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Public Interest Energy Research Program: Final Project Report

cover of report Climate Change and Health In California
A PIER Research Roadmap

Publication Number: CEC-500-2005-093
Publication Date: May 2005
PIER Program Area: Energy-Related Environmental Research

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Executive Summary

This roadmap assesses the potential health impacts of global warming on California and covers both direct and indirect effects on human health, to identify research gaps and needs, and to determine priority areas to be addressed for disease prevention.

Global warming is not uniform and is subject to regional variations. California enjoys seven climate regions ranging from the hot, arid desert to cool, rainy forests. Global warming is expected to affect California via temperature and sea level rise, as well as through altered timing of annual precipitation, with extreme weather events more likely to become more intense and frequent. Subsequent health effects will likely include: heat-related and wildfire-related morbidity and mortality; casualties from extreme weather events; changed air pollution and allergen exposure; infectious diseases (particularly vectorborne and waterborne microbes); and other climate-related issues such as the effects on food productivity and safety.

Heat Waves

Increased heat waves due to climate change would cause more heat-related illnesses and deaths. Nationally, heat waves are more deadly natural disasters than hurricanes, flooding, or tornadoes. California was one of the states in the western region that showed the most extreme rise in frequency of high heat stress events and heat waves from 1949 to 1995. The U.S. Environmental Protection Agency (EPA) estimates that a 3°F warming could almost double the heat-related deaths in Los Angeles, from 70 (in 1997) to 125 (although increased air conditioning use may not have been fully accounted for). Little change in winter mortality is expected. The heat-related mortality in Los Angeles for example, would increase by 62% to 88% of current levels under global climate model (GCM) scenarios, assuming full acclimation.

Research Needs

Research needs on health effects of heat waves in California are quite similar to those identified nationally by the U.S. National Assessment, and include:

  • Determining which weather parameters contribute most to morbidity and mortality, thereby improving predictions and early warning potential. For example, determining which of the current heat indices and/or synoptic air mass classifications best predict adverse health outcomes.

  • Analyzing urban characteristics that are responsible for inter-city variability in heat vulnerability. These characteristics may be geographic, or related to house type or factors associated with the urban heat island effect. Research should identify whether temperature thresholds are variable across California cities.

  • Conducting additional studies focused on the association between heat and morbidity (as well as mortality).

  • Evaluating the feasibility and effectiveness of specialized health education efforts aimed at reaching susceptible populations.

  • Standardized reporting of heat-related mortality is lacking and requires attention. Diagnostic guidelines and criteria for use by medical examiners should be adopted.

  • Assessing net annual health impacts, comparing both summer and winter mortality projections under climate change scenarios.

  • Evaluating the effectiveness of current warning systems.

  • Determining whether a threshold temperature exists, above which Californians may suffer adversely.


Wildfires are common in the hills throughout California and in the coastal communities of Southern California. Fire has always been a trait of the area’s chaparral and grassland ecosystems, as well as in other parts of California’s complex landscape. The largest fires in southern California have historically occurred in the autumn, when Santa Ana winds can develop with high temperatures (conditions are characterized by low relative humidity, high temperatures, and strong northeasterly winds). Modeling results showed that the most severe effects of global climate change would occur in the Sierra foothills where the predicted number of potentially catastrophic fires increased by 143% in grassland and 121% in chaparral. Conditions that are more conducive to fires can occur with hotter and drier summers and greater amount of vegetation resulting from wetter winters. Plant pests and pathogens can also raise the risk of fire by increasing the number of dead trees in an area.

Research Needs

  • Because wildfires can have serious consequences for health, further research is needed to assess wildfire risks under a changed climate; particularly the effect of climate change on Santa Ana winds, winter precipitation, and peak summer temperatures.

  • Study the effect of climate change on plant pest infestation.

  • Smoke from wildfires can affect air quality. With more fires likely under a changed climate, the contribution of fires to health effects from compromised air quality for Californians would be an important area for further research.

