A healthy urban forest in San Diego can conserve energy - A proposal

by Holly Duncan


    This letter was presented on October 10, 2001 at the San Diego City Council Rules Committee, chaired by Mayor Dick Murphy. It was referred to the City Manager for review and recommendations.

ne purpose of today's Rules Committee meeting is to further address California's “Energy Crisis” and look for local solutions that will aid in achieving one of Mayor Dick Murphy's stated goals, Goal #9: “Pursue energy independence.”

    Today I propose to this committee that planting large, broad-canopied trees in the city's rights-of-way would be one of the most cost-effective activities the city could undertake to advance the mayor's goal.

    Our grandparents, lacking the modern day creature comforts of central heating and air conditioning, used trees to modify and regulate the climates of their homes; and with far less environmental damage than today's modern conveniences (Weather-Wise Gardening; Ortho Books; 1974,1978; pg.3).

    As USDA researchers state in their brochure “Save Dollars With Shade”:

    “Imagine a solution to our energy crisis as simple a planting a tree. We've all grown up with trees, climbed in them, and possibly even planted a few. But how many of us know that they significantly contribute to cooling our homes, businesses and communities?”

    Incontrovertible, scientific studies prove that trees in communities do this. Here's how:

  • Shading, which reduces the amount of radiant energy absorbed and stored by built surfaces.
  • Evapotranspiration, which converts liquid water in leaves to vapor, thereby cooling the air.
  • Reducing the velocity of wind, which slows the infiltration of outside air into inside spaces.

    Trees planted in large quantities in a carefully planned and scientific manner in cities are the most cost-effective tool a city can employ to mitigate what scientists refer to as the Urban Heat Island (UHI) phenomenon. Scientists studying this phenomenon believe that billions of dollars are spent each year just to compensate for the increased heat of an Urban Heat Island. We shall see why.

Urban heat islands


    As many residents can tell you, cities can be very hot places during the summer. The air in a city can be 6-8 degrees F hotter than the surrounding countryside. Scientists call these cities “Urban Heat Islands.” Their causes are:NT>

  • Fewer trees, shrubs and other plants to shade streets and buildings, intercept solar radiation, and cool the air by “evapotranspiration”
  • Buildings and pavement made of dark materials absorb the sun's rays instead of reflecting them away, causing the temperature of the surfaces and the air around them to rise.

    Scientists have been tracking the warming of cities for decades. It is estimated that half the US population lives in heat islands and, as the chart below shows, San Diego is fast becoming a serious one. We are heating up at the same rate as Los Angeles.

    Urban heat islands cause:

  • Increased discomfort.Increased summertime temperatures cause increased discomfort. This discomfort often is expressed in increased medical events as a result of:
  • Increased Smog.Smog formation is highly sensitive to temperature; the higher the temperature, the higher formation and concentration of smog. It's the “Bunsen burner” effect. In Los Angeles, one of the research pilot projects show that, at temperatures below 70 degrees, smog is below national (health protective) standards. The scientists estimate that for every one degree increase in temperature, smog risks increase 3%. Since good doctors tell their patients (sensitive groups) to stay indoors and run the air conditioner on “bad air” days, this is an additional contributor to:
  • Increased Demand for Cooling.Using the same Los Angeles example, scientists estimate that every 1 (one) degree above 70 F results in a 2% increase in the demand for cooling power. The scientists estimated that about 1 to 1.5 gigawatts of power are used to compensate the impact of the Los Angeles heat island. At 1996 or earlier rates, this was estimated to cost Southern California Edison's customers about $100,000 per hour, about $100 million per year. In today's deregulated market, these figures would most likely increase.

Fiscal impacts of urban heat islands


    In the Los Angeles research pilot project, scientists assigned a dollar value to these impacts. The Los Angeles Urban Heat Island impacts were projected to be:

  • Extra direct costs for cooling = $100M/year calculated at $0.10/kwh for peak electricity cost
  • Extra indirect costs for cooling = $70 M/year
  • Smog costs (health costs) = $360M/year
  • Total Costs = $530M/year

QUESTION: What are the fiscal impacts of San Diego's urban heat island?

ANSWER: The exact figure is unknown, but you can assume mega-bucks.

    While we have documented the costs of L.A.'s UHI, other pilot cities studied showed similar results. It is safe to assume that San Diego's UHI is generating significant fiscal impacts to your constituents; easily in the many millions of dollars.

