Climate and the Natural Environment




  • The annual number of days with “Good” air quality has increased since 2009 to a high of 310 in 2016; however, there is no clear indication that the trend toward improvement is permanent and more frequent wild fires may jeopardize progress.
  • The South of Market neighborhood is the most impacted by air pollution exposure.
  • San Francisco lags behind peer cities in tree canopy coverage – some neighborhoods have less than 5% coverage.
  • San Francisco has made significant progress towards greenhouse gas reduction goal, largely due to reducing residential and landfill organics emissions.
  • Thee neighborhoods with the greatest extreme heat vulnerability include Chinatown, Tenderloin, South of Market, Japantown, and Mission.
  • The neighborhoods that are most vulnerable to the negative health effects associated with flooding include South of Market, Bayview, Tenderloin, and North Beach.

What is it?

Climate and Natural Environment refers to both 1) the preservation and protection of San Francisco’s natural features such as land, water, air, and atmosphere, and; 2) the impact of extreme weather events on human health and well-being.


Why is it important for health?

Human health is affected by the natural environment. Burning fossil fuels—coal, oil, gas—releases greenhouse gases (GHGs) into the atmosphere, which traps heat and causes temperatures to increase. This causes more variable weather: heat waves, extreme storms and sea level rise, droughts, air pollution, and wildfires. These weather events have significant and cascading impacts on public health.

Air Quality: Air quality impacts public health. [1] These health impacts are largely influenced by proximity to high-traffic corridors and industrial areas. Density influences air quality. Large buildings block wind and prevent the dissipation of pollution. Urban heat islands can accelerate the creation of ground-level ozone. Ground-level ozone increases rates of asthma attacks, shortness of breath, coughing, chest-tightness, irritated mucus membranes, pulmonary inflammation, and respiratory illnesses and diseases. PM2.5 concentration exacerbates asthma, bronchitis, and acute and chronic respiratory disease. These ailments will especially affect children because their lungs are still developing, and because their faster breathing rates increase their exposure to pollutants. In adults, worsened air quality from ground-level ozone or other pollutants could increase rates of chronic lung disease such as emphysema and premature death.

Climate change is anticipated to impact local air quality. Drought can impact air quality as wildfires in adjacent counties can increase concentrations of ozone and particulate matter in San Francisco. Heat influences the creation of ground level ozone and the City should expect a small increase in these ozone levels. Communities that are currently most exposed will suffer the worst of the changes. Groups that are less physically capable of dealing with the health impacts, like children and older adults, as well as those who have little protection from outdoor air, like the homeless, are most vulnerable to changes in air quality.

Tree Canopy: Tree Canopy (UTC) is defined as the layer of leaves, branches and stems of trees that cover the ground when viewed from above. Trees provide a wealth of benefits: they create natural cooling by shading streets and buildings, which lowers the risk of skin cancer by reducing exposure to ultra-violet (UV) radiation; they reduce energy demand and consumption; they capture air pollutants; they reduce atmospheric carbon dioxide; they produce oxygen; they help capture storm-water runoff, and filter the water, lowering the amount of mercury, oil, and lead flowing into the Bay. [2] Trees can also serve as buffers between pedestrians and auto traffic, potentially reducing pedestrian injuries. Several studies indicate that forests, trees and other vegetation provide psychological benefits as well: for adults they can improve recovery from mental fatigue. [3], [4] This in turn can reduce socially unacceptable behaviors and crime, which can help reduce behavior problems among children.

​Greenhouse gas emissions: Greenhouse gases (GHGs) capture heat from the sun in the earth’s atmosphere, warming the earth’s land surface and bodies of water. GHGs present in the atmosphere include carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6). Anthropogenic (human generated) emissions of these gases has increased their prevalence in the atmosphere since the start of the industrial revolution. GHGs contribute to climate change—which directly and indirectly impacts public health. [5] Many strategies that can reduce GHG emissions also serve to promote good health. Substituting active transportation—walking, bicycling, using mass transit—for driving cars would have a major impact on GHG emissions, since the transportation sector overall contributes the second-largest share of greenhouse gas emissions. Vegetable-based diets that limit meat, dairy, and poultry, and rely more on fresh rather than processed foods result in better health outcomes, including lower rates of cardiovascular disease, type II diabetes, and some cancers. The Food and Agriculture Organization of the United Nations estimates that livestock production alone may account for 18 percent of global greenhouse gas emissions. Due to the resource intensiveness of processing food and producing meat, a largely plant-based diet is also better for the environment.

