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Since 2006 the scientific community in California, in cooperation with resource managers, has been conducting periodic statewide studies about the potential impacts of climate change on natural and managed systems. This Special Issue is a compilation of revised papers that originate from the most recent assessment that concluded in 2009. As with the 2006 studies that influenced the passage of California's landmark Global Warming Solutions Act (AB32), these papers have informed policy formulation at the state level, helping bring climate adaptation as a complementary measure to mitigation. We provide here a brief introduction to the papers included in this Special Issue focusing on how they are coordinated and support each other. We describe the common set of downscaled climate and sea-level rise scenarios used in this assessment that came from six different global climate models (GCMs) run under two greenhouse gas emissions scenarios: B1 (low emissions) and A2 (a medium-high emissions). Recommendations for future state assessments, some of which are being implemented in an on-going new assessment that will be completed in 2012, are offered. [ABSTRACT FROM AUTHOR]

Climate change will affect the demand of many resources that households consume, including electricity and natural gas. Although price is considered an effective tool for controlling demand for many resources that households consume, including electricity and natural gas, there is disagreement about the exact magnitude of the price elasticity. Part of the problem is that demand is confounded by block pricing and the interrelated consumption of electricity and natural gas, which prevent easy estimation of price impacts. Block pricing suggests that the purchaser controls the marginal price of a commodity by the quantity purchased, turning price into an endogenous variable. Interrelated consumption indicates that demand for one resource is affected by the price of another. These complications have made difficult the estimation of the price elasticity of demand for resources and consequently the household-level impact of climate change, which will affect resource supplies. This paper evaluates statistical tools for estimating the joint demand for natural gas and electricity when both resources face a block price setting and develops estimates of own and cross price elasticity. We use data from the Federal Residential Energy Consumption Survey, along with utility price data, to estimate the household demand for electricity and natural gas in California as separate commodities. We then use a joint estimation procedure to evaluate the household demand for natural gas and electricity. Finally, we evaluate the degree to which block pricing and interrelated demand affect the price elasticity of demand for the two resources. The paper ends by noting the continuing uncertainty surrounding the use of price to manage household demand for electricity and natural gas. [ABSTRACT FROM AUTHOR]

This paper explores what the San Diego region may look like in the year 2050 as projected changes in regional climate conditions take place. Focusing on interrelated issues of climate change, sea level rise, population growth, land use, and changes in water, energy, public health, wildfires, biodiversity, and habitat, the paper reviews the potential impacts of a changing climate by 2050 and makes recommendations for changes in planning processes at the local and regional levels to prepare for these impacts. The original research for this study was completed in 2008 by a team of 40 experts from the region including universities, nonprofit organizations, local governments, public sector agencies and private sector entities. This paper has now been updated with more recent research regarding climate change adaptation while preserving the integrity of the original research team's work. The simulated impacts discussed in this study are based on regional projections of climate change generated by scientists at Scripps Institution of Oceanography, employing three climate models and two emissions scenarios used by the Intergovernmental Panel on Climate Change. The impacts are discussed in the context of significant regional growth expected during the period as well as an aging population base. Key issues explored in the report include potential inundation of six selected low-lying coastal areas in San Diego due to sea level rise, potential shortfalls in water deliveries, peak energy demand increases due to higher temperatures, growing risk of devastating wildfires, migrations of species in response to higher temperatures in an increasingly fragmented natural habitat, and public health issues associated with extreme temperature events. [ABSTRACT FROM AUTHOR]

In this paper we propose a framework for evaluating how prepared California resource managers are for risks of continued climate change. The framework presented suggests three critical dimensions of preparedness - awareness of climate-related risks, analytic capacity to translate such climate risks information into specific planning and management activities, and the extent of actions taken to address the risks. We illustrate the application of this framework in this paper through preliminary research of California coastal managers where we identify limited awareness of climate-change related risks, limited analytic capacity, and significant constraints on the abilities of institutions and individuals to take adaptation actions. Our analysis suggests that for California to realize its significant adaptive capacity and be able to manage the unavoidable impacts of climate change, resource managers need to be engaged more effectively in future discussions of managing climate risks in the state. [ABSTRACT FROM AUTHOR]

