An open-source scoping model to generate adaptive policies to manage the Colorado River for uncertain future hydrologic, demand, and ecosystem conditions

Abstract:

Colorado River managers face a deeply uncertain future. Projections of declining watershed runoff are likely to necessitate restructuring of the present interpretation of the Law of the River that allocates water supply among Mexico and the seven states of the Basin. Additionally, the magnitude and distribution of consumptive uses of water will change. Outcomes for river and reservoir ecosystems are poorly predicted. Stakeholders with substantial technical and budgetary resources use the Colorado River Simulation System (CRSS) to explore alternative long-range strategies to manage Colorado River water supplies and demands. This proprietary software represents the water supply and river network with 12 reservoirs, 29 inflow nodes, and 520 water user objects.

We are building an easy to use scoping model that adequately represents the water system to empower a broader range of river stakeholders to adaptively manage the river and its reservoirs. The scoping model is smaller (2 largest reservoirs, Lakes Mead and Powell, 2 inflow nodes, and 2 water user objects), faster (1/100 the run time of CRSS), and open-source (written in Python). The model can simulate adaptive policies (pathways) among numerous water supply, demand, and operations scenario combinations to identify system sensitivity and vulnerability to uncertain future conditions. It helps generate better signposts and alternative policies when system performance becomes undesirable. The scoping model can also link to other open source river ecosystem simulation models for better resolution of those aspects of the system.

We validated scoping model results against CRSS outputs. Scoping modeling results show the incremental effects of major management paradigms such as equalizing storage in Lake Powell and Lake Mead, drought contingency plan operations, Fill Mead First, Fill Powell First, and combinations. The scoping model complements existing simulation models by offering greater flexibility and speed to set up scenarios for uncertain future conditions and generate adaptive policies. This work supports the Future of the Colorado River project.