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 4 th , 2013. WHAT IS THE URBAN HEAT ISLAND?.
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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.
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. 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. 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.
California temperatures have risen about 2oF from 1950-2000, while urban areas have heated up much faster.
Urban Heat Island Grows as Cities Grow
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 upper-level 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
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
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.
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 20-year 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.