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Record-breaking summer forest fires have become a regular occurrence in California. Observations indicate a fivefold increase in summer burned area (BA) in forests in northern and central California during 1996 to 2021 relative to 1971 to 1995. While the higher temperature and increased dryness have been suggested to be the leading causes of increased BA, the extent to which BA changes are due to natural variability or anthropogenic climate change remains unresolved. Here, we develop a climate-driven model of summer BA evolution in California and combine it with natural-only and historical climate simulations to assess the importance of anthropogenic climate change on increased BA. Our results indicate that nearly all the observed increase in BA is due to anthropogenic climate change as historical model simulations accounting for anthropogenic forcing yield 172% (range 84 to 310%) more area burned than simulations with natural forcing only. We detect the signal of combined historical forcing on the observed BA emerging in 2001 with no detectable influence of the natural forcing alone. In addition, even when considering fuel limitations from fire-fuel feedbacks, a 3 to 52% increase in BA relative to the last decades is expected in the next decades (2031 to 2050), highlighting the need for proactive adaptations. [ABSTRACT FROM AUTHOR]

This paper presents a methodological framework to evaluate the resilience, with the primary focus on performance degradation, of levee-protected electric power networks to flooding in a changing climate. To this end, a multi-disciplinary framework is established by integrating climate science, hydrology, and electric power network analysis. The framework quantifies the effect of climate change on flood hazard levels in a levee-protected area and the subsequent changes in the resilience of the electric power network. In the first step, the changes in the exposure of levee-protected regions to flooding hazard in a warming climate are calculated. Then, the probabilities of failure of power network components due to flooding under current and projected future climate are determined. Finally, the power system resilience index is used to assess the system resiliency for pre-flooding (baseline), historic flooding, and two projected future flooding scenarios. For demonstration, the proposed framework is applied to a levee-protected area in Northern California. The IEEE 118-bus standard test system is employed to represent the power network in the study area. Results reveal that climate change can considerably decrease the system resilience of the levee-protected electric power network. The findings of this study can contribute towards more resilient power network systems under a changing climate. [ABSTRACT FROM AUTHOR]

Warming temperatures and severe droughts have contributed to increasing fire activity in California. Decadal average summer temperature in California has increased by 0.8 °C during 1984–2014, while the decadal total size of large fires has expanded by a factor of 2.5. This study proposes a multivariate probabilistic approach for quantifying changes to fire risk given different climatic conditions. Our results indicate that the risk of large fires in California increases substantially in response to unit degree changes in summer temperature. The probability of annual mean fire size exceeding its long-term average increases by 30% when summer temperature anomaly increases by 1 °C (from −0.5 °C to + 0.5 °C). Furthermore, the probability of annual average fire size exceeding its long-term average doubles when the annual precipitation decreases from the 75th (wet) to the 25th (dry) percentile. The proposed model can help manage fire-prone regions where fire activity is expected to intensify under projected global warming. [ABSTRACT FROM AUTHOR]

Existing major reservoirs in California, with average age above 50 years, were built in the previous century with limited data records and flood hazard assessment. Changes in climate and land use are anticipated to alter statistical properties of inflow to these infrastructure systems and potentially increase their hydrological failure probability. Because of large socioeconomic repercussions of infrastructure incidents, revisiting dam failure risks associated with possible shifts in the streamflow regime is fundamental for societal resilience. Here we compute historical and projected flood return periods as a proxy for potential changes in the risk of hydrological failure of dams in a warming climate. Our results show that hydrological failure probability is likely to increase for most dams in California by 2100. Noticeably, the New Don Pedro, Shasta, Lewiston, and Trinity Dams are associated with highest potential changes in flood hazard. Plain Language Summary: Dams are critical manmade infrastructure that provide resilience against extremes (e.g., droughts and floods) and regulate water resources. In 2017, California experienced a series of flooding events, which triggered incidents such as structural failure of the Oroville Dam's spillway. Because of the large social and economic impacts of such incidents and given the major dams in California have an average age of above 50 years, it is important to evaluate the risk of failure of dams over a planning period in the future. In this study, we inspected the possible impacts of climate change on the future flooding hazard for several major dams in California. Here we show that in the warmer future climate, the risk of dam failure most likely increases for most of the major dams in California. The insights gained from this study highlight the important role of adaptation strategies for the operational management of aging dams in a changing climate, together with adequate and timely maintenance. Key Points: Flood hazard is projected to increase at the upstream of major dams in California due to changes in precipitation extremesFailure probability is projected to increase for most of the California dams in a warming climateHistorical 100‐year flood is 5 times more likely for some biggest California dams under RCP8.5 (high greenhouse gas concentration levels) [ABSTRACT FROM AUTHOR]

The article focuses on the impact of protracted drought on the structural integrity of earthen levees in California. Topics discussed include the geotechnical engineering perspective regarding the prolonged drought on levees in the Central Valley and Delta region, the resilience of levees, and urban flood control.