  • More studies are needed on morbidity from woodland fires.

Extreme Events

According to the National Aeronautics and Space Administration (NASA), extreme events rose from 0.1% of wet days per year to 1% for the decade 2040–2049, modeled under climatic change. Such is the projection for all major basins in California. By the year 2100, temperatures in California could rise by about 5°F, precipitation could increase by 20%–30%, and sea level could rise 13 to 19 inches if warming goes unchecked, according to the EPA and the Intergovernmental Panel on Climate Change (IPCC).

Wet weather is one of the root causes of landslides. California has certain land forms that are especially susceptible to landslides—most visibly the coastal bluffs and mountains. In some cases, human-caused fires, erosion, and vegetation changes make landslides more likely to occur.

Research Needs

  • Improved downscaling of global climate models (GCMs) of future climate change, to reach temporal and spatial scales useful for projecting trends in regional extreme events.

  • Post-disaster disease surveillance and studies on long-term health effects such as Post Traumatic Stress Disorder (PTSD). Databases should utilize standardized definitions and outputs. To fully understand climate-driven health impacts, we need long time-series of compatible data from integrated monitoring programs.

  • Analyses on non–climate risk factors—such as geographical topography, stream flow velocities, and coastal/floodplain development—that modify the impact of storms. Valuation of current urban and rural development practices on risk is needed—specifically, the effects of altered land use on vulnerability to extreme weather.

  • Flow studies are needed that delineate toxic releases into water supplies, and their potential health effects. Geographic Information Systems (GIS) analyses should include toxics and population densities in flood plains.

  • Epidemiologic studies of the public health effects of flooding.

Air Quality

Climate change may affect exposure to air pollutants by affecting weather, anthropogenic emissions, and biogenic emissions—and by changing the distribution and types of airborne allergens. Local temperature, precipitation, clouds, atmospheric water vapor, wind speed, and wind direction influence atmospheric chemical processes, and interactions occur between local and global-scale environments.

Parts of California already have bad air quality, and most counties have higher smog levels than acceptable by California regulatory agencies. The nation’s four smoggiest urban areas are all in California. Six metropolitan areas in the state are listed as having the 10 highest-ozone levels in the nation, which makes California the smoggiest state in the nation, with Southern California being the worst off. Tropospheric ozone (smog) is already a critical problem in California. The Los Angeles South Coast Air Basin is the only area in the country given an "extreme" rating for ozone concentration by the EPA.

Higher temperatures increase ozone formation at ground level when precursors and sunlight are present. If wetter conditions increase biomass, which emits ozone precursors, then air quality could deteriorate. Ozone and non-volatile secondary particulate matter (PM) will generally increase at higher temperature, due to an increased gas-phase reaction rate. Other climate/air pollution health risks involve transboundary dust, persistent pollutants, and fungal spores.

Research Needs

  • Improved air pollution models in general and their linkage with climate change, including combined effects of temperature and humidity on air pollution.

  • Analyses that address the association between weather and all hazardous pollutants. Most is known about the link between ozone and temperature, but even for ozone, improved modeling of stagnant air masses and emissions scenarios is needed.

  • Better understanding of boundary layer dynamics.

  • Climate effects on fine particulates.

  • Emission scenarios that include primary and secondary pollutants stemming from altered energy demand, as well as vegetative sources.

  • The interaction of ozone and direct heat effects on mortality is difficult to disentangle, but important for better prioritizing interventions during heat waves.

  • Assessment of the risks of transboundary dust, as well as ozone precursors, is needed.

  • More must be known about climate effects on allergens (via temperature, carbon dioxide (CO2), or altered growing season) and soil fungi, such as that causing coccidioidomycosis; as well as about mold exposure following flooding.

