Making thirsty cities sustainable: A nexus approach for water provisioning in Quito, Ecuador.

In view of accelerated climate change and urban demographics, balancing human and ecosystem needs for water resources is a critical environmental challenge of global significance. Since water, agriculture, health, and energy are inextricably linked, sustainable development goals (SDGs) actions in one policy area commonly have impacts on the others, as well as on the ecosystems that natural resources and human activities ultimately depend upon. Managing urban water supply systems therefore requires a nexus approach that integrates goals across sectors, reduces the risk that SDG actions will undermine one another, and ensures sustainable resource use. We developed a transdisciplinary methodological framework based on a Pareto frontier analysis to define the sustainable solutions of a multi-objective optimization among four competing criteria, water provision, water quality, energy cost, and biodiversity conservation. The study was applied to three mountainous headwater basins in the Ecuadorian Andes, which provide around 30% of Quito's total water supply. We found that an optimized management of water intake structures would meet current consumption needs while reducing the probability of emergence of water pathogens and limiting the impact on aquatic biodiversity by 30% and 9% respectively, without any increase in energy costs for pumping water from other sources. Nonetheless, under future scenarios of climate change and water demand, higher energy consumption, and therefore an increase in operating costs, would be needed to meet urban demand and preserve environmental conditions. Overall, the range of Pareto optimal water supply strategies across the water-health-energy-biodiversity nexus provides valuable information for decision makers and offers support for achieving sustainable management of water resources.

Linking global climate change to local water availability: Limitations and prospects for a tropical mountain watershed.

Bridging the gap between the predictions of coarse-scale climate models and the fine-scale climatic reality is a key issue of hydrological research and water management. While many advances have been realized in developed countries, the situation is contrastingly different in most tropical regions where we still lack information on potential discrepancies between measured and modeled climatic conditions. Consequently, water managers in these regions often rely on non-academic expertise to help them plan their future strategies. This issue is particularly alarming in tropical mountainous areas where water demand is increasing rapidly and climate change is expected to have severe impacts. In this article, we addressed this issue by evaluating the limitations and prospects in using regional climate models for evaluating the impact of climate change on water availability in a watershed that provides Quito, the capital of Ecuador, with about 30% of its current water needs. In particular, we quantified the temporal and spatial discrepancies between predicted and observed precipitation and temperature, and explored underlying mechanisms at play. Our results provide a strong critique of the inappropriate use of regional models to inform water planning with regard to adaptation strategies to face climate change. As a multidisciplinary group composed of hydrologists, ecologists and water managers, we then propose a framework to guide future climate change impact studies in tropical mountain watersheds where hydro-climatological data are scarce.