Transcript Urban heat island - Cal State LA

California is Heating Up, but It’s
Oh, So Much Worse in the Cities
Steve LaDochy, Professor
Department of Geosciences & Environment, CSULA
Conference on Global Modernities, California State University, Los Angeles, May 4th, 2013
WHAT IS THE URBAN HEAT ISLAND?
Cities tend to be warmer than their rural surroundings, with the peak
of the “island” being located in the Central Business District.
During hot weather, urban temperatures retain heat well into the nighttime.
The Urban Environment
Figure 3.29
Urban materials tend to be less reflective and store
heat to be released at night.
Urban Heat Island-History
The phenomenon was first investigated and described by Luke Howard in the 1810s,
although he was not the one to name the phenomenon.[1] The temperature difference
usually is larger at night than during the day, and is most apparent when winds are
weak. Seasonally, UHI is seen during both summer and winter. The main cause of the
urban heat island is modification of the land surface by urban development which
uses materials which effectively retain heat. Waste heat generated by energy usage is
a secondary contributor.[2] As a population center grows, it tends to expand its area
and increase its average temperature. The less-used term heat island refers to any
area, populated or not, which is consistently hotter than the surrounding area.[3]
California
temperatures have
risen about 2oF
from 1950-2000,
while urban areas
have heated up
much faster.
Urban Heat Island Grows as Cities Grow
HEAT KILLS
• Heat kills by taxing the human body beyond its abilities. In a normal
year, about 175 Americans succumb to the demands of summer heat.
• Among the large continental family of natural hazards, only the cold of
winter -- not lightning, hurricanes, tornadoes, floods, or earthquakes -takes a greater toll.
• In the 40-year period from 1936 through 1975, nearly 20,000 people
were killed in the United States by the effects of heat and solar
radiation. In the disastrous heat wave of 1980, more than 1,250 people
died.
HEAT KILLS
• Heat kills by taxing the human body beyond its abilities. In a normal year,
about 175 Americans succumb to the demands of summer heat.
• In the 40-year period from 1936 through 1975, nearly 20,000 people were
killed in the United States by the effects of heat and solar radiation. In the
disastrous heat wave of 1980, more than 1,250 people died.
2003 KILLER HEAT WAVES CROSSES EUROPE
2003 Heat Wave: between twenty to thirty-five thousand people -- the
majority dying in the hottest period during the first two weeks in August.
The worst hit was France which lost more than 14,000 of it mostly elderly
population in the unrelenting heat recorded as high as 104 degrees temperatures that didn't cool down even at night. The event marks the
2003 European heat wave as the hottest summer in the northern
hemisphere.
About 15,000 deaths were related to the 2003 heat wave mostly in French cities where
elderly were not prepared for 100+ temperatures.
The Great Russian Heat Wave of 2010 is one of the most intense,
widespread, and long-lasting heat waves in world history. Only the
European heat wave of 2003, which killed 35,000 - 50,000 people, and the
incredible North American heat wave of July 1936, which set all-time
extreme highest temperature records in fifteen U.S. states, can compare. All
of these heat waves were caused by a highly unusual kink in the jet stream
that remained locked in place for over a month. The jet stream is an upperlevel river of air, between the altitudes of about 30,000 - 40,000 feet
(10,000 - 12,000 meters).
St. Louis Frequency of Warm, Humid Air Masses
St. Louis experienced an average of three annual
three-day-or-longer runs of dangerously hot air masses
in the 1940s. That number has more than doubled,
to an average of seven such heat waves today.
Chicago & St. Louis Air Mass Frequency Trends:
Cold Weather Type- Dry Polar (DP)
Chicago: 7.3 less DP days today than in the 1940’s
St. Louis: 3.7 less DP days today than in the 1040’s
Source: Heat in the Heartland, UCS
Source: Heat in the Heartland, UCS
New Orleans, LA. electrical load can increase steadily once temperatures
begin to exceed about 68–77°F (20–25°C). Other areas of the country
show similar demand curves as temperatures rise. (EPA)
New York City Energy Consumption rises with temperatures.
“Right now, we average about 14 days each summer above 90 degrees [in New York]. In a couple decades,
we could be experiencing 30 days or more” .
“So we have two forces—urban heat islands and global warming—that are reinforcing each other and are
going to create hot, hot conditions for more than half the world’s population,” Gaffin explains. “How do we
make cities more habitable in the future?”
Phoenix’ Urban Heat Island
Summer nights are warming even faster in Phoenix, Arizona.
Heat Waves in Southern California:
Are They Becoming More Frequent
and Longer Lasting?
Arbi Tamrazian, UC Berkeley , Steve LaDochy,
California State University, Los Angeles,
Josh Willis and William C. Patzert, JPL
Acclimatization to Heat Waves in Rome
Mitigation: Trees and vegetation
Mitigation: Cool Roofs
COOL ROOFS
Potential net energy savings from changing roof
reflectivity. Savings are measured in dollars. Note that
the net savings are the savings of cooling energy use
less the penalties of heating energy use.
Mitigation: Green Roofs
For example, researchers at
the University of California at Davis have estimated
that for every 1,000 deciduous trees in California’s
Central Valley, stormwater runoff is reduced nearly
1 million gallons—a value of almost $7,000.4 Clearly,
preserving trees reduces polluted stormwater discharges
and the need for engineered controls to replace
those lost functions. When those trees are cut down
and their functions are lost, those costs are passed on
to municipal governments, which then pass them on
to their citizens.
Mitigation: Cool Pavements
MITIGATION STRATEGIES
GREEN (ECO)CITIES
Ecocity (sustainable city): an ecologically healthy city. It is to
enhance the health and quality of life of their inhabitants and
maintain the ecosystems on which they depend. It minimizes
the input of energy, water and food and its wastes, output of
heat, air pollution, and water pollution.
http://www.harc.edu/Projects/CoolHouston/About/Video
Cool Houston
Increased lightning and rainfall occur downwind of Houston
Cities tend to create more rainfall downwind.
http://www.gsfc.nasa.gov/gsfc/earth/pictures/20020613urbanrain/Urban%20Heat%2
0Island.mpg
(animation of rainfall downwind of city)
Greater rainfall shown downwind of Atlanta.
http://www.atmosphere.mpg.de/enid/d6276b
552c92fc69c88e660a2b435625,0/2__Urban_Cl
imate/-_Air_circulation_3rm.html
The aerial photograph at left of Washington, DC, shows the amount of
green space and vegetation present in 2002. The photo at
right shows how this same area would look in 2025 after a proposed 20year program to install green roofs on 20% of city buildings
over 10,000 square feet.
Street planters in Portland, OR, are used in
highly developed urban areas to introduce
green space and manage stormwater runoff.
Questions?