  • Closing gaps in the understanding of exposure patterns and health effects

  • Address the balance between heavy precipitation (as a tropospheric "cleansing" mechanism) versus heat-related or stagnant air mass exacerbation of pollution.

  • Determine if a link exists between stratospheric ozone and climate change and whether this link could affect the speed of ozone hole recovery.

  • Assess health risks that result from the use of technological adaptations that can increase air pollution (e.g., air conditioner use). Also, if new pesticides are used as an insect control measure, assess the effects of these pesticides on human health.

Infectious Vectorborne Diseases

Western equine encephalitis (WEE) increases in cool, wet, El Niño years; whereas, St. Louis encephalitis (SLE) does so in hot, dry, La Niña years. Both WEE and SLE are caused by arboviruses. The activity of these viruses has increased in California over the last decade. Research shows a positive correlation between increased winter precipitation (or spring snow accumulation) and summer abundance of Culex tarsalis—a mosquito that carries the viruses that cause these diseases—meaning that prior season moisture indices may be useful predictors of summer mosquito abundance. A 3°C–5°C (5°F–9°F) increase in average temperature may cause a northern shift in the distribution of both WEE and SLE outbreaks and a decreased range of WEE in Southern California, based on temperature sensitivity of both virus and mosquito carrier. Other climate-sensitive vectorborne diseases that occur in California are: West Nile virus, malaria, tickborne diseases, plague, and hantavirus.

Research Needs

  • Improvement of surveillance systems for the arthropod vector and vertebrate hosts involved in the pathogen maintenance/transmission cycles, to allow for more accurate predictive capability for epidemic/epizootic transmission. New approaches to monitoring, such as frequent and long-term sampling to monitor the full range of specific vector species, are necessary in order to provide convincing direct evidence of climate change effects.

  • Improvement of active laboratory-based disease surveillance and prevention systems at the state and local level.

  • System-modeling of transmission risk under future climate scenarios.

  • Determination of predictable climate patterns that may provide early warning systems (e.g., the El Niño Southern Oscillation, or ENSO).

  • Studies of transmission dynamics (including reservoir host and vector ecology).

  • Analysis of habitat change and its effect on disease vectors and intermediate hosts.

  • Improvement of rapid diagnostic tests for pathogens.

  • More effective and rapid electronic exchange of surveillance data.

  • Further research is needed on specific conditions that may result in outbreaks of infectious diseases such as cocci and West Nile virus. Looking into quantitative analysis of incidence data in conjunction with time-series climate data is an example.

  • To better examine the relationship that exists between climatic variability and Hantavirus Pulmonary Syndrome (HPS) incidence, it may be necessary to analyze factors (e.g., temperature, precipitation, elevation, vegetation density) that may influence fluctuations in rodent populations. Weather monitoring stations, global positioning systems, vegetation surveys—as well as satellite-based remote sensors— can be used as tools for data collection.

  • Reassess the appropriate levels of evidence, including dealing with the uncertainties attached to detecting the health impacts of global change. Only limited databases are available to address the health impacts of extreme climate variability and change. Much of the information comes from epidemic investigations in which researchers focus their attention on a single event and gather data for only a short period.

  • A concerted effort to acquire more complete, long-term data sets is essential. Resolving the many questions about associations among weather, climate, and disease requires: (1) the identification of model systems or diseases that allows the development of long-term, high-quality data sets, and (2) sustained funding to make this research possible.

Infectious Waterborne Diseases

California’s sewage and wastewater treatment systems are already overloaded and overflow with heavy rainfall. These discharges may increase as winter storms increase in frequency and intensity. Also, in Southern California, rising sea level will exacerbate saltwater intrusion into freshwater aquifers and impact the quality of surface water supplies. Data on drinking water outbreaks in the United States from 1948 to 1994 (from all infectious agents) demonstrated a distinct seasonality, a spatial clustering in key watersheds, and a statistical association with extreme precipitation. In California, HIV-infected persons and other immunocompromised individuals (e.g., cancer patients) are at high risk for serious illness or fatality from cryptosporidiosis.