The current California drought has cast a heavy burden on statewide agriculture and water resources, further exacerbated by concurrent extreme high temperatures. Furthermore, industrial-era global radiative forcing brings into question the role of long-term climate change with regard to California drought. How has human-induced climate change affected California drought risk? Here, observations and model experimentation are applied to characterize this drought employing metrics that synthesize drought duration, cumulative precipitation deficit, and soil moisture depletion. The model simulations show that increases in radiative forcing since the late nineteenth century induce both increased annual precipitation and increased surface temperature over California, consistent with prior model studies and with observed long-term change. As a result, there is no material difference in the frequency of droughts defined using bivariate indicators of precipitation and near-surface (10 cm) soil moisture, because shallow soil moisture responds most sensitively to increased evaporation driven by warming, which compensates the increase in the precipitation. However, when using soil moisture within a deep root zone layer (1 m) as covariate, droughts become less frequent because deep soil moisture responds most sensitively to increased precipitation. The results illustrate the different land surface responses to anthropogenic forcing that are relevant for near-surface moisture exchange and for root zone moisture availability. The latter is especially relevant for agricultural impacts as the deep layer dictates moisture availability for plants, trees, and many crops. The results thus indicate that the net effect of climate change has made agricultural drought less likely and that the current severe impacts of drought on California's agriculture have not been substantially caused by long-term climate changes. [ABSTRACT FROM AUTHOR]

A study was conducted to compare the technical potential and effectiveness of different water supply options for securing water availability in a large-scale, interconnected water supply system under historical and climate-change augmented inflow and demand conditions. Part 2 of the study focused on determining the greenhouse gas and renewable energy utilization impacts of different pathways to stabilize major surface reservoir levels. Using a detailed electric grid model and taking into account impacts on the operation of the water supply infrastructure, the greenhouse gas emissions and effect on overall grid renewable penetration level was calculated for each water supply option portfolio that successfully secured water availability from Part 1. The effects on the energy signature of water supply infrastructure were found to be just as important as that of the fundamental processes for each option. Under historical (baseline) conditions, many option portfolios were capable of securing surface reservoir levels with a net neutral or negative effect on emissions and a benefit for renewable energy utilization. Under climate change augmented conditions, however, careful selection of the water supply option portfolio was required to prevent imposing major emissions increases for the system. Overall, this analysis provided quantitative insight into the tradeoffs associated with choosing different pathways for securing California's water supply. [ABSTRACT FROM AUTHOR]

The technical potential and effectiveness of different water supply options for securing water availability in a large-scale, interconnected water supply system under historical and climate-change augmented inflow and demand conditions were compared. Part 1 of the study focused on determining the scale of the options required to secure water availability and compared the effectiveness of different options. A spatially and temporally resolved model of California's major surface reservoirs was developed, and its sensitivity to urban water conservation, desalination, and water reuse was examined. Potential capacities of the different options were determined. Under historical (baseline) hydrology conditions, many individual options were found to be capable of securing water availability alone. Under climate change augment conditions, a portfolio approach was necessary. The water savings from many individual options other than desalination were insufficient in the latter, however, relying on seawater desalination alone requires extreme capacity installations which have energy, brine disposal, management, and cost implications. The importance of identifying and utilizing points of leverage in the system for choosing where to deploy different options is also demonstrated. [ABSTRACT FROM AUTHOR]

The article presents information about the Advanced Concepts Workshop on Remote Sensing of Precipitation at Multiple Scales that was held at the University of California, Irvine on March 15-17, 2010. Research priorities and recommendations from the participants are related to quantification of uncertainties about multisensor observations, improvements in precipitation retrieval algorithms, and development of metrics validation for research.