Extreme Heat: An extreme heat event is defined as a day where temperatures reach the 98th percentile of temperatures of all days for that specific location. In San Francisco, of all days between 1961 and 1990, the 98th percentile of temperatures equals about 85 degree Fahrenheit. Currently, San Francisco averages about 5-6 extreme heat days per year. This number is expected to reach 17 by the end of the century and is prone to year-to-year fluctuations. [5] Direct impacts of extreme heat includes increases in heat-re­lated illnesses such as heat-stroke, dehydration, and heat-related mortality such as heart disease. High temperatures can also exacerbate the impact of pre-existing conditions such as diabetes, renal disease, and many mental health conditions. An analysis of the 2006 California heat wave found significant increases in a wide range of morbidities statewide, with the highest increase in rates of emergency room visits for heat-related illness in cooler climates like San Francisco. San Francisco is a temperate city with housing and infrastructure built for a coastal climate. As San Francisco has not historically experienced extreme heat events or heat waves, San Franciscans have a more difficult time thermo-regulating. As a result, San Franciscans are also at higher risk for largely preventable heat-related illnesses. While everyone is vulnerable to heat-related illness, certain populations are more at risk, including the elderly, low-income, and those with chronic mental health disorders and pre-existing medical conditions.

Flooding and Extreme Storms: As the atmosphere warms, both the melting of the polar ice caps and the thermal expansion of the oceans will cause sea levels to rise. Additionally, climate models predict storms to become more frequent and extreme. These extreme storms are associated with high storm surge and heavy precipitation and will cause flooding along San Francisco’s coast and in the City’s interior. Extreme storms, sea level rise, and flood inundation are associated with many direct health outcomes including respiratory illnesses from in-home dampness and mold, waterborne illness from direct contact with floodwaters, and physical injuries. [6] However, extreme storms may have a greater impact indirectly as power outages associated with extreme storms negatively impact a broad range of health, household, and economic needs.


What is the status in San Francisco?

Air Quality: Between 2000 and 2007, the number of “Good” air quality days remained relatively steady, between 244 and 291, and then fell to a low of 197 in 2009. The annual number of days with “Good” air quality has increased since then to a high of 310 in 2016; however, there is no clear indication that the trend toward improvement is permanent. The number of days with “Good” air quality was 276 in 2017 (Figure 1). During the 2017 fires in Napa and Sonoma counties, San Francisco’s AQI reached 127 and 136, which are “unhealthy for sensitive groups” – this demonstrates that as wildfires in surrounding areas become more frequent because of climate change, air quality may decline even as we reduce local emissions. More information how San Francisco’s air quality compares to peer cities can be found on the Controller’s Office Benchmarking Website.

Air pollution exposure is not evenly distributed across San Francisco. Neighborhoods with heavily trafficked roads are more impacted. An air pollution exposure zone (APEZ) map was developed to show areas within the City with elevated air pollution levels. In 2008, San Francisco Health Code Article 38 was adopted to require new residential construction projects located in the APEZ to install enhanced ventilation to protect residents from the respiratory, heart, and other health effects of living in a poor air quality area. The APEZ is based on modeled concentrations of fine particulate matter (PM2.5), and excess cancer risk from toxic air contaminants (TACs), and a health vulnerability layer. The model includes mobile sources (cars, trucks, rail emissions, and marine sources) as well as stationary source emission from permitted sources (such as gas station, autobody shops, and diesel generators). Figure 2 shows the proportion of residents estimated to be currently living in the APEZ. South of Market has by far the highest level of exposure, with 94% of residents living in the APEZ. Other neighborhoods with high exposure include Financial District/South Beach (76%), Tenderloin (48%), and Mission Bay (40%). When comparing air pollution exposure by Areas of Vulnerability (AOV), about 21% of residents living in areas designated as an AOV are in the APEZ, compared to 7% of residents in the rest of the city (Figure 3).

Tree Canopy: Approximately 13.7% of the surface area in San Francisco is covered by trees. This compares to 21% in Los Angeles, 24% in New York City, 17% in Chicago and 23% in Seattle. [2] In San Francisco, The neighborhoods on the eastern side of the city have the lowest tree canopy coverage (Figure 4). Mission Bay, South of Market, and Tenderloin all have less than 5% canopy coverage. Parts of the city that are designated as Areas of Vulnerability (AOV) have only about 11% tree canopy, compared to 16% in the rest of the city (Figure 5).

Greenhouse Gas Emissions: Compared to the nine Bay Area counties, San Francisco has the lowest per capita greenhouse gas emissions. [7] The low per capita GHG emission rate is largely a result of lower surface transportation emissions and non-residential natural gas consumption. San Francisco has an ambitious goal to achieve zero greenhouse gas emissions by 2050. Figure 6 demonstrates that since 2000 there has been a steady decrease in emissions and the city is on its way towards meeting that goal. The biggest emissions reductions have come through reducing emissions generated by buildings and landfill organics.

