Trade-off between irrigation demands and environmental flows requirements in Spain

Providing adequate water supply following the development of society and ensuring the good status of water-dependent ecosystems is becoming increasingly complex. This is particularly relevant in areas characterized by water scarcity and with unfavourable projections due to climate change, such as the Iberian Peninsula. Water is fully allocated in many water resources systems, while environmental water requirements are intensified. Consequently, it is fairly probable that in the medium and long term water demands will not be satisfied with the current reliability. This fact may particularly affect to irrigation water supply, as the most important consumptive water use. We are developing a National Research Project entitled: Climate scenarios and adaptation of water resources systems (SECA-SRH). The main purpose is to generate knowledge that contributes to the design and implementation of climate change adaptation policies that consider simultaneously technical, economic, social and environmental aspects. The increase of the comprehension of water system behaviour allows decisions making and prioritizing water uses. This would help to achieve the sustainability of the management of water resources systems in the medium and long term. In this study, as part of the mentioned project, we analyse the effect of different criteria for the allocation of environmental flows on the sustainability of the water resources systems in Spain, in the current situation (1989-2019). The availability of water is estimated as the maximum water demand for population and agriculture (irrigation) that can be supplied with a given reliability in a given location of the river network and satisfying environmental flow restrictions. The methodology is based on the use of the high resolution WAAPA model. 720 dams with a reservoir greater than 1 hm3 and 1948 sub-basins are considered. The calculation is made at each dam, at the confluences of the main rivers and for the aggregate set of each sub-basin. The results show that the availability of water in a system is very sensitive to changes in environmental flow regimes. The relationship between reduction in water availability and environmental flows is unevenly distributed in Spain. This result may suggest that the implications of increasing the allocation of water to environmental flows may vary, depending on the hydrological regime and storage availability.