Climate and land change impacts on future water availability for managed wetland habitat

Background/Question/Methods

Approximately 90% of naturally occurring wetlands in California’s Central Valley have been lost or fragmented because of human land use. Despite this degradation, the region remains a critical North American migratory corridor for wintering waterfowl, sustained through a complex system of managed wetlands and post-harvest flooded agriculture. Climate variability and human water demand directly impact the amount of water available to create this essential habitat. To identify potential habitat availability given projected future climate and land use change, we integrated a hydrologic and water-use model with a spatially-explicit land change model. The Water Evaluation and Planning model, adapted for Central Valley’s waterbird habitat (WEAP-CVwh), was used to model future land use and climate scenarios from 2011 to 2101. The WEAP-CVwh outputs were summarized and ingested as land use transitions and flooding probabilities for the spatially explicit Land Use and Carbon Scenario Simulator (LUCAS) model. We modeled 5 stakeholder-informed scenarios representing varied climate, restoration, and land change, comparing divergent outcomes at 270 m2 resolution, generating annual projections of future land use and flood duration probabilities. This ensemble modeling approach has produced the first future waterfowl habitat maps based on climate-driven water availability, human land-use related water demand, and historical flooding information.

Results/Conclusions

Declining water availability is the dominant driver of habitat loss across scenarios. The hot/dry scenarios showed the greatest declines in January flooded area by 2101—an important month for overwintering waterbirds. In contrast, higher water supplies in wet climates drive perennial cropland conversion which also leads to potential habitat losses. Potential flooded cropland declined (25 and 33%) under warmer/wetter climate conditions due to this conversion to perennial crops, exposing habitat vulnerability. Overall, climate-driven loss of water availability had a greater impact on flooded habitat availability than land-use change. When combined, climate change and the conversion of potentially flooded cropland to perennial cropland will threaten future waterbird habitat particularly in January, the peak of the migratory bird season, even when current habitat restoration goals are met. Our analysis demonstrates that stakeholder-informed scenario analysis can identify target areas for potential habitat change, vulnerability, and conservation. By examining competing demands for water from social and ecological systems under a changing climate, we can better inform land managers as to likely future outcomes for restoration goal setting and mitigation planning.