Mitigation of urban heat islands = “cool communities”


    Measures to “cool” Urban Heat Islands are simple and have been known to human beings for ages: reflective surfaces and trees. The scientists recommend:

  • Lighten Up.Reflective, light colored roofs and pavement reflect solar radiation. Dark surfaces act as “heat sinks” by absorbing the radiation and holding the heat in a city. Light colored surfaces reflect the heat away from the city. So the key is to Lighten Up those surfaces.
  • VegetationLarge trees that shade streets and structures result in reduced neighborhood ambient temperatures. Scientists know, when abundant foliage shades any of these “heat sinks”, their temperatures plummet. This is true even for light-colored surfaces. For cooling, you just can't beat nature's “air conditioners”: trees.

    Incontrovertible, scientific evidence exists to document that use of these two simple measures will:

  • Reduce cooling energy use
  • Reduce emissions (greenhouse gases)
  • Reduce smog

    As we have seen from the Los Angeles research pilot project, lightening up and reforesting can produce Big Bucks Savings for cities.

    In 1997, heat island scientists stated that Americans are “paying dearly” for this extra heat. “One sixth of the electricity consumed in the United States goes to cool buildings at an annual power cost of $40 billion” (“Painting the town white and green,” MIT's Technology Review, Feb.-March 1997, pg 3). On page 5 of the same article they continue: “...implementing these cool community measures [in Los Angeles] would lower the need for peak electrical generating capacity by about 1,500 megawatts - equivalent to two to three large power plants.” [emphasis added]

    A 1998 Newsweek article quoted Dr. Hashem Akbari, principal investigator of the heat islands project at DOE's Lawrence Berkeley Laboratory thusly: “...a 4-degree temperature drop in summer temperatures could be achieved in L.A. by planting trees over 5 percent of the city's area - about 10 million trees - and replacing dark roofs and blacktop with lighter-colored materials.... A more aggressive program could have an even greater impact. 'Cooling LA by 4 degrees,' says Akbari, 'would have the same magnitude effect [on smog] as turning all of the on-road vehicles into electric cars. This is so huge, nothing else compares.'” [emphasis added]

    In another publication, Dr. Akbari indicated that in mild climate areas, such as San Diego, it is possible that all air conditioning requirements could be obviated through UHI mitigation.

    If the “cheapest and cleanest” energy is the energy we don't use, then clearly the “Cool Communities” mitigation program is a winner!

    Thus far, we have concentrated on Los Angeles. For comparison, let's look at the results of another project city: Chicago. It is believed that Chicago's UHI played a role in the many deaths in that city during a heat wave in the early 90s. Their mitigation, primarily focused on tree planting, revealed these interesting results:

  • Air Quality benefits in 1991 worth $9.2 million.
  • Carbon sequestration = 155,000 tons/year, helping to reduce the greenhouse effect and global warming. They also reduce building energy use for heating and cooling, which in turn reduces carbon emissions from power plants by about 12,600 tons/year.
  • Large trees remove 60 to 70 times more pollution and store up to 1000 times more carbon than small trees.
  • Although street trees account for only 10% of the city's trees, they make up 24% of total leaf surface area because they are older and larger than off-street trees.
  • Trees provide net benefits worth 2 to 3 times the cost of planting and caring for them over a 30-year period.
  • Greatest savings for energy, air quality and water were derived from residential tree plantings, closely followed by street tree plantings.

    In addition to the demonstrated energy/air quality/water benefits provided by a thriving urban forest, there are ancillary benefits as well, which include:

  • Noise reduction
  • Wildlife habitat
  • Reduce surface runoff and protect urban water
  • Enhance the aesthetic quality of life in the city; create feelings of relaxation and well-being; provide privacy and a sense of solitude and security.
  • Increase property values.
  • Increase economic stability by attracting business and tourists.
  • Reduce glare (indirect health benefits: cataracts and skin cancer)

    These benefits appear to directly or indirectly address additional goals of Mayor Murphy:

  • #3: Create neighborhoods we can be proud of (direct).
  • #4: Clean up our beaches and bays (direct).
  • #2: Reduce traffic congestion (indirect, by making communities more pedestrian-friendly).
  • #8: Make San Diego America's safest city (trees' calming effect: the City of Irvine claims it is the safest city and they have lots and lots of trees - your call on direct/indirect).
  • #10: Complete MSCP open space acquisitions (indirect, habitat: large trees provide nesting spaces; small trees roosting spaces.).

    Planting trees to conserve energy is not new knowledge. As already stated, our grandparents had this knowledge. In recent decades, however, this subject has been the focus of intense scientific study by the US Department of Energy, the USDA Forest Service, the Lawrence Berkeley National Laboratory, and the US EPA.