Over the last few years, California has passed some of the strongest climate policies in the USA. These new policies have been motivated in part by increasing concerns over the risk of climate-related impacts and facilitated by the state's existing framework of energy and air quality policies. This paper presents an overview of the evolution of this increased awareness of climate change issues by policy makers brought about by the strong link between climate science and policy in the state. The State Legislature initiated this link in 1988 with the mandate to prepare an assessment of the potential consequences of climate change to California. Further interactions between science and policy has more recently resulted, in summer of 2006, in the passage of Assembly Bill 32, a law that limits future greenhouse gas emissions in California. This paper discusses the important role played by a series of state and regional climate assessments beginning in 1988 and, in particular, the lessons learned from a recently completed study known as the Scenarios Project. [ABSTRACT FROM AUTHOR]

Increasing global temperatures are likely to have major impacts on agriculture, but the effects will vary by crop and location. This paper describes the temperature sensitivity and exposure of selected specialty crops in California. We used literature synthesis to create several sensitivity indices (from 1 to 4) to changes in winter minimum and summer maximum temperature for the top 14 specialty crops. To estimate exposure, we used seasonal period change analysis of mid-century minimum and maximum temperature changes downscaled to county level from CMIP5 models. We described crop vulnerability on a county basis as (crop sensitivity index × county climate exposure × area of crop in county); individual crop vulnerabilities were combined to create an aggregate index of specialty crop vulnerability by county. We also conducted analyses scaled by crop value rather than area, and normalized to total specialty crop area in each county. Our analyses yielded a spatial assessment highlighting seasons and counties of highest vulnerability. Winter and summer vulnerability are correlated, but not highly so. High-producing counties (e.g., Fresno County in the San Joaquin Valley) are the most vulnerable in absolute terms, while northern Sacramento Valley counties are the most vulnerable in relative terms, due to their reliance on heat-sensitive perennial crops. Our results illustrate the importance of examining crop vulnerability from different angles. More physiological and economic research is needed to build a comprehensive picture of specialty crop vulnerability to climate change. [ABSTRACT FROM AUTHOR]

Downscaled climate change projections for California, when translated into changes in irrigation water delivery and then into profit from agriculture in the Central Valley, show an increase in conventional measures of variability such as the variance. However, these increases are modest and mask a more pronounced increase in downside risk, defined as the probability of unfavorable outcomes of water supply or profit. This paper describes the concept of downside risk and measures it as it applies to outcomes for Central Valley agriculture projected under four climate change scenarios. We compare the effect of downside risk aversion versus conventional risk aversion or risk neutrality when assessing the impact of climate change on the profitability of Central Valley agriculture. We find that, when downside risk is considered, the assessment of losses due to climate change increases substantially. [ABSTRACT FROM AUTHOR]

This paper is among the first to report on the full integration of basin-scale models that include projections of the demand and supply of water and energy for residential, commercial, industrial, and agricultural sector users. We link two widely used regional planning models that allow one to study the impact of rising climate variability on water and electricity use in Sacramento, California. Historic data combined with the current energy and water system configuration was used to assess the implications of changes in temperature and precipitation. Climate simulations suggest that electricity imports to the region would increase during hot dry spells, when regional power production is most constrained. In particular, regional imports of electricity would increase over 35 % in hot dry years, assuming a 4 °C increase in average temperature and a 25 % decrease in average precipitation. [ABSTRACT FROM AUTHOR]

