Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : The role of agriculture expansion in water resources depletion in central Iran

Auteur : Abou Zaki, Nizar

Université de soutenance : University of Oulu

Grade : Doctoral Dissertation 2020

Résumé partiel
In arid and semi-arid regions, water is considered as the main resource for agriculture and therefore for the mainstay of rural societies. In this study, agricultural water usage sustainability in Fars Province, Zayanderud and Bakhtegan Basins, in central Iran was evaluated. The study areas have witnessed a depletion in main river flows and groundwater levels, directly affecting the water security and the well-being on the local inhabitants. Available and developed drought indicators such as : Standardized Precipitation Index (SPI), Stream Drought Index (SDI), Overall Agricultural Drought Index (OADI) and Agricultural Drought Index (ADI) were used. This indicators in addition to remote sensed and in-situ data were used to monitor the water depletion in these areas. Results indicated that both Fars and Zayanderud went through three sustainability water usage stages during a period of 40 year : 1) a sustainable phase, where the water usage matched the water renewability capacity ; 2) a transition phase, where water usage occasionally exceeds the water renewability capacity ; 3) an unsustainable phase, where there is a lack and depletion in water resources for agriculture and domestic usage. Climatically there was no significant distribution of meteorological drought, and no negative trends in the annual precipitation, in Fars and Zayanderud. A hyper-arid climate prevailed for an average of 32 percent of the Fars province spatio-temporal coverage during the study period. The area increased significantly from 30.6 percent in the first decade, 1977 till 1986 to 44.4 percent in the last decade, 2007–2016. In Zayanderud the hyper-arid cold climate was dominant in the study period, with an average 57.5 percent frequency of occurrence. Most of the years, 86 percent of the period from 1977 till 2016, are considered to be wet and normal years meteorologically, and the climatic diversity remained constant with no significant negative trend in Fars. In contrary, the hydrological drought occurrence increased significantly from 30 to 73 percent of the years, especially after the 1980s when the irrigation expanded and 60 percent of the rainfed areas were converted to irrigated areas. This exerted a substantial pressure on surface and groundwater resources for irrigation purposes, led to groundwater depletion in major aquifers in Fars and Zayanderud, reaching 50 meters in some aquifers, and zero flow in the downstream of main rivers. This decrease in the downstream flow of the Zayanderud and Kor Rivers led to the decrease in the surface volume of Gavkhuni Wetland and Bakhtegan Lake.

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