community action in addressing the water issue and analyzes the implementation of the right to water. It is followed by a review of water security and water scarcity assessments methods focussing on the progress achieved towards more holistic approaches which go beyond conventional assessments of water availability and water scarcity, to include the multiple dimensions of water security. At National scale, water security is a central political issue for which public authorities develop appropriate strategies to secure supply for all uses and promote human well-being through socio-economic development. These aspects fall within the concept of National Water Security with its “soft” and “hard” components. The essential elements of a framework that conceptualizes the National Water Security concept are developed, with particular emphasis on the arid and semi-arid countries. Considering water scarce regions, the starting point of National Water Security is to raise awareness on the limits of the resource in order to guarantee the natural environments conservation and the protection of the resource.

The World Water Issues

The chapter introduces to concepts and debates that dominate the water issue at the global scale. First, the world water balance outlines contributions made to the development of understanding renewable freshwater resources on Earth, as well as withdrawals and impact of human actions on the hydrological cycle. The water footprint concept applied at global scale makes it possible to specify the respective places occupied by blue, green and virtual water in the world budget. A second part focusses on water balance of arid countries. The following part deals with impacts of anthropogenic activities on water resources, particularly acute in arid countries where strategies of massive resource mobilization and transfers are faced with problems related to water scarcity and competing demands. The perspective of climate change exacerbates an already critical situation in some countries under water stress: increased exploitation, quality deterioration, overexploitation, soils and aquifers salinization, negative impacts of dam reservoirs on groundwater recharge. The last part presents the main principles, concepts and instruments of water policies. Among the basic principles should be mentioned the user pays and polluter pays principles, the precautionary principle and the principle of subsidiarity. As regards the instruments, different approaches are presented: integrated water resources management, water demand management, watershed-based management, participatory management. Mention is also made of aspects relating to the economic dimension of water, value and pricing, as well as water data and water information systems.

The Holistic Water Balance: Blue Water, Green Water and Virtual Water

The chapter considers the detailed water balance related to food needs of Tunisia. The water footprint of agricultural production, including rainfed crop production, irrigated agriculture and animal production is estimated on average at 12 km3/year. Overall, the green water contribution, including rangelands, represents three quarters of the agricultural production. The remaining corresponds for a half to blue water footprint associated to irrigation and for the rest to virtual water imports embedded in fodder and cereals for livestock production. Assessment of virtual water fluxes associated with food products trade shows that virtual water imports has increased significantly in recent decades going from less than 2 km3/year to more than 8 km3/year from 1970 to 2000. Simultaneously, virtual water exports have doubled, from 1 km3/year to over 2 km3/year. Green water share represents more than 75% of the virtual water exports, and the share of BW represents 12%, more than half of which from dates exports. The virtual water coverage ratio, (exports to imports), has gradually deteriorated, from 80% in the early 1970s to 30% in the late 2000s.

Water Security in Tunisia: Debated Issues

The chapter addresses some of water issues still being debated, for which no definitive solution has yet been seriously considered, and have not yet obtained a consensus among water experts, water actors and the civil society. The questions that preoccupy Tunisia serve to organize the debate around two main topics: (i) How to secure the water supply? This theme covers physical and technical issues that Tunisians, engineers and decision-makers traditionally know how to formulate and resolve, but divergences persist concerning opportunities, timelines, methods of approach and implementation. This topic includes: new ways to improve the national water balance, underground storage of surplus water from the wetter North, internal security of water resources and hydraulic facilities, coping with groundwater overexploitation, securing water quality, protecting the status of water and human health. (ii) How to achieve good water governance? This theme covers legislative, institutional, regulatory and cognitive issues, most of which are subject to wide-ranging debates initiated some twenty five years ago by the Tunisian water community. These issues, still open to debate, concern: the institutional reforms, the Water Code revision, how to better use water for more equity and efficiency, developing and better valuing the knowledge on water, sustainably manage transboundary basins by consultation mechanisms.