CALIFORNIA’S FOURTH CLIMATE CHANGE ASSESSMENT San Diego Region Report Coordinating Agencies: CALIFORNIA’S FOURTH CLIMATE CHANGE ASSESSMENT Introduction to California’s Fourth Climate Change Assessment alifornia is a global leader in using, investing in, and advancing research to set proactive climate change policy, and its Climate Change Assessments provide the scientifc foundation for understanding climate- related vulnerability at the local scale and informing resilience actions. The Climate Change Assessments directly inform State policies, plans, programs, and guidance to promote effective and integrated action to Csafeguard California from climate change. California’s Fourth Climate Change Assessment (Fourth Assessment) advances actionable science that serves the growing needs of state and local-level decision-makers from a variety of sectors. Tis cutting-edge research initiative is comprised of a wide-ranging body of technical reports, including rigorous, comprehensive climate change scenarios at a scale suitable for illuminating regional vulnerabilities and localized adaptation strategies in California; datasets and tools that improve integration of observed and projected knowledge about climate change into decision- making; and recommendations and information to directly inform vulnerability assessments and adaptation strategies for California’s energy sector, water resources and management, oceans and coasts, forests, wildfres, agriculture, biodiversity and habitat, and public health. In addition, these technical reports have been distilled into summary reports and a brochure, allowing the public and decision-makers to easily access relevant fndings from the Fourth Assessment. • A concise summary of the Fourth Assessment’s most important fndings and conclusions. • An in-depth report on how California’s people, built KEY FINDINGS environment, and ecosystems will be impacted by climate change and how we can proactively adapt, based on the Fourth Assessment’s fndings. • Reports summarizing Fourth Assessment fndings to STATEWIDE SUMMARY provide a state of the science for nine regions, the ocean and coast, tribal communities, and climate justice in California. SUMMARIES FOR REGIONS AND COMMUNITIES • Academic research that provides robust and detailed results on resilience and vulnerability to climate change. ORIGINAL RESEARCH TO • A shared foundation of updated climate change INFORM POLICY AND ACTION projections, data and ecosystem models developed for use by Assessment authors to permit cross-comparability of results and ensure the fndings consider a robust range ASSESSMENT FOUNDATION: UPDATED CLIMATE PROJECTIONS AND DATA of future climate conditions. These data are available to the public via Cal-Adapt.org. All research contributing to the Fourth Assessment was peer-reviewed to ensure scientifc rigor as well as, where applicable, appropriate representation of the practitioners and stakeholders to whom each report applies. For the full suite of Fourth Assessment research products, please visit: www.ClimateAssessment.ca.gov Fourth Climate Change Assessment San Diego Region | 2 CALIFORNIA’S FOURTH CLIMATE CHANGE ASSESSMENT San Diego Region CLIMATE NORTH JUSTICE COAST REGION SACRAMENTO TRIBAL VALLEY COMMUNITIES REGION SIERRA SAN FRANCISCO NEVADA BAY AREA REGION REGION SAN JOAQUIN VALLEY REGION CENTRAL COAST OCEAN REGION AND COAST COMMUNITIES INLAND DESERTS LOS ANGELES REGION REGION SAN SAN DIEGO DIEGO REGION REGION The San Diego Region Summary Report is part of a series of 12 assessments to support climate action by providing an overview of climate-related risks and adaptation strategies tailored to specifc regions and themes. Produced as part of California’s Fourth Climate Change Assessment as part of a pro bono initiative by leading climate experts, these summary reports translate the state of climate science into useful information for decision-makers and practitioners to catalyze action that will beneft regions, the ocean and coast, frontline communities, and tribal and indigenous communities. The San Diego Region Summary Report presents an overview of climate science, specifc strategies to adapt to climate impacts, and key research gaps needed to spur additional progress on safeguarding the San Diego Region from climate change. Fourth Climate Change Assessment San Diego Region | 3 CALIFORNIA’S FOURTH CLIMATE CHANGE ASSESSMENT San Diego Region Authors COORDINATING CONTRIBUTING Sarah Giddings Amber Pairis LEAD AUTHORS AUTHORS Scripps Institution Scripps Institution of Oceanography, of Oceanography, Julie Kalansky, Tom Amabile UC San Diego UC San Diego, Scripps Institution San Diego County of Climate Science Alliance, Emergency Services Kristen Goodrich of Oceanography, Tijuana River Ntl Estuarine South Coast