    It is interesting that, during the OPEC energy crisis of the 1970s, the California legislature passed a bill titled: “The Urban Forestry Act of 1978” (Ca. Public Resources Code Sect. 4799.o6 - 4799.12) which declared city trees to be energy conserving “valuable economic assets” to cities. More recently, in 1993, based upon more research, the California legislature passed Government Code 53067, which states: “As canopy cover increases the public benefits increase.”

    How sad that the City of San Diego appears to have not heard these important messages.

San Diego's urban forest


    Like all major metropolitan cities in the United States, San Diego has been losing its urban forest at alarming rates over the past 25 years. But unlike other major urban areas in California that appear to have understood the message of the importance of tree stewardship contained in the Urban Forestry Act of 1978 (as evidenced by their membership as “Tree Cities” with the National Arbor Day Foundation; in many cases for almost 20 years), San Diego appears to have missed the boat. San Diego is anything but a “Tree City.”

    In 1993, People For Trees, with assistance from SANDAG, prepared a State of the Urban Forest report for the San Diego Region. In this report one learns:

    “The City of San Diego has the largest tree care budget, but no planting budget...1968 was the last year money was budgeted for new street tree plantings and 1974 was the last year any funds were budgeted for replacement street trees.” [emphasis added].

    Also reported, as of 1993:

    “...An additional 934,000 street trees would need to be planted to meet the national standard [US Park and Recreation] of 200 street trees per mile for our 7,024 miles of streets.”

    Sadly, we learn that San Diego's canopy cover in 1993 was, at best, only 19% of this standard, while a minimum of 40% overall is the recommended percentage. Further:

    “Tree removals continue and have recently ranged from 300 to 500 annually.”

    That was in October 1993. Monthly tree removal lists from the City's Street Division for District Six for the recent several years reveal that District Six is losing anywhere from 200 to 300 trees annually, all by itself! This raises the following questions:

  • What is the current annual tree loss citywide?
  • What is San Diego's current fraction of the national standard for street trees?
  • What part of that number are mature, large, broad-canopied trees that provide the public the greatest benefit?
  • What is the reason for the apparent intensification of removal without a concomitant replacement program?
  • Why aren't street trees under Park and Recreation jurisdiction?
  • Is San Diego's tree policy/program California Environmental Quality Act compliant?

    If the current budget is anything like 1993's with regard to trees, then it is possible that the only tree-planting (UHI mitigation; CEQA mitigation) occurring in the City of San Diego is that done by citizen volunteers working with the nonprofit People For Trees, funded only by grants and donations. It is disingenuous to say that this approach to “stewardship” of San Diego's Urban Forest (defined by statute as “valuable economic assets”) on the part of California's second largest city is an appropriate and serious effort. Further, it is doubtful that such a tree-planting program will be a resounding success. The 1994 Clairemont planting is a failure. As a taxpayer, ratepayer and mother of an asthmatic, I assert that the City of San Diego's current tree policy inflicts a grave disservice on your constituents.

    The current situation, whether as a result of either ignorance or bad policy, borders on the criminal. Flushing many millions of dollars of your constituents' hard-earned money down the toilet for expensive “fixes” to problems known to be caused by clear-cutting urban forests qualifies to be classified as (in the now-famous words of a former San Diego council member) “felony stupid.” Therefore, the city's current approach to tree stewardship is unquestionably unacceptable and is long overdue a remedy.

    If we can agree that a city's urban forest can be a source of tremendous civic pride on the part of a community, as it was when nearly the entire city turned out to plant trees in Balboa Park before the opening of the 1915 Panama California Exposition, then the profound loss of that same urban forest, as is being witnessed in San Diego, can only be described as an indicator of a form of civic disease. As with all diseases, the cause of this disease must be discovered, and a cure immediately secured. To that end, I have attached a list of specific proposals [see page 6] to: (1) Halt the decline of San Diego's Urban Forest, and (2) Mitigate San Diego's Urban Heat Island. I request this committee embrace these proposals TODAY! BEGIN THE REMEDY NOW!



    As I have attempted to demonstrate, Urban Heat Islands endanger the public, both physically and fiscally. Implementation of the “Cool Communities” mitigation measures recommended by the experts and presented here today would set the City of San Diego on an appropriate course of action for providing healthy ecosystems and communities, “creating neighborhoods we can be proud of,” moving constituents toward “energy independence,” thereby enhancing the quality of life for both residents of and visitors to San Diego. It would, indeed, present the possibility that by the year 2020 we might all agree we are living in a city “Worthy of Our Affection.”

    Should the City of San Diego decide not to implement the “Cool Communities” programs outlined today, deciding on the basis of the usual “sunny town” mentality that none of this applies to San Diego, preferring instead to continue on its current path of default tree stewardship, thereby subjecting constituents to higher electricity bills and increasingly degraded air quality (soon rivaling that of Los Angeles or Houston; this can be readily documented by the San Diego County Air Pollution Control District), I suggest they owe their constituents a detailed explanation as to precisely why more than one million residents of the City of San Diego should be required to forego the scientifically documented, irrefutable benefits of living in “Cool Communities.”