Heat Vulnerability: The Heat Vulnerability Index uses socioeconomic and demographic, exposure, health, and infrastructure indicators to identify communities most likely to be affected by the health impacts of extreme heat. In 2013, the neighborhoods that had the greatest extreme heat vulnerability included Chinatown, Tenderloin, South of Market, Japantown, and Mission (Figure 7). For more information, visit the San Francisco Climate and Health Program (

Flood Vulnerability: The Flood Health Vulnerability Index uses socioeconomic and demographic, exposure, health, and housing indicators to identify communities most likely to be affected by the health impacts of flooding, sea level rise, and extreme storms. In 2016, The neighborhoods that were most vulnerable to the negative health effects associated with flooding included South of Market, Bayview, Tenderloin, and North Beach (Figure 8). For more information, visit the San Francisco Climate and Health Program (


What is currently being done in San Francisco to improve health?


Data Sources

USEPA United States Environmental Protection Agency. “Air Quality Index Report.”
SFDPH San Francisco Department of Public Health, Air Quality Enforcement Program.
SFDOE San Francisco Department of Environment.
SFP San Francisco Planning Department, via DataSF.
SFDPH San Francisco Department of Public Health, Climate and Health Program.


Methods and Limitations

Areas of Vulnerability: Areas of Vulnerability (AOV) were created as a way to examine geographic data in relation to populations of concentrated socioeconomic disadvantage. The criteria to be designated as an AOV were:

  1. Top 1/3rd of tracts for < 200% poverty or < 400% poverty & top 1/3rd for persons of color OR
  2. Top 1/3rd of tracts for < 200% poverty or < 400% poverty & top 1/3rd for youth or seniors (65+) OR
  3. Top 1/3rd of tracts for < 200% poverty or < 400% poverty & top 1/3rd for 2 other categories (unemployment, completing high school or less, limited English proficiency persons, linguistically isolated households, or disability)

Tracts that had unstable data for an indicator were automatically given zero credit for that indicator.

Air Quality Index: The air quality index (AQI) is based on the relative levels of and federal standards for each of the six major air pollutants: ozone, particulate matter 2.5, sulfur dioxide, nitrogen dioxide, particulate matter 10, and carbon monoxide. AQI ratings below 100 (ratings of “good” and “moderate”) should not affect the health of the general public, although a “moderate” rating (50-100 AQI) may affect unusually sensitive people.

Heat and Flood Vulnerability: Information on how the heat and flood vulnerability indexes were generated can be found at http://sfclimatehealth.or

Hospitalizations and Emergency Room Visits:
Hospitalization and ER rates measure the number of admissions or visits, not the number of residents who are hospitalized. Admissions records may include multiple admissions by the same person.

​In October 2015, the diagnosis coding standard for Hospitalizations and Emergency Room visits was changed from ICD-9 to ICD-10. Caution should be used in comparing data using the two different standards.

The following ICD-9 and ICD-10 codes were used to identify visits due to heat:
ICD-9: 9920, 9921, 9922, 9923, 9924, 9925, 9926, 9927, 9928, 9929, E9000, E9009
ICD-10: T670, T671, T672, T673, T674, T675, T676, T677, T678, T679, X30X
Estimates for heat as the primary cause were obtained by searching the primary diagnosis field only while estimate for heat as the primary, co-morbid, or coexisting cause was obtained by searching all available diagnosis fields.

Population estimates for rates:

  • State of California, Department of Finance, Race/Hispanics Population with Age and Gender Detail, 2000–2010. Sacramento, California, September 2012.
  • California Department of Finance. Demographic Research Unit. 2018. State and county population projections 2010-2060 [computer file]. Sacramento: California Department of Finance. February 2017.

Standard Population for age adjustment:

  • Population Projections of the United States by Age, Sex, Race, and Hispanic Origin: 1995 to 2050. U.S. Department of Commerce, Economics and Statistics Administration, BUREAU OF THE CENSUS



[1] San Francisco Planning Department, “Air Quality Community Risk Reduction Plan.” [Online]. Available: [Accessed: 07-Sep-2018].
[2] San Francisco Planning Department, “San Francisco Urban Forest Plan,” San Francisco Planning Department, San Francisco, CA, Fall 2014.
[3] F. E. Kuo and W. C. Sullivan, “Environment and Crime in the Inner City: Does Vegetation Reduce Crime?,” Environment and Behavior, vol. 33, no. 3, pp. 343–367, 2001.
[4] A. F. Taylor, F. E. Kuo, and W. C. Sullivan, “Coping with ADD: The Surprising Connection to Green Play Settings,” Environment and Behavior, vol. 33, no. 1, pp. 54–77, 2001.
[5] Cal-Adapt, “Exploring California’s Climate Change Research.” [Online]. Available: [Accessed: 09-Oct-2018].
[6] San Francisco Department of Public Health-Program on Health, “Understanding the Risk: An Assessment of San Francisco’s Vulnerability to Flooding and Extreme Storms,” San Francisco, CA, 2016.
[7] Metropolitan Transportation Commission, “Greenhouse Gas Emissions,” Vital Signs. [Online]. Available: [Accessed: 07-Sep-2018].