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Climate Action Plan, Phase 3: Climate Change Vulnerability Assessment

California Department of Water Resources (DWR) | February 14th, 2019

Summary

Climate change impacts have been widely documented globally, across the nation, and within the state. Loss of snowpack; longer, more frequent heat waves; and longer, more

Climate change impacts have been widely documented globally, across the nation, and within the state. Loss of snowpack; longer, more frequent heat waves; and longer, more intense wildfire seasons are already being experienced in California. While uncertainties remain about the exact timing and extent of projected impacts, numerous climate-driven hazards represent a clear threat to Department of Water Resources (DWR) facilities, managed lands, operations, and staff activities. By conducting this department-wide vulnerability assessment, DWR seeks to better prepare its decision-making for an uncertain future. This climate change vulnerability assessment (VA) provides the first evaluation of its kind for facilities owned and operated by DWR and the activities that DWR performs. This analysis draws from the extensive body of knowledge about climate change and attempts to evaluate, describe, and quantify — where possible — DWR’s vulnerabilities to expected increases in wildfire, extreme heat, and sea-level rise, as well as to changes in hydrology and ecosystems that will impact DWR’s facilities, operations, and other activities. Table ES-1 presents examples of vulnerabilities identified in this assessment and summarizes quantitative indicators of climate change risk. Using a mid-century time horizon, climate-change-driven hazards assessed in this VA are presented under six categories: wildfire, extreme heat, sea-level rise, long-term persistent hydrologic changes, short-term extreme hydrologic events, and habitat and ecosystem services degradation. This assessment applies a common framework to examine vulnerability through three components of how DWR’s assets and operations could be exposed to future climate hazards, how these assets and operations are sensitive (or susceptible) to impacts of this exposure, and the capacity of these assets and operations to cope with or adapt to changing conditions or events.

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Climate Change and Future Water Availability in the United States, Chapter E of U.S. Geological Survey Integrated Water Availability Assessment—2010–20

U.S. Geological Survey (USGS) | January 15th, 2025

Summary

The following are the key points of this chapter: The steady rise in global temperature as a result of human activity is causing changes in Earth’s water cycle.

The following are the key points of this chapter: The steady rise in global temperature as a result of human activity is causing changes in Earth’s water cycle. The amount of water stored within and moving between vapor, liquid and frozen components of the water cycle is shifting, with significant consequences for water availability. Climatic drivers underlie regional or local changes in water supply and their socioeconomic impacts. Threats to the quantity and quality of water available for humans and ecosystems in North America include increases in drought, aridification, and fire weather; heavy precipitation and flooding; cryosphere decline; rising surface-water temperatures; and saltwater intrusion in coastal areas. An understanding of how changes in the major climatic drivers impact the water cycle and the accurate simulation of impacts in hydrological models are crucial to predicting future water availability and developing adaptation strategies to ensure human and ecosystem water supplies. Companion chapters: U.S. Geological Survey Integrated Water Availability Assessment—2010–20, Chapter A Water Supply in the Conterminous United States, Alaska, Hawaii, and Puerto Rico, Water Years 2010–20, Chapter B Status of Water-Quality Conditions in the United States, 2010–20, Chapter C Water Use Across the Conterminous United States, Water Years 2010–20, Chapter D Integrated Water Availability in the Conterminous United States, 2010–20, Chapter F

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Climate Change Impacts, Vulnerabilities, and Adaptation in the San Francisco Bay Area: A Synthesis of PIER Program Reports and Other Relevant Research

California Research Bureau (CRB) | July 31st, 2012

Summary

This paper synthesizes San Francisco Bay Area-focused findings from research conducted in 2010–2012 as part of the state’s Vulnerability and Adaptation study sponsore

This paper synthesizes San Francisco Bay Area-focused findings from research conducted in 2010–2012 as part of the state’s Vulnerability and Adaptation study sponsored by the California Energy Commission’s Public Interest Energy Research (PIER) Program. Historical observations of changes already evident are summarized, as well as projections of future changes in climate based on modeling studies using various plausible scenarios of how emissions of heat-trapping gases in the atmosphere may change. Studies synthesized here show how these climate changes increase risks to society and natural ecosystems in a number of ways. Sectors for which impacts, vulnerabilities, and adaptation options are presented include water, agriculture, energy supply and demand, transportation, ecosystems, public health, wildfire, and coastal resources. Results show that depending on the vulnerability of human and natural communities, and their abilities to respond to these growing risks through adaptive changes, the San Francisco Bay Area could experience either significant impacts or maintain its resilience in the face of a rapidly changing environment.