    You might also wish to explain your plan for ensuring that, by the year 2020, San Diego will be a city “Worthy of Our Affection.”

    Respectfully submitted,

    Holly Duncan

    3838 Mt. Blackburn Avenue

    San Diego, Ca. 92111

“They took all the trees
nd put them in a tree museum...
nd they charged all the people
dollar and a half just to see 'em...
on't it always seem to go
hat you don't know what you've got...
ill its gone
hey've paved paradise
nd put up a parking lot.”

    -- Joni Mitchell


Humankind Has Not
oven the Web of Life
e Are But One
hread Within It.
hatever We Do To the Web
e Do To Ourselves.
ll Things Are Bound Together.
ll Things Connect.

   -- Chief Seattle


To Learn More about Urban Heat Islands and Urban Forestry


State of California Urban & Community Forestry Coordinator: Eric A. Oldar

The Resources Agency
epartment of Forestry & Fire Protection
ierra South Region Office, Riverside
424 Mulberry Street
iverside, CA. 92501
909) 782-4140 Ext. 6125

Lawrence Berkeley National Laboratory - Urban Heat Island Group

Building 90, Room 200
erkeley Lab
erkeley, CA. 94720
510) 486-7437

Center for Urban Forest Research - Pacific Southwest Research Station

USDA Forest Service
Shield Avenue, Su. 1103
avis, CA. 95616-8587
530) 752-6834

American Forests - www.americanforests.org

PO Box 2000
ashington, D.C. 20013
202) 955-4500

National Arbor Day Foundation - www.arborday.org

100 Arbor Avenue
ebraska City, NE. 68410
402) 474-5655

Landscaping For Energy Conservation [Residential]:

1) U.S. Department of Energy - Energy Efficiency and Renewable Energy Clearinghouse

(800) 363-3732
P.O. Box 3048
Merrifield, VA. 22116

Brochure #FS220, April 1995 “Landscaping for Energy Efficiency”

2) California Energy Commission - www.energy.ca.gov

Visit the: “Consumer Energy Center”; good ideas at: “Choices at Home & Work"


    California Public Resources Code Sect. 4799.06 - 4799.12.; California Urban Forestry Act of 1978 [Passed by the State Legislature during the 1970s Energy Crisis.]

    California Government Code 53067 (Tree Pruning Standards); passed 1993.

    California Environmental Quality Act (CEQA), commencing with Sect. 21000 of the Public Resources Code.; 1970.

    You can contact Holly Duncan via email to: hollydznet.com



  • Embrace and Implement the “Cool Communities” strategies developed by the US Dept. of Energy & USEPA to mitigate Urban Heat Islands as outlined here today.
  • Make it a city council priority to immediately develop and adopt an Urban Heat Island Mitigation Program that has the two goals:
    • Lightening the color of surfaces
    • Massive reforestation of the city to shade streets and structures based on the sciences of UHI abatement and urban forestry practices, assigning the trees' needs, and the vital role they play in the mitigation process, top priority.
  • Establish standards of achievement and mandate achievement no later than the year 2020. Set milestones and strive to achieve them early.
  • Declare a citywide moratorium on any further mature tree removals; authorize removal of only dead or hazardous trees, and clearly define the term hazardous.
  • Give responsibility for planting and maintenance of the city's street trees back to the tree experts - the Department of Park & Recreation - and fund their requirements.
  • Immediately commit to the National Arbor Day Foundation's “Tree City Standards” and make application for San Diego to become a “Tree City.”
  • Send at least one delegate to the December 2001 Multi-Disciplinary Conference of Cal/EPA in Sacramento, “Planting Low-Emitting Urban Forests from California's Changing Landscape: Research, Application, and Funding,” to learn more about the connections of UHIs, global warming, tree planting and air quality concerns.
  • Review city policy with regard to Urban Forestry in San Diego. Discover what San Diego did when it still had an Urban Forest, and replicate it.
  • Set a goal of achieving a minimum of 40% canopy cover overall for the City of San Diego by the year 2020; put a plan in place to accomplish this and make it happen!
  • Incorporate “Cool Communities” surface lightening strategies into the City of San Diego Building Codes.
    • Participate in the “Cool Roofs” program of the S.D.R.E.O. Install as many “Cool Roofs” on city-owned buildings as possible, qualifying for the rebate. Bring our hard-earned taxpayer dollars back to San Diego!