Research Needs

For California, research needs are parallel with national needs, and include:

  • Assessment of land use effects on water quality, through better assessment at the watershed level of the transport and fate of microbial pollutants associated with rain and snowmelt.

  • Determination of high risk watersheds prone to threaten water quality under conditions of extreme climate variability.

  • Studies addressing agricultural watershed protection (e.g., forested buffers) to reduce contaminated runoff from livestock operations.

  • Assessment of links between altered runoff (e.g., earlier snowmelt) and water availability and quality.

  • Improved surveillance and prevention of waterborne disease outbreaks, including better spatial and temporal resolution of reporting.

  • Epidemiologic studies that quantify the risks associated with multiple etiologic agents.

  • Molecular tracing of waterborne pathogens for accurate source identification.

  • Links between drinking water, recreational exposure, and food-borne disease monitoring.

  • Analysis of precipitation, streamflow, and risk from contamination of beaches during recreational use.

  • Links between marine ecology and toxic algae.

  • Vulnerability assessment and improved water and wastewater treatment systems.

  • Event monitoring, and development and implementation of better monitoring tools for waterborne microorganisms.

  • Vulnerability assessments of communities and ecosystems with respect to the effects of impaired wastewater management.

  • Wastewater management also can be improved. Although most large urban centers have well-developed systems to transport, treat, and discharge wastewaters, these systems are aging and becoming overburdened by increasing population. Weather perturbations, such as increased precipitation, can increase the load to combined sewer systems and sanitary sewers through increased inflow and infiltration. To effectively treat wastewater under these conditions, facilities must increase their capacity and storage and improve their process control. Research is needed to better assess the effect of increased runoff and the capacity of these water systems to prevent contamination. Assessment of the impacts of subsurface disposal on ground water and surface microbial water quality is needed for appropriate decisions to be made regarding non-point sources for popular tourist areas and coastal communities.

  • Watershed protection will continue to be an extremely important factor influencing water quality. Watershed water quality directly affects source water and finished water quality, as well as recreational sites and coastal waters. Better farming practices (to capture and treat agricultural wastes) and surrounding vegetation buffers, along with improved city disposal systems to capture and treat wastes, would reduce the runoff of nutrients, toxic chemicals, trace elements, and microorganisms flowing into reservoirs, ground water, lakes, rivers, estuaries, and coastal zones. For urban watersheds, more than 60% of the annual load of contaminant is transported during storm events. Advances in research and monitoring tied to hydrologic quantity and quality models are needed to improve the assessment and the changes that are needed in watersheds to protect water quality for downstream users and ecosystems.

Other Infectious Agents

Increased aridity and eventual desertification from increasing temperatures may increase the potential for coccidioidomycosis (cocci). The spores of the Coccidioides immitis fungus is spread by dust, often preceded by increased rain. A well-documented cocci outbreak followed the 1994 Northridge, California, earthquake. Global warming and population growth in arid areas such as the Southwest United States are likely to increase the risk of such hazards.

Research Needs

  • Geographical analysis of cocci incidence in California can be compared to another endemic region to assess different incidence patterns across varied geology, topography, and land use. A predictive model of C. immitis response to climate can be developed through analysis of climate and cocci data.

Other Climate-Related Health Issues

According to the National Agriculture Assessment Group, climate change is expected to bring an increase in pest problems for most locations and most crops studied. If an increase in pesticides is used to counteract the increase in pest problems, the people of California could be more significantly affected than other areas of the country due to the large amount of land in agricultural use in California. A variety of pesticides have been linked directly to human disease and many can harm ecosystems, which could then have indirect (but significant) effects on humans.

As a result of changes in ocean conditions, the distribution and abundance of major fish stocks will probably change substantially. Increased warming of the waters off Los Angeles have resulted in a 50% decline of cold-water, northern fish species (like the greenspotted rockfish), while warm-water southern fish species (like the Garibaldi) have increased by 50%.

