SIMULATED EFFECTS OF FUTURE CLIMATE ON WATER AVAILABILITY AND PROTECTED SPECIES HABITAT IN A PERENNIAL WETLAND, SANTA BARBARA COUNTY, CALIFORNIA

The potential effects of future climate and changing hydrologic conditions on water availability for aquatic habitat of five protected species (two fish, an amphibian, and two plants) in Barka Slough are evaluated through numerical simulations. Barka Slough is a historically perennial wetland at the downstream, western end of the San Antonio Creek valley watershed. Streamflow, stream disconnection, and depth to groundwater are key habitat metrics for protected species in Barka Slough, especially during seasonal reproductive periods. A previously published integrated hydrologic model of the watershed (simulating water years 1948–2018) was extended to include water years 2019–21 and modified to simulate two versions of future years 2022–51. The two versions of future models were constructed with different climate inputs: 1) a repeated historical climate and 2) the 2070-centered Drier Extreme Warming climate (2070 DEW). The model with 2070 DEW climate conditions has warmer temperatures and an increase in average annual precipitation, driven by more frequent large precipitation events, than the model with historical climate. In both future models, there is a cumulative loss in groundwater storage in and around Barka Slough, a decrease in mean monthly streamflow at Barka Slough, seasonal stream disconnection with the aquifer, and declining groundwater levels. Changes in future mean monthly streamflow volume is unlikely to affect habitat conditions for any of the protected species in either future climate scenario. Both future model versions simulate a transition in Barka Slough from a consistently perennial wetland to a consistently ephemeral wetland. The three key habitat metrics were evaluated during seasonal reproductive periods for each species. Simulated streamflow is not likely to negatively impact any of the five species. Simulated future stream disconnection may negatively impact one of the fish. Future groundwater level decline in the 2070-DEW climate scenario may negatively impact the two plants—in this climate scenario groundwater levels are consistently below the root zone.