Exploiting surface albedo change has been proposed as a form of geoengineering to reduce the heating effect of anthropogenic increases in greenhouse gases (GHGs). Recent modeling experiments have projected significant negative radiative forcing from large-scale implementation of albedo reduction technologies ('cool' roofs and pavements). This paper complements such model studies with measurement-based calculations of the direct radiation balance impacts of replacement of conventional roofing with 'cool' roof materials in California. This analysis uses, as a case study, the required changes to commercial buildings embodied in California's building energy efficiency regulations, representing a total of 4300 ha of roof area distributed over 16 climate zones. The estimated statewide mean radiative forcing per 0.01 increase in albedo (here labeled RF01) is −1.38 W/m. The resulting unit-roof-area mean annual radiative forcing impact of this regulation is −44.2 W/m. This forcing is computed to counteract the positive radiative forcing of ambient atmospheric CO at a rate of about 41 kg for each square meter of roof. Aggregated over the 4300 ha of cool roof estimated built in the first decade after adoption of the State regulation, this is comparable to removing about 1.76 million metric tons (MMT) of CO from the atmosphere. The point radiation data used in this study also provide perspective on the spatial variability of cool roof radiative forcing in California, with individual climate zone effectiveness ranging from −37 to −59 W/m of roof. These 'bottom-up' calculations validate the estimates reported for published 'top down' modeling, highlight the large spatial diversity of the effects of albedo change within even a limited geographical area, and offer a potential methodology for regulatory agencies to account for the climate effects of 'cool' roofing in addition to its well-known energy efficiency benefits. [ABSTRACT FROM AUTHOR]

Climate change is likely to pose considerable new challenges to California's electricity sector. This paper primarily focuses on the adaptation challenges of an important component of the energy arena: electricity demand in the residential and commercial sectors and electricity supply. The primary challenge to California's electricity sector will likely be the increase in demand for air conditioning as a result of rising temperatures. In addition, renewable energy sources, which are an increasing share of the electricity portfolio, are particularly vulnerable to climate change. Many of the key players have been actively considering the implications of climate change. Because electricity generation accounts for nearly 30% of greenhouse gas emissions, this sector has been a target of the state's efforts to reduce emissions. Fortunately, many of the same tools can simultaneously improve the sector's resilience to a changing climate. Demand management strategies and supply diversification are both important strategies. Local governments can play a central role in encouraging the adoption of more energy efficient building codes and the use of more renewable sources, such as solar energy. The positive steps taken by many local governments are encouraging. Steps to increase public awareness are an important, often missing component, however. Increases in research, development, and demonstration to improve system resiliency and develop new energy conservation tools are also needed. [ABSTRACT FROM AUTHOR]

California is home to some of the worst air quality in the nation and ninety percent of the state's population lives in areas that are out of attainment with at least one of the National Ambient Air Quality Standards. Increasing temperatures associated with climate change will make meeting air quality standards more difficult. Under a changing climate, additional emission reductions will be needed to achieve clean air standards. These additional emission reductions and associated costs are called the 'climate penalty.' Air quality planning is the process of assessing the emission reductions needed to meet air quality standards and outlining the programs and policies that will be implemented to achieve these emission reductions. This paper reviews the challenges that a changing climate will pose for air quality planning in California and identifies opportunities for adaptation. While state air quality regulators in California are taking enormous strides to address global warming, less work is happening at the regional, air district level. Air districts are the agencies responsible for developing air quality improvement plans. An important first step for regional air quality regulators will be to quantify the climate penalty and understand their region's vulnerability to climate change. Limitations in regulatory authority could impede measures to improve preparedness. Regional agencies will likely need to look to state and federal agencies for additional emission reductions. [ABSTRACT FROM AUTHOR]

This paper explores concepts of carbon lock-in arising from the technologies of CO capture and storage (CCS). We examine the argument that CCS reduces carbon lock-in and the calls for a CCS 'mandate' and emission performance standards. We analyse the pros- and cons- of a low-carbon fossil fuel lock-in, arguing that lock-in per se is not the problem; it is rather the depth of lock-in which creates problems because deeper lock-in reduces flexibility and increases the 'error cost' (i.e. the cost of a decision which turns out to be based on incorrect understanding) and should be avoided. A set of technical and institutional indicators for measuring the flexibility of different technologies is then presented and applied to three technologies: a landfill gas power generator, a conventional nuclear power plant and a CCS plant under development in California. We conclude that these indicators are a useful way forward in assessing individual projects and that public authorities and other stakeholders might wish to employ some version of these indicators in their deliberations on the role of CCS. [ABSTRACT FROM AUTHOR]