To date, 12 California counties have reported the presence of "killer bees" (Africanized Honey Bees, or AHBs). In theory, if climate change leads to wet winters and springs in Southern California, wildflower blooms could alter the distribution of AHBs. Snake bites may follow extreme events such as hurricanes, presumably responding to a change in their habitat caused by changes in rainfall or disturbed nests. Extreme weather events, particularly El Niño-type events, may become more common in California as a result of climate change.

Research Needs

  • Plant pathogens and pests respond to climate; therefore, there is a need to estimate the changing demands for pesticides.

  • Further analyses of the effectiveness of Integrated Pest Management (IPM).

  • Sea surface temperature’s effect on toxic algae and production of fisheries.

  • Ecological studies on hazardous insects and reptiles (e.g., bees and snakes) in response to climate variability.


In California, climate change will contribute to both direct and indirect impacts on human health, as listed above. However, California is uniquely interconnected across many sectors, such as agriculture, fisheries, transportation, recreation, energy, and health. According to the California report of the U.S. National Assessment, "Economy, infrastructure, and natural systems are inextricably linked in California, and a clear understanding of the dynamics of these systems is imperative for the development of informed and systematic response and adaptive strategies." It is therefore essential to further consider integrated assessment modeling of many of the above-listed specific recommendation points. In addition, a general recommendation is to consider the most vulnerable populations for a given risk (and these are discussed in the full report). In many cases, these indirect impacts may be the largest, and yet the most difficult, to study without truly integrated and interdisciplinary research teams.

This roadmap recommends that the following objectives be addressed:

Proposed Research Areas


5.1.1.A Evaluate the effect of heat waves on human health, as well as the current methods and tools for addressing those impacts.
5.1.2.A Assess climate change’s contribution to wildfire risk and the impact of wildfires on human health.
5.1.3.A Study the contributions of extreme climatological events on human health in California, and improve methods for modeling and predicting public health impacts.
5.1.4.A Study the effects of climate change on air quality.
5.1.4.B Study the impacts of climate change-related shifts in air quality on human health.
5.1.5.A Better define the relationships among climate change and vector ecology, and how those relationships affect the transmission of infectious vectorborne diseases.
5.1.5.B Improve monitoring, diagnostic, and evaluation tools.
5.1.5.C Improve data and modeling that addresses infectious vectorborne diseases.
5.1.6.A Evaluate the cause and effect relationships and risks of various climate change-related factors on infectious waterborne diseases.
5.1.6.B Identify high-risk watersheds in California.
5.1.6.C Evaluate and improve tools and methods for addressing infectious waterborne diseases.
5.1.7.A Conduct studies and develop tools to evaluate the potential spread of cocci in California as a result of climate change.
5.1.8.A Evaluate the effect of climate change on pests, pesticides, and their ecological effects.


This roadmap is intended to communicate to an audience that is technically acquainted with the issue. The sections build upon each other to provide a framework and justification for the proposed research and development.

Section 1 states the issue to be addressed. Section 2: Public Interest Vision provides an overview of research needs in this area and how PIER plans to address those needs. Section 3: Background establishes the context of PIER’s climate change work addressing health issues. Section 4: Current Research and Research Needs surveys current projects and identifies specific research needs that are not already being addressed by those projects. Section 5: Goals outlines proposed PIER-EA activities that will meet those needs. Section 6: Leveraging R&D Investments identifies methods and opportunities to help ensure that the investment of research funds will achieve the greatest public benefits. Section 7: Areas Not Addressed by this Roadmap identifies areas related to climate change and health research that the proposed activities do not address. Appendix A: Current Status of Programs offers an overview of work being done to address climate change and health. Appendix B: Health-related Climate Change Publications outlines a broad research base on this topic.