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Climate change increased the likelihood of wildfire disaster in highly exposed Los Angeles area

American Geophysical Union (AGU) | January 28th, 2025

Summary

To determine the role of climate change in this observed trend we combine the observation-based estimates with climate models. Eight of the eleven models examined also

To determine the role of climate change in this observed trend we combine the observation-based estimates with climate models. Eight of the eleven models examined also show an increase in extreme January FWI, increasing our confidence that climate change is driving this trend. Combining models and observations, we find that human-induced warming from burning fossil fuels made the peak January FWI more intense, with an estimated 6% increase in intensity, and 35% more probable.

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Climate change increases risk of extreme rainfall following wildfire in the western United States

American Association for the Advancement of Science (AAAS) | April 1st, 2022

Summary

Post-wildfire extreme rainfall events can have destructive impacts in the western United States. Using two climate model large ensembles, we assess the future risk of ext

Post-wildfire extreme rainfall events can have destructive impacts in the western United States. Using two climate model large ensembles, we assess the future risk of extreme fire weather events being followed by extreme rainfall in this region. By mid-21st century, in a high warming scenario (RCP8.5), we report large increases in the number of extreme fire weather events followed within 1 year by at least one extreme rainfall event. By 2100, the frequency of these compound events increases by 100% in California and 700% in the Pacific Northwest in the Community Earth System Model v1 Large Ensemble. We further project that more than 90% of extreme fire weather events in California, Colorado, and the Pacific Northwest will be followed by at least three spatially colocated extreme rainfall events within five years. Our results point to a future with substantially increased post-fire hydrologic risks across much of the western United States.

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Climate change is increasing the likelihood of extreme autumn wildfire conditions across California

Environmental Research Letters (IOP) | August 20th, 2020

Summary

California has experienced devastating autumn wildfires in recent years. These autumn wildfires have coincided with extreme fire weather conditions during periods of stro

California has experienced devastating autumn wildfires in recent years. These autumn wildfires have coincided with extreme fire weather conditions during periods of strong offshore winds coincident with unusually dry vegetation enabled by anomalously warm conditions and late onset of autumn precipitation. In this study, we quantify observed changes in the occurrence and magnitude of meteorological factors that enable extreme autumn wildfires in California, and use climate model simulations to ascertain whether these changes are attributable to human-caused climate change. We show that state-wide increases in autumn temperature (~1 °C) and decreases in autumn precipitation (~30%) over the past four decades have contributed to increases in aggregate fire weather indices (+20%). As a result, the observed frequency of autumn days with extreme (95th percentile) fire weather—which we show are preferentially associated with extreme autumn wildfires—has more than doubled in California since the early 1980s. We further find an increase in the climate model-estimated probability of these extreme autumn conditions since ~1950, including a long-term trend toward increased same-season co-occurrence of extreme fire weather conditions in northern and southern California. Our climate model analyses suggest that continued climate change will further amplify the number of days with extreme fire weather by the end of this century, though a pathway consistent with the UN Paris commitments would substantially curb that increase. Given the acute societal impacts of extreme autumn wildfires in recent years, our findings have critical relevance for ongoing efforts to manage wildfire risks in California and other regions.

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Climate change threatens California’s future

Public Policy Institute of California (PPIC) | January 31st, 2020

Summary

California faces a twofold climate challenge: finding cost-effective ways to reduce emissions of greenhouse gases (GHGs) and preparing for the changes that are

California faces a twofold climate challenge: finding cost-effective ways to reduce emissions of greenhouse gases (GHGs) and preparing for the changes that are expected even if global emissions fall. Greenhouse gas emissions pose a serious threat. The state experienced 7 of its 10 warmest years on record from 2012 to 2018, and warming is expected to continue. Sea level is predicted to rise 2 to 7 feet on California’s coast by 2100, and the frequency of extreme events such as droughts, heat waves, wildfires, and floods is expected to increase. Higher temperatures result in more precipitation falling as rain (and less as snow), which will increase both the frequency and magnitude of flooding and diminish water reserves in the Sierra snowpack.

