An Integrated Approach to Identification, Assessment and Management of Watershed-Scale Risk for Sustainable Water Use Through Reuse and Recycling

Water resources are essential to development, not only economically but also socially, politically and ecologically. With growing demand and potentially shrinking supply, water scarcity is one of the most pressing socio-ecological problems of the 21st century. Considering implications of global change and the complexity of interrelated systems, uncertain future conditions compound problems associated with water stress, requiring hydrologic models to re-examine traditional water resource planning and management. The Copiapó water basin, located in the Atacama Desert of northern Chile exhibits a complex resource management scenario. With annual average precipitation of only 28 mm, water intensive sectors such as export agriculture, extensive mining, and a growing population have depleted the aquifeŕs reserves to near critical levels. Being that global climate change models predict a decrease in already scarce precipitation, and that growing population and economies demand will likely increase, the real future situation might be even worse than that predicted. A viable option for alleviation of water stress, water reuse and recycling has evolved through technological innovation to feasibly meet hydraulic needs with reclaimed water. For the proper application of these methods for resource management, however, stakeholders must possess tools by which to quantify hydrologic risk, understand its factors of causation, and choose between competing management scenarios and technologies so as to optimize productivity. While previous investigations have addressed similar problems, they often overlook aspects of forecasting uncertainty, proposing solutions that while accurate under specific scenarios, lack robustness to withstand future variations. Using the WEAP (Water Evaluation and Planning) platform for hydrologic modeling, this study proposes a methodology, applicable to other stressed watersheds, to quantify inherent risk in water management positions, while considering uncertainties in supply (climate change), demand (market variations), and measurement (risk definition). Applied to the Copaipó case study, this methodology proposes the solution of a 30% demand decrease within the agricultural sector through urban wastewater recycling and increased irrigation efficiency.