Abstract

The Aculeo Lake is an agricultural and touristic hotspot of the Metropolitan Region of Chile, which used to store water and provide ecological services. This lake completely disappeared by May 2018, due to an unknown fast-drying process, which started in 2010, increasing the competition among different actors and finally, generating social and environmental conflicts. The environmental disaster highlighted the lack of mitigation and adaptation plans to severe water scarcity, the limited water management, and the late response to continuous reductions in water availability and increases in water demand. Typically, top-down approaches have been implemented to evaluate causes and adaptation options under water scarcity crises. These types of decision-making approaches fail at incorporating stakeholders' participation and views, a fundamental aspect of the hydrological cycle. A combination of top-down and bottom-up approach was followed to co-construct a hydrological model along with stakeholders and decision makers, to support a collaborative dialogue process regarding causes and alternatives to deal with water scarcity. The hydrological model built with active contribution from the community, was used to respond to the causes of the drying by estimating the catchment water balance and the levels of the lake under 14 different water management strategies. Then, key community stakeholders participated in: validating the hydrological model for the water balance; defining the water management strategies; and evaluating and prioritizing the management strategies (before and after modeled). Results show that the lake disappearance was caused both by water consumption and the megadrought (present in central Chile since 2010), being the later the most important factor, with annual precipitation deficits of about 38%, since the megadrought. Preferred water management alternatives were discussed pre and post modeling to observe changes in preferences. This work shows how integrating a top-down and bottom-up approach, with closer collaboration with stakeholders and decision makers can improve our understanding of the hydrological cycle in intervened basins, and support policy-society dialogues on water management problems and possible solutions.