The article discusses the impact of California's drought, which began in 2012, on its forests, wildlife, and economy. Topics include the impact of growth in the state's population and agriculture on water use, California's adaptation to droughts through innovations such as water conservation, aqueduct networks, and water markets, and California's need for a proactive, long-term drought management plan that considers economical and environmental factors such as reduced precipitation or snow pack.

Natural disasters often affect the most vulnerable countries/communities around the world. However, within the same countries/communities, the impact of natural disasters is far greater on disadvantaged populations. We investigate how wildfires affect asthma prevalence in different populations across California. Our results indicate that although there is no discernible relationship between wildfires and asthma prevalence for California's population as a whole, wildfires and asthma prevalence in Black and senior populations have a strong relationship. We believe there is an urgent need to make high‐resolution health‐related data publicly available for in‐depth analyses of climate change impacts on society and disadvantage communities Key Points: The impact of natural disasters is greater on disadvantaged and vulnerable populations with respect to the overall populationThere is a need to make high‐resolution health‐related data publicly available for in‐depth analyses of climate change impacts on society [ABSTRACT FROM AUTHOR]

The article discusses drought in California as of March 28, 2014, suggesting that lessons can be learned from the Millennium Drought in Australia from 1997-2009. Topics include the economic impact of the Millennium Drought, the role of water reforms including water markets, irrigation infrastructure, and water entitlements to critical habitats and populations, and public reaction to drought.

The article notes the importance of satellite-based global precipitation measures and a forum at the University of California, Irvine which focused on remote sensing. Research priorities mentioned at the Advanced Concepts Workshop on Remote Sensing of Precipitation at Multiple Scales include improving satellite-based precipitation retrieval algorithms, developing validation metrics for research, and creating a near-real-time model of probabilistic uncertainty.

The article discusses the threat to California's levees as a result of a drought as of August 2015, noting problems such as soil organic carbon (SOC) decomposition, land subsidence, and future flooding risks in relation to similar situations in Australia, the Netherlands, and Texas.

In this study, we investigate the extent to which physical water resource availability constraints can limit the deployment of solar thermal and geothermal-based energy resources under future climate scenarios in California. This is accomplished by (1) calculating the water unconstrained potential capacity for solar thermal and geothermal power plants, (2) estimating the available water supply for supporting the water needs of these plants using four climate model simulations under representative concentration pathway (RCP) 8.5, and (3) determining the supportable capacity from the available water supply based on power plant cooling type. We show that regional water availability can limit the installable capacity of solar thermal resources to a range of 10.9–52.6% of solar thermal potential and geothermal resources to between 17.9% and 100% of geothermal potential, depending on cooling system and regional water demand levels by the year 2050. The limiting factor for installable capacity was driven by whether the locations of solar thermal and geothermal resources were spatially aligned with precipitation patterns, with cooling system type acting as a secondary factor. In regions with high solar thermal and geothermal potential, reducing water demand from other sectors was important for alleviating the water constraints on solar thermal and geothermal capacity and increasing total resource potential. Water conservation policies can therefore support the deployment of renewable energy resources and should be considered in future water and energy resource planning. [ABSTRACT FROM AUTHOR]

Highlights • Climate-induced variability in hydropower can increase greenhouse gas emissions. • Higher dispatchable capacity needed to compensate for hydropower variability. • Hydropower under climate change has minimal effects on renewable penetration. • Higher hydropower variability increases natural gas power plant start up events. • Climate-induced hydropower variability increases natural gas power plant downtime. Abstract This study investigates how hydropower generation under climate change affects the ability of the electric grid to integrate high wind and solar capacities. Using California as an example, water reservoir releases are modeled as a function of hydrologic conditions in the context of a highly-renewable electric grid in the year 2050. The system is perturbed using different climate models under the Representative Concentration Pathway 8.5 climate scenario. The findings reveal that climate change impact on hydropower can increase greenhouse gas emissions up to 8.1% due to increased spillage of reservoir inflow reducing hydropower generation, but with minimal effects (<1%) on renewable utilization and levelized cost of electricity. However, increases in dispatchable power plant capacity of +2.1 to +6.3% and decreases in the number of start-up events per power plant unit up to 3.1%, indicate that the majority of dispatchable natural gas power plant capacity is offline for most of the climate change scenarios. While system-wide performance metrics experience small impacts, climate change effects on hydropower generation increase both the need for dispatchable generation and the costs of electricity from these power plants to support large-scale wind and solar integration on the electric grid. [ABSTRACT FROM AUTHOR]