What is your opinion about the influence in agriculture of some indicators, such as aridity index or plant comfort index?

The arid zone is a geographical and climatic reality and our ancestors naturally adapted to it. This figure shows a shot of the olive groves of Chaal in Sfax (Tunisia): Olive trees as far as the eye can see, cultivated without the slightest drop of irrigation water, produce Olive-Oil of exceptional quality under rainfall of less than 250 mm per year. The same goes for Pistachio trees in Iran, Fig trees, and Almond trees... around the Mediterranean, all cultivated under rainfed conditions.

Figure source: A Conceptual Model for National Water Security in Water-Scarce Countries, By Jamel Chahed International Workshop on Water Security and Technology Innovation in Hydro-Environmental Engineering July 13, 2023. Available on:

"National water security– Case study of an arid country, Tunisia (Authors: Besbes, Chahed Hamdane), Springer (2019) 4:11". The Previous French version of the book is available in chapters on:

https://www.researchgate.net/publication/356650449_Securite_Hydrique_de_la_Tunisie_Preface_Introduction https://www.researchgate.net/publication/356662490_Les_Problemes_de_l'Eau_dans_le_Monde

The comprehensive water balance expresses the amount of virtual water associated with food products trade and defines a "Water Dependency Index" (WDI), which represents the part of net virtual water in the total food demand water equivalent. This assumes that the allowance in Blue Water to irrigation must adjust to the available water once the direct needs insured.

The Food Demand Water Equivalent (FDWE) includes water equivalent of Agricultural Production consumed on the local market and the water-equivalent of agri-food imports. The water equivalent of agricultural production includes green water-equivalent and blue water equivalent.

The "Water Dependency Index" (WDI) defined by Besbes et al. (2002, 2010) represents the net equivalent of Virtual Water volumes (Imports-Exports) within the total food demand and is expressed as: WDI = (IMP-EXP) / FDWE.

If one refers to international literature, the concept of water dependency, as defined by FAO (2003), relates only to blue water; it expresses the external renewable water resources (originating outside the country) as a percentage of the total renewable water resources (internal and external). This definition has been largely used by the scientific community as well as by international organisations.

Based on water footprint concept, Hoekstra and Mekonnen (2012) defined the ‘virtual water import dependency’ of a nation as ‘the ratio of the external to the total water footprint of national consumption’ where total ‘water consumption’ refers to the ‘water needed for the production of the domestic demand for goods and services’. The indicator is conceived to reflect the extent to which a country relies on imports of water in virtual form. The results reported by Hoekstra and Mekonnen (2012) on water dependency give, as it may be expected, high values for water-scarce countries (like Jordan 86%, Israel 82%, Yemen 76%, Lebanon 73%). These results reveal however some striking points; in particular, some water-rich countries such as Italy, Germany, the United Kingdom, and The Netherlands have surprisingly high water dependency indexes between 60–95%.

By relating the Water Dependency Index to agricultural water, the indicator proposed by Besbes et al. (2002, 2010)attempts to go beyond the appraisal of the water dependency level of nations to specify the balance sheet items related to the national food demand. As the net equivalent of virtual water represents the difference between the total food demand water equivalent and the total food production water equivalent, the Water Dependency Index (WDI) could be more explicitly detailed in order to bring out the different contributions to food production: "Blue Water" referring to the use of ground and surface water as well as non-conventional water resources, "Green Water" referring to the water reserves of the soil effectively used in crop production or into direct grazing, and "Virtual Water" referring the flux of the "net virtual water import". The objective is to consider the extent to which greater value for all water resources could be achieved.

As the major part of water resources is directly or indirectly used in food production, the WDI related to food balance is in itself sufficient to reflect the National water security by measuring the level to which a nation relies on foreign water to ensure its food demand. This indicator could be consolidated by financial indicators, for instance, the coverage rate of the agri-food trade balance. The improvement of the food security of a country expressed in terms of WDI will depend on the capacity of the country to improve food productivity either in the irrigated sector (Blue Water, including non-conventional water resource) as well as in the rain-fed agriculture and direct grazing (Green Water). From this point of view, the WDI appears as a major decision-making tool for sustainable water resources management. It is also a learning tool as well as a 'discussion-support' tool that provides a common platform for the coherence of the activities of different actors and stakeholders.

Besbes, M., Chahed, J., & Hamdane, A. (2019). Food and water management in Northwest Africa. The Oxford Handbook of Food, Water and Society, 426.

Besbes, M., Chahed, J., & Hamdane, A. (2019). National water security: case study of an arid country: Tunisia. Cham, CH: Springer.

Hamdane, A., Chahed, J., & Besbes, M. (2014). Sécurité Hydrique de la Tunisie: Gérer l'eau en conditions de pénurie. Sécurité Hydrique de la Tunisie, l'Harmattan, Paris.