A new approach to calculate the water exploitation index (WEI+)

The Water Exploitation Index (WEI), or withdrawal ratio, is an indicator of water scarcity, which has been updated into its WEI+ form by the Committee of Experts of the European Commission. In calculating the total abstraction of fresh water, this indicator also includes the possible return flow and management rules. The demand for freshwater and long-term freshwater resources are both necessary to calculate the WEI+. These values are not easy to assess at basin or sub-basin level and, for this reason, WEI values are generally calculated at the country level. This paper introduces a new approach to calculate the WEI+, with the purpose of extending its use to basin and sub-basin levels. The methodology is based on flow duration curve estimation, which evaluates freshwater resources, and a Web-GIS system that evaluates water abstractions distribution. This approach allows for the assessment of locally stressed areas in the hydrographic network and could provide a fundamental step toward more comprehensive regional water resources management plans. The new methodology is tested in some sub-basins of the Upper Tiber River Basin (Italy). These results contribute to the analysis of water withdrawals sustainability, based on the policy of the European Environment Agency, which is aimed toward the development of a proactive approach for reducing water stress.