This paper describes research to estimate the effects of climate change on two high-elevation hydropower systems in California: the Upper American River Project, operated by the Sacramento Municipal Utility District, and the Big Creek system, operated by Southern California Edison. The study builds on a previous model of the Upper American River Project, which is here modified and extended for use to simulate two hydropower systems under various conditions. Future operations of the two high-elevation systems are simulated using climate change scenarios provided for the Second California Assessment. These scenarios suggest reduced precipitation and reduced runoff for both systems, and a shift toward runoff earlier in the year. The change in the hydrograph is somewhat greater for the Upper American River Project system, because its basins lie at a lower elevation. Reduced runoff directly reduces energy generation and revenues from both systems. Because the Upper American River Project system is projected to have greater spills with warmer climate conditions, it also has greater reduction in energy generation and revenues. Both systems continue to meet peak historical power demands in summer under most climate projections. However, if the number of heat waves increases in the late summer (September), reservoir operating strategies may need to be modified. [ABSTRACT FROM AUTHOR]

This paper explores the independent and combined effects of changes in temperature and runoff volume on California's water supply and potential water management adaptations. Least-cost water supply system adaptation is explored for two climate scenarios: 1) warmer-drier conditions, and 2) warmer conditions without change in total runoff, using the CALVIN economic-engineering optimization model of California's intertied water supply system for 2050 water demands. The warm-dry hydrology was developed from downscaled effects of the GFDL CM2.1 (A2 emissions scenario) global climate model for a 30-year period centered at 2085. The warm-only scenario was developed from the warm-dry hydrology, preserving its seasonal runoff shift while maintaining mean annual flows from the historical hydrology. This separates the runoff volume and temperature effects of climate change on water availability and management adaptations. A warmer climate alone reduces water deliveries and increases costs, but much less than a warmer-drier climate, if the water supply system is well managed. Climate changes result in major changes in reservoir operations, cyclic storage of groundwater, and hydropower operations. [ABSTRACT FROM AUTHOR]

California is likely to experience increased coastal flooding and erosion caused by sea-level rise over the next century, affecting the state's population, infrastructure, and environment. As part of a set of studies on climate change impacts to California, this paper analyzes the potential impacts from projected sea-level rise if no actions are taken to protect the coast (a 'no-adaptation scenario'), focusing on impacts to the state's population and infrastructure. also covered effects on wetlands, costs of coastal defenses, and social and environmental justice related to sea-level rise. We analyzed the effect of a medium-high greenhouse gas emissions scenario (Special Report on Emissions Scenarios A2 in IPCC ) and included updated projections of sea-level rise based on work by Rahmstorf (Science 315(5810): 368, ). Under this scenario, sea levels rise by 1.4 m by the year 2100, far exceeding historical observed water level increases. By the end of this century, coastal flooding would, under this scenario, threaten regions that currently are home to approximately 480,000 people and $100 billion worth of property. Among those especially vulnerable are large numbers of low-income people and communities of color. A wide range of critical infrastructure, such as roads, hospitals, schools, emergency facilities, wastewater treatment plants, and power plants will also be at risk. Sea-level rise will inevitably change the character of California's coast; practices and policies should be put in place to mitigate the potentially costly and life-threatening impacts of sea-level rise. [ABSTRACT FROM AUTHOR]

In this paper we study an isolated high-mountain (Sierra Nevada, SE Iberian Peninsula) to identify the potential trends in the habitat-suitability of five key species (i.e. species that domain a given vegetation type and drive the conditions for appearance of many other species) corresponding to four vegetation types occupying different altitudinal belts, that might result from a sudden climatic shift. We used topographical variables and downscaled climate warming simulations to build a high-resolution spatial database (10 m) according to four different climate warming scenarios for the twenty-first century. The spatial changes in the suitable habitat were simulated using a species distribution model, in order to analyze altitudinal shifts and potential habitat loss of the key species. Thus, the advance and receding fronts of known occurrence locations were computed by introducing a new concept named differential suitability, and potential patterns of substitution among the key species were established. The average mean temperature trend show an increase of 4.8°C, which will induce the vertical shift of the suitable habitat for all the five key species considered at an average rate of 11.57 m/year. According to the simulations, the suitable habitat for the key species inhabiting the summit area, where most of the endemic and/or rare species are located, may disappear before the middle of the century. The other key species considered show moderate to drastic suitable habitat loss depending on the considered scenario. Climate warming should provoke a strong substitution dynamics between species, increasing spatial competition between both of them. In this study, we introduce the application of differential suitability concept into the analysis of potential impact of climate change, forest management and environmental monitoring, and discuss the limitations and uncertainties of these simulations. [ABSTRACT FROM AUTHOR]