UC San Diego Puja Batra Research Reserve David Pierce Batra Ecological Strategies Scripps Institution Daniel Cayan, Mike Grim Rachel Clemesha City of Carlsbad of Oceanography, Scripps Institution Scripps Institution UC San Diego Kristen Guirguis of Oceanography, of Oceanography, Alexandra D. Syphard UC San Diego UC San Diego Scripps Institution of Oceanography, Conservation Biology Jef Crooks UC San Diego Institute LEAD AUTHORS Tijuana River National Lan Wiborg Estuarine Research Reserve Jeremy Haas CA Regional Water Quality City of San Diego Kate Barba, Laura Engeman Control Board, SD Adam Young Scripps Institution Scripps Institution Jefrey Heys Scripps Institution of Oceanography, of Oceanography, of Oceanography, UC San Diego US Forest Service UC San Diego UC San Diego Reinhard E. Flick Robert Leiter Stay Cool for Grandkids Allison Young Laura Walsh, Scripps Institution San Diego Association of Oceanography, Megan Jennings of Governments San Diego Regional UC San Diego, San Diego State University Climate Collaborative California State Parks Bonnie Ludka Alexander Gershunov Scripps Institution Kimberly Brouwer, Scripps Institution of Oceanography, UC San Diego of Oceanography, UC San Diego UC San Diego Danielle Boudreau, Tijuana River National Estuarine Research Reserve CITATION: Kalansky, Julie, Dan Cayan, Kate Barba, Laura Walsh, Kimberly Brouwer, Dani Boudreau. (University of California, San Diego). 2018. San Diego Summary Report. California’s Fourth Climate Change Assessment. Publication number: SUM-CCCA4-2018-009. Disclaimer: This report summarizes recent climate research, including work sponsored by the California Natural Resources Agency and California Energy Commission. The information presented here does not necessarily represent the views of the fnding agencies of the State of California. Fourth Climate Change Assessment San Diego Region | 4 CALIFORNIA’S FOURTH CLIMATE CHANGE ASSESSMENT Acknowledgements San Diego has a diverse community of researchers, planners and land manager that contributed to this report through writing sections, sharing thoughts in meetings, and reviewing drafs of the various sections. Te report was supported by the NOAA Regional Integrated Sciences and Assessment Program (RISA), which funded J. Kalansky and D. Cayan, and the California Energy Commission, which supported D. Cayan and D. Pierce. We would also like to thank the San Diego Regional Climate Collaborative for supporting L. Walsh in contributing to the report and Scripps Institution of Oceanography Center for Climate Change Impacts and Adaptation for supporting K. Barba. Te Climate Science Alliance, South Coast, with additional support from the Southwest Climate and Adaptation Science Center, was instrumental in providing venues and organization for discussion between climatologists and ecologists. Additionally, we would like to thank San Diego Gas and Electric for kindly hosting the author and stakeholder group for a meeting to review the preliminary results and discuss the regional knowledge and coordination gaps which were used to develop the fnal section of the report. We also ofer sincere thanks to numerous not named contributors who participated in discussions and provided material and advice. Fourth Climate Change Assessment San Diego Region | 5 CALIFORNIA’S FOURTH CLIMATE CHANGE ASSESSMENT Highlights San Diego County will be increasingly afected by climate change and has begun to prepare on multiple fronts for the panoply of climate change related impacts on San Diego County’s residents, development, infrastructure, and ecosystems. In future decades, San Diego County and adjacent regions will be confronted with, among others, increasingly warmer average temperatures, more frequent and likely more intense heat waves, more intense droughts, occasionally increased heavy rainfall events and foods, continuing Santa Ana winds and wildfre threats. Te impacts will play out in diferent ways across the complex terrain and difering climates within San Diego County. Communities along San Diego County’s 70 miles of coastline are planning for substantial sea level rise, which will afect beaches, sea clifs, real estate, infrastructure and other amenities. Te region has many unique characteristics, such as narrow beaches backed by sea clifs, large percentage of conserved lands, highly populated urban and suburban development, small farm dominated agriculture, and large solar power production; these characteristics, among others, all determine vulnerabilities to climate change and related adaptation measures. Below are some highlights of climate impacts, adaptations and gaps. • Temperature is projected to increase substantially, by 5˚F to 10 ˚F by the end of the 21st century. Along with mean temperature, heat wave frequency