Groundwater footprint methodology as policy tool for balancing water needs (agriculture & tourism) in water scarce islands - The case of Crete, Greece

•A novel approach for groundwater footprint estimation was introduced that incorporates water quality.•A case study in the water scarce island of Crete was presented.•From the 11 groundwater systems in Crete, three have iGF/A values above one (Chania, Iraklio, and Sitia).•The average value of iGF/A for all aquifer systems in Crete is very good (0.649).•Adaptation measures and water policies in agricultural and urban sectors were presented.

In many Mediterranean islands with limited surface water resources, the growth of agricultural and touristic sectors, which are the main water consumers, highly depends on the sustainable water resources management. This work highlights the crucial role of groundwater footprint (GF) as a tool for the sustainable management of water resources, especially in water scarce islands. The groundwater footprint represents the water budget between inflows and outflows in an aquifer system and is used as an index of the effect of groundwater use in natural resources and environmental flows. The case study presented in this paper is the island of Crete, which consists of 11 main aquifer systems. The data used for estimating the groundwater footprint in each system were groundwater recharges, abstractions through 412 wells, environmental flows (discharges) from 76 springs and 19 streams present in the area of study. The proposed methodology takes into consideration not only the water quantity but also the water quality of the aquifer systems and can be used as an integrated decision making tool for the sustainable management of groundwater resources. This methodology can be applied in any groundwater system. The results serve as a tool for assessing the potential of sustainable use and the optimal distribution of water needs under the current and future climatic conditions, considering both quantitative and qualitative factors. Adaptation measures and water policies that will effectively promote sustainable development are also proposed for the management of the aquifer systems that exhibit a large groundwater footprint.

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