Exploratory Modelling of Multi-sectoral Anthropogenic Drought Vulnerability in Colorado’s West Slope Basins Under Different Climate Scenarios

Abstract

Colorado’s West Slope Basins (CWSB) represent an important source of water for the Southwest U.S., a function that has increased in significance since the onset of the Millennium Drought. During the first two decades of the 21st century, annual streamflow averaged 19% below the 20th century mean, and climate projections suggest that further reductions in streamflow remain an important concern. This challenge on water management under climate change in the West Slope Basins is further complicated by high human water consumption, intricate institutional water management structures, and regulatory frameworks governing water allocation and water rights. As a response to growing human-induced pressure on global water systems, recent studies have introduced the concept of anthropogenic drought, defined as a period of below-normal water availability, stemming from the interaction between natural factors and anthropogenic influences. This research utilizes StateMod, a local water allocation and water rights administration model, to examine natural and anthropogenic influences on streamflow in CWSB. By integrating detailed local water demand data with two synthetically generated climate ensembles, we provide a more comprehensive understanding of the human-induced contributions to drought vulnerability in CWSB. Our results indicate that the anthropogenic impact on water resources intensifies with climate change, leading to unprecedented drought magnitudes. Additionally, a substantial anthropogenic impact on historical streamflow is highlighted, particularly during low flow conditions. The climate change scenario reveals a significant impact on deliveries to Lake Powell, a critical reservoir in the Upper Colorado River Basin (UCRB) which fulfills water supply obligations to downstream regions. These findings enhance our understanding of human influence on water resources and offer guidance for developing sustainable water management strategies in Colorado’s West Slope Basins and other regions facing similar hydrological challenges.