Quantifying the freshwater needs of conservation targets in the Central Valley of California: How much water will they need and what are the trade-offs?

Background/Question/Methods

Transformation of California’s Central Valley into an intensively cultivated landscape has required a water capture and delivery infrastructure that has severely limited the freshwater available for natural communities. Balancing the water needs of ecosystems, wildlife, and people requires strategies that are specific about when and where water is needed most for our conservation targets. To inform our freshwater conservation strategies, we conducted a Freshwater Needs Assessment for California’s Central Valley. Our overarching question was how much water is needed at specific times and places to conserve aquatic ecosystems and to supply water for wildlife-friendly agriculture and wetlands? We were also interested in the potential trade-offs among focal species and habitats given limited water supplies. We used stream flow models, combined with empirical stream flow gage data, to quantify current flow conditions and assess these relative to the flow related habitat requirements of a suite of focal species. In addition, we quantified the water volume requirements needed to meet regional goals for wetlands and waterbird-friendly agriculture. Based on a synthesis of these data, we are developing flow and water delivery recommendations that have the potential to effectively balance the competing water needs of nature and people.

Results/Conclusions

Current patterns of water flows and availability in the Central Valley are dramatically different than those under which native aquatic communities evolved across the Central Valley. In most watersheds water availability from natural runoff has not changed and is sufficient to provide the flow conditions and habitat requirements of focal aquatic species or communities. We identify a limited set of key flow-related habitat characteristics that will be most important for supporting diverse riverine communities. Managing for these flow parameters will require recreating general flow patterns in space and time that mimic historic seasonal and inter-annual variability, rather than delivering more water or a specified percent of historic flows. In isolation, this would be achievable in such a highly managed system. However, given the conservation goals to maintain large areas of managed wetlands and waterbird-friendly agriculture that require large quantities of water from the same managed rivers, there will be significant trade-offs associated with meeting these conservation goals as well as maintaining current deliveries for irrigated agriculture. We use our results to illustrate these trade-offs and some options for balancing competing needs to illustrate how synthesis of existing data and science can be used to inform large-scale management and policy.