Table of Contents

Executive Summary

Roadmap Organization

1. Issue Statement

2. Public Interest Vision

3. Background

3.1 Future Climate of California

3.2 The PIER Focus

4. Current Research and Research Needs

4.1 Heat Waves

4.1.1 Danger Zones

4.1.2 Heat Index

4.1.3 Urban Heat Islands

4.1.4 Regional Variations

4.1.5 Heat-related Health Outcomes

4.1.6 Vulnerable Populations

4.1.7 Adaptation

4.2 Wildfires

4.2.1 California’s Ecosystems

4.2.2 Conditions Conducive to Fires

4.2.3 Frequency and Intensity of Fires

4.2.4 El Niño-Type Events and Santa Ana Winds

4.2.5 Losses Due to Wildfires

4.2.6 Public Health Impacts

4.2.7 Secondary Events

4.2.8 Regional Variations

4.2.9 Vulnerable Populations

4.2.10 Adaptation

4.3 Extreme Events

4.3.1 Global Warming Impacts

4.3.2 Heavy Precipitation and Flooding

4.3.3 Landslides

4.3.4 Droughts

4.3.5 Sea Level Rise

4.3.6 Post Traumatic Stress Disorder (PTSD)

4.3.7 Vulnerable Populations

4.3.8 Adaptation

4.4 Air Quality

4.4.1 Ozone

4.4.2 Pollen and Allergies

4.4.3 Particulate Matter

4.4.4 Dust

4.4.5 Ozone Depletion and UV Radiation: Potential Link to Climate Change?

4.4.6 Asthma

4.4.7 Co-benefits of Greenhouse Gas Reduction

4.4.8 Vulnerable Populations

4.4.9 Adaptation

4.5 Infectious Vectorborne Diseases

4.5.1 Encephalitis

4.5.2 West Nile Virus

4.5.3 Lyme Disease

4.5.4 Hantavirus Pulmonary Syndrome (HPS)

4.5.5 Plague

4.5.6 Dengue Fever

4.5.7 Malaria

4.6 Infectious Waterborne Diseases

4.6.1 Diarrheal Diseases (cholera)

4.6.2 Fish Poisoning and Harmful Algal Blooms

4.6.3 Vulnerable Populations

4.6.4 Adaptation

4.7 Other Infectious Diseases

4.7.1 Coccidioidomycosis (Valley Fever)

4.7.2 Kawasaki Disease

4.7.3 Vulnerable Populations

4.7.4 Adaptation

4.8 Other Climate-related Health Issues

4.8.1 Agriculture

4.8.2 Pesticides: Increased Exposure with Climate Change?

4.8.3 Marine Fisheries

4.8.4 Killer Bees ( or Africanized Honey Bees, AHBs)

4.8.5 Snake Bites

4.8.6 Vulnerable Populations

4.8.7 Adaptation

5. Goals

5.1 Objectives

6. Leveraging R&D Investments

6.1 Methods of Leveraging

6.2 Opportunities

7. References

Appendix A: Current Status of Programs

Appendix B: Health-Related Climate Change Publications


Table 1. Annual fire outcomes under present and future (double CO2) climate. Effect of population density

Table 2. Association between cocci incidence and selected environmental and climatic variables

Table 3. Proposed research areas


Figure 1. Landslides in California reported from 1998 storms

Figure 2. Potential flooding and landslide areas following the 1997 Baker fire

Figure 3. Comparison of observed and "forecasted" April–June female Cx. tarsalis counts, based on 1973–1990 linear regression with April 1 snow water content in Kern River watershed

Figure 4. Areas of the United States and northern Mexico that are considered endemic for Valley Fever

Figure 5. The seasonal relationship between amount of rainfall and number of cases of cocci in humans in Kern County, California, 1990–1992

Figure 6. Changes in Southern California’s marine ecosystem since the mid-1970s

Figure 7. AHB distribution in 2003

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