The Role of Environmental Flows in the Spatial Variation of the Water Exploitation Index

Abstract

This article presents a novel methodology to assess the spatial and temporal variations of water resources exploitation within regulated river basins. The methodology, which is based on the application of a basin management model to properly assess the consumed and available water, was applied to a case study in the Iberian Peninsula to analyze the effects of environmental flows in the water resources exploitation of all rivers in the basin. It was demonstrated that the river sections in the upper part of the Órbigo River are subjected to lower water stress levels, so that they would be more suitable alternatives to supply new possible water uses. In addition, it was found that, during the summer months, the available water resources in natural regime are more than 1.5, 1.8 and 2.4 times lower than the consumed water in the upper, lower and middle stretches of the Órbigo River, respectively. This reveals the necessity of regulating the water resource to fulfill the water demands of the basin throughout the year. Finally, it was found that increases (decreases) in environmental flows not only lead to reductions (rises) in water availability, but also can induce decreases (increases) in consumed water resources due to lower (greater) water availability. This effect is more significant as water stress levels are higher. The results of this paper highlight the importance and usefulness of basin management models to accurately estimate the spatial variability of the water exploitation index, and the effects of environmental flows on both water availability and consumed water resources. The proposed approach to reduce the spatial scale of the water exploitation index is also helpful to identify the best water sources in river basins to meet future demands and/or higher values of environmental flows.