Dams and Water Scarcity

Dams are the paramount driver of hydrological alteration in the U.S., homogenizing regional river dynamics and biodiversity. However, dams also provide a range of economic and social benefits, increasing human resilience against climate variability and change. Under scenarios of increasing water scarcity due to climate forcing and over-allocation of freshwater resources, examining how dams can provide engineered resilience in social-ecological systems is a question of crucial importance. Here we build on a recent interdisciplinary framework referred to as eco-engineering decision scaling that focuses on the collaboration between water resource engineering and river conservation ecology. We ask two questions: (i) Where are the battlegrounds of water scarcity in the U.S., defined as basins where dams have a disproportionately high impact on hydrological and ecological alteration, and thus where modifying dam operations could offer particularly high benefits?, and (ii) How can we identify optimal trade-offs between maximizing water conservation in reservoirs (to increase human resilience to water scarcity) and securing as much biodiversity insurance as possible? The first question will be assessed via a U.S.-wide spatial analysis of dam location, size, and type; hydrological alteration over the last decades (1950-2015); and decoupling between downstream hydrographs and fish communities’ life histories. The second question will be examined via a case study in the Colorado River Basin, using recent advances in time-series methods on long-term streamflow and fish monitoring data. These two questions combined will allow testing in a rigorous quantitative framework the hypothesis that dams can provide engineered resilience in social-ecological systems via controlled river flow manipulations.