This paper provides both a detailed history of environmental change in the Sierra Nevada over the past 1,800 years and evidence for climate teleconnections between the Sierra Nevada and Greenland during the late Holocene. A review of Greenland ice core data suggests that the magnitudes of abrupt changes in temperature and precipitation increased beginning c. 3,700 and 3,000 years ago, respectively. Precipitation increased abruptly 1,300 years ago. Comparing paleotemperature data from Cirque Peak, CA with paleoprecipitation data from Pyramid Lake, NV suggests that hot temperatures occurred at the beginnings of most severe droughts in the Sierra Nevada over the past 1,800 years. Severe fires and erosion also occurred at Coburn Lake, CA at the beginning of all severe droughts in the Sierra Nevada over the past 1,800 years. This suggests that abrupt climate change during the late Holocene caused vegetation and mountain slopes in some areas to be out of equilibrium with abruptly changed climates. Finally, the ending of drought conditions in Greenland coincided with the beginning of drought conditions in the Sierra Nevada over the past 1,800 years, perhaps as a result of the rapidly changed locations of the Earth's major precipitation belts during abrupt climate change events. [ABSTRACT FROM AUTHOR]

This paper presents results from a 40 year Weather Research and Forecasting (WRF) based dynamical downscaling experiment performed at 12 km horizontal grid spacing, centered on the state of California, and forced by a 1° × 1.25° finite-volume current-climate Community Climate System Model ver. 3 (CCSM3) simulation. In-depth comparisons between modeled and observed regional-average precipitation, 2 m temperature, and snowpack are performed. The regional model reproduces the spatial distribution of precipitation quite well, but substantially overestimates rainfall along windward slopes. This is due to strong overprediction of precipitation intensity; precipitation frequency is actually underpredicted by the model. Moisture fluxes impinging on the coast seem to be well-represented over California, implying that precipitation bias is caused by processes internal to WRF. Positive-definite moisture advection and use of the Grell cumulus parameterization result in some decrease in precipitation bias, but other sources are needed to explain the full bias magnitude. Surface temperature is well simulated in all seasons except summer, when overly-dry soil moisture results in a several degree warm bias in both CCSM3 and WRF. Additionally, coastal temperatures appear to be too warm due to a coastal sea surface temperature bias inherited from CCSM3. Modeled snowfall/snowmelt agrees quite well with observations, but snow water equivalent is found to be much too low due to monthly reinitialization of all regional model fields from CCSM3 values. [ABSTRACT FROM AUTHOR]

In addition to reducing greenhouse gas emissions, actions to achieve a sustainable coexistence with wildfire need to be taken now. In this paper we suggest several important policy, planning, and management changes that should be made, regardless of the many uncertainties in predicting future fire regimes. Similar to how other natural hazards are addressed, a risk-based framework for fire-related decisions is crucial. Reintroduction of fire to fire-prone ecosystems, careful use of fire surrogates, and creation of new and flexible policies will be needed for successful ecosystem management. Growing incompatibilities between urban development and wildfire also require a serious reevaluation of urban planning and building in fire-prone locations to reach a sustainable coexistence with fire. Our future cities and communities must be less susceptible to wildfire damage, and the ecosystems upon which we depend must be made more resilient to further disruptions in fire regimes. [ABSTRACT FROM AUTHOR]

