Sustainable management of water in an arid region: water supply measures compared

An expanding global population, with competing demands for water from domestic, industrial and agricultural users, particularly in arid regions, is placing an ever greater strain on water resources. This scarcity also threatens the availability of water needed to sustain aquatic and terrestrial ecosystems. The Segura Basin in southeast Spain is one such water-stressed region. It receives around 400 mm of rain a year and periodically faces droughts.

There is insufficient water to meet annual demand of around 1483 Mm3 (million cubic metres). Local surface water availability, mainly stored in reservoirs, is only around 318 Mm3 in an average year. To meet the annual water demand for crop irrigation (about 1117 Mm3 ), urban consumption (336 Mm3 ) and water allocated to maintain ecosystem functions (30 Mm3 ), water is transferred to the region via the pipes, canals, aqueducts and tunnels of the Tajo-Segura water transfer system and supplied from saltwater desalination plants.

Any further local water deficits are met by extracting groundwater. Some aquifers are carefully controlled, and a balance is maintained between recharge and extraction. However, others are overexploited.

This study investigated the environmental impact of alternative means of supplying water for irrigation, urban and environmental purposes in the region. It used a life cycle approach, covering the construction, operational and dismantling phases of supply, to compare the impact of two external sources: the Tajo-Segura water transfer system and seawater desalination.

It also compared the impact of using two local water sources – natural surface waters and groundwater resources. Environmental impact was judged in terms of damage to human health and ecosystems, and resource availability. Additionally, the researchers estimated the life cycle impact of water used in urban areas (including drinking water and wastewater treatment), for irrigation and for the environment, to see whether expanding supply options would be feasible, as current rates of local water depletion are unsustainable. For example, water used for drinking purposes requires the construction of plants and infrastructure to make the water fit for consumption and wastewater from industry needs to be cleaned before being returned to the environment.

Furthermore, uncontrolled extraction of groundwater (used for irrigation) can reduce the amount of water available to aquatic and terrestrial ecosystems. Using information from public authorities and previous research, the researchers developed four scenarios of water availability:

(i) a base case derived from an average year’s (2009) water demand and water supply; (ii) a good rainfall year; (iii) a drought year; and (iv) a year with almost no water arriving from the Tajo-Segura water transfer system due to operational problems.