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Climate warming enhancement of catastrophic southern California debris flows

Nature Portfolio (Springer Nature) | June 29th, 2020

Summary

The sequence of wildfires followed by debris flows, frequently affects southern California, reflecting its drought-heavy precipitation climate bipolarity. Organic debris

The sequence of wildfires followed by debris flows, frequently affects southern California, reflecting its drought-heavy precipitation climate bipolarity. Organic debris from incomplete burning is lighter than inorganic matter, and partially inviscid. Hence lower rainfall totals can trigger downslope motion than typically required by the underlying clasts of loose inorganic granular material. After advection downslope, the pebble-laden organic debris has a higher capacity for rilling; a positive feedback process. A mechanism is proposed whereby boulders are ‘rafted’ by organic debris. This coordinated movement of boulders greatly enhances the debris flow erosion capacity. This climate change sensitive debris flow enhancing mechanism, through organic–inorganic granular material interaction, is supported by observations and the numerical simulations. Using a model explicitly parameterizing erosion processes, including runoff entrainment, rilling incision, and bank collapse, the lifecycle of the Montecito debris flow of January 9, 2018 is simulated, providing quantitative estimates of mass conveyed and debris sorting at the terminus. Peak rafting speeds are ~ 12.9 m/s at ~ 300 m asl. Total boulder (effective diameter > 25 cm) volume involved for the Ysidro Creek area alone is ~ 5 × 104 m3, scattered between the region 50–260 m asl. Debris flows are highly repeatable and locations prone to debris flows are identified and their likelihood of realization estimated.

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Compounding effects of climate change and WUI expansion quadruple the likelihood of extreme-impact wildfires in California

Nature Portfolio (Springer Nature) | February 21st, 2025

Summary

Previous research has examined individual factors contributing to wildfire risk, but the compounding effects of these factors remain underexplored. Here, we introduce the

Previous research has examined individual factors contributing to wildfire risk, but the compounding effects of these factors remain underexplored. Here, we introduce the “Integrated Human-centric Wildfire Risk Index (IHWRI)” to quantify the compounding effects of fire-weather intensification and anthropogenic factors—including ignitions and human settlement into wildland—on wildfire risk. While climatic trends increased the frequency of high-risk fire-weather by 2.5-fold, the combination of this trend with wildland-urban interface expansion led to a 4.1-fold increase in the frequency of conditions conducive to extreme-impact wildfires from 1990 to 2022 across California. More than three-quarters of extreme-impact wildfires—defined as the top 20 largest, most destructive, or deadliest events on record—originated within 1 km from the wildland-urban interface. The deadliest and most destructive wildfires—90% of which were human-caused—primarily occurred in the fall, while the largest wildfires—56% of which were human-caused—mostly took place in the summer. By integrating human activity and climate change impacts, we provide a holistic understanding of human-centric wildfire risk, crucial for policy development.

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Debris flow occurrence under changing climate and wildfire regimes: A southern California perspective

Geomorphology (Elsevier) | December 2nd, 2022

Summary

In southern California, wildfire incidents are increasing in frequency and magnitude. There is a great deal of research predicting the impact of climate change on large s

In southern California, wildfire incidents are increasing in frequency and magnitude. There is a great deal of research predicting the impact of climate change on large scale fire regimes. These impacts, now the new normal, include increases in future fire incidents and burn severities. Yet predictive studies on how ecosystems respond to changing fire regimes are lacking. Identifying trends in post-fire erosion patterns, such as post-fire debris flows, is critical for increasing human resiliency and adaptation to changing weather patterns and eventual long-term climate change. The relative historical abundance of post-fire debris flows in southern California presents this concern: will worsening wildfire regimes result in more post-fire debris flows? Our research addresses this concern by utilizing a descriptive approach to analyze post-fire debris flows in southern California from 2001 to 2018 to elucidate possible trends. We found that 84 % of debris flows originate from watersheds with soils burnt at moderate soil burn severity. We found that debris flow occurrence is more reliant on the percent coverage of a soil burn severity classification than its areal extent. Further, larger fires also tended to produce more debris flows and most (73 %) debris flow watersheds occurred in predominantly bedrock areas. Our research suggests that the number of post-fire runoff-generated debris flows in the region will increase if fires continue to increase in size, occur on slopes of at least 20°, burn south-facing watersheds with bedrock of igneous or sedimentary origin to at least a moderate severity, and peak rainfall intensity return intervals do not change. These findings highlight the interconnectivity between natural erosive processes, wildfires, humans, and climate change.

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agriculture (1)
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disadvantaged communities (DACs) (2)
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monitoring (2)
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