Species of plants and animals have characteristic climatic requirements for growth, survival and reproduction that limit their geographic distribution, abundance and interactions with other species. To analyze this complexity requires the development of models that include not only the effects of biotic factors on species dynamics and interactions, but also the effects of abiotic factors including weather. The need for such capacity has appreciably increased as we face the threat of global climate change. In this paper, bi- and tri-trophic physiologically based demographic models of alfalfa, cotton, grape, olive and the noxious weed yellow starthistle systems are used to explore some of the potential effects of climate change. A general model that applies to all species in all trophic levels (including the economic one) is used to simulate the effects of observed and projected weather on system dynamics. Observed daily weather and that of climate model scenarios were used as forcing variables in our studies. Geographic information system (GRASS GIS) is used to map the predicted effects on species across the varied ecological zones of California. The predictions of the geographic distribution and abundance of the various species examined accords well with field observations. Furthermore, the models predict how the geographic range and abundance of the some species would be affected by climate change. Among the findings are: (1) The geographic range of tree species such as olive that require chilling to break dormancy (i.e. vernalization) may be limited in some areas due to climate warming, but their range may expand in others. For example, olive phenology and yield will be affected in the southern part of California due to high temperature, but may expand in northern areas until limited by low winter temperatures. Pest distribution and abundance will also be affected. For example, climate warming would allow the cold intolerant pink bollworm in cotton to expand its range into formerly inhospitable heavy frost areas of the San Joaquin Valley, and damage rates will increase throughout its current range. The distribution and abundance of other cold intolerant pests such as olive fly, the Mediterranean fruit fly and others could be similarly affected. In addition, species dominance and existence in food webs could change (e.g. in alfalfa), and the biological control of invasive species might be adversely affected (e.g. vine mealybug in grape). The distribution and abundance of invasive weeds such as yellow starthistle will be altered, and its control by extant and new biological control agents will be difficult to predict because climate change will differentially affects each. (2) Marginal analysis of multiple regression models of the simulation data provides a useful way of analyzing the efficacy of biological control agents. Models could be useful as guides in future biological control efforts on extant and new exotic pest species. (3) Major deficiencies in our capacity to predict the effects of climate change on biological interactions were identified: (1) There is need to improve existing models to better forecast the effects of climate change on crop system components; (2) The current system for collecting daily weather data consists of a patchwork of station of varying reliability that often record different variables and in different units. Especially vexing, is the dearth of solar radiation data at many locations. This was an unexpected finding as solar energy is an important driving variable in biological systems. [ABSTRACT FROM AUTHOR]

This paper presents preliminary efforts by agencies managing California's water resources to incorporate climate change research into their planning and management tools. Projected increases in air temperature may lead to changes in the precipitation patterns, runoff timing and volume, sea level rise, and changes in the amount of irrigation water needed due to modified evapotranspiration rates. Historical observations of climate change related to California's water resources are shown. Results from preliminary modeling studies of potential impacts of climate change to operations of the State Water Project and Central Valley Project, Delta water quality and water levels, flood forecasting and evapotranspiration rates are presented. Future directions to incorporate risk assessment are discussed. [ABSTRACT FROM AUTHOR]

Economically optimal operational changes and adaptations for California's water supply system are examined for a dry form of climate warming (GFDL CM2.1 A2) with year 2050 water demands and land use. Economically adaptive water management for this climate scenario is compared to a similar scenario with the historical climate. The effects of population growth and land use alone are developed for comparison. Compared with the historic hydrology, optimized operations for the dry climate warming scenario raise water scarcity and total operation costs by $490 million/year with year 2050 demands. Actual costs might be somewhat higher where non-economic objectives prevail in water management. The paper examines the economical mix of adaptation, technologies, policies, and operational changes available to keep water supply impacts to such modest levels. Results from this screening model suggest promising alternatives and likely responses and impacts. Optimized operations of ground and surface water storage change significantly with climate. Dry-warm climate change increases the seasonal storage range of surface reservoirs and aquifers. Surface reservoir peak storage usually occurs about a month earlier under dry-warm climate change. [ABSTRACT FROM AUTHOR]

Potential global climate change impacts on hydrology pose a threat to water resources systems throughout the world. The California water system is especially vulnerable to global warming due to its dependence on mountain snow accumulation and the snowmelt process. Since 1983, more than 60 studies have investigated climate change impacts on hydrology and water resources in California. These studies can be categorized in three major fields: (1) Studies of historical trends of streamflow and snowpack in order to determine if there is any evidence of climate change in the geophysical record; (2) Studies of potential future predicted effects of climate change on streamflow and; (3) Studies that use those predicted changes in natural runoff to determine their economic, ecologic, or institutional impacts. In this paper we review these studies with an emphasis on methodological procedures. We provide for each category of studies a summary of significant conclusions and potential areas for future work. [ABSTRACT FROM AUTHOR]