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HEAT ISLANDS &
URBAN IMPACTS ON WEATHER AND CLIMATE
Urban Heat Island
Figure 3.30
Urbanization Changes the Environment in 4 Ways:
1. Changes to the radiation balance
2. Changes to the water budget
3. Changes to the circulation patterns
4. Through the addition of heat, water vapor, pollution
The Urban Environment
Figure 3.29
Sacramento, CA
Bright red is about 150F, while blue and green are cool water, veg
Baton Rouge, LA
Salt Lake City
Photograph (left) and thermal image (right) of a dense residential neighbourhood in Tokyo Japan. The skyline of the Shinjuku area of Tokyo is visible in the background. The thermal image was taken in early October during the late afternoon as the urban surface began to cool. The photograph was taken on a different day and is courtesy of M. Roth (National University of Singapore).
Figure 4. Remotely-sensed surface characteristics: (a) tower-mounted thermal image and (b) web-camera image of snow cover from the Montréal urban site (Images provided by O. Bergeron of McGill University and F. Chagnon of Environment Canada); (c) LiDAR extraction of vegetation and derived maximum surface from the urban residential study site (Area=300x300m) in Vancouver (Image provided by N. Goodwin, UBC).
Atlanta’s Urban Heat Island
Increased lightning and rainfall occur downwind of Houston
http://www.gsfc.nasa.gov/gsfc/earth/pictures/20020613urbanrain/Urban%20Heat%20Island.mpg
(animation of rainfall downwind of city)
Greater rainfall shown downwind of Atlanta.
Cities tend to create more rainfall downwind.
http://www.atmosphere.mpg.de/enid/d6276b552c92fc69c88e660a2b435625,0/2__Urban_Climate/-_Air_circulation_3rm.html
Impact on Human healthHeat related illnesses: occur when high ambient temperature overcomes the body’s natural ability to dissipate heat.
1. heat cramps: Heat cramps are strong muscle contractions, usually in the muscles at the back of the calves. Cause: muscular spasms that occur when the body loses too much salt during excessive sweating and not enough salt is taken in.
2. heat exhaustion: Heat exhaustion is characterized by muscle cramps, fatigue, headache, nausea or vomiting, and dizziness or fainting. The skin is often cool and moist, indicating that the body's mechanism for cooling itself (i.e., sweating) is still functioning. The pulse rate is typically fast and weak, and breathing is rapid and shallow.
3. heat syncope (Sudden dizziness, feeling faint and sometimes fainting experienced after exercising in the heat. The skin appears pale and sweaty but is generally moist and cool. The pulse may be weakened, and the heart rate is usually rapid. Body temperature is normal; Causes: by blood pooling in the legs if you have been standing still for a long time in a hot environment. It can also be caused by vigorous physical activity for two or more hours before the fainting happen)
4. Heatstroke: a serious, life-threatening condition characterized by a high body temperature (>103ºF or >39.4ºC); red, hot, and dry skin (no sweating); rapid, strong pulse; throbbing headache; dizziness; nausea; confusion; and unconsciousness.
Symptoms can progress to encephalopathy, liver and kidney failure, coagulopathy, and multiple organ system dysfunction.
Prompt treatment of heat-related illnesses with aggressive fluid replacement and cooling of core body temperature is critical to reducing morbidity and mortality)
Most vulnerable population: children and elderly, and person with chronic medical conditions.
Apparent temperature (AT) or heat index: a measure of body comfort to a combination of air temperature and humidity.
Relative humidity (%)
Temperature (ºC)
Higher humidity, higher apparent temperature.Heat stresses are depend on humidity, wind speed, minimum temperature, radiation load, individual’s ability to perspire, metabolic rate, weight, age, clothing.
Source: Borden and Cutter 2008.
California is Heating Up, Especially in Urban Areas
Los Angeles Civic Center (USC Campus)Average Annual Temperature (1878-2008)
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Year
Deg
rees
F
TEMP
10 Year Avg
Linear (TEMP)
'97'83
'07'31
'59
'44'75
'94
'85
Bill Patzert/JPL Data: NOAA NWS (Los Angeles/Oxnard)
LA's HEATING UP!!
Hot Air = Bad Air
Las Vegas Annual Mean Temperatures, 1940-47,49-2006
y = 0.0583x + 65.025
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Las Vegas Annual Max Temps, 1940-47,49-2006
y = -0.0093x + 80.331
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Las Vegas Annual Minimum Temps, 1940-47.49-2006
y = 0.1258x + 49.721
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Heat Wave Events per Year, 1906-2006
Heat Wave Events Have Increased By More than 3
Frequency of Heat and Cold Days at Civic Center
Frequency of heat and Cold Days at Pierce College
How to combat the UHI?
http://www.harc.edu/Projects/CoolHouston/About/Video
Cool Houston
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.
COOL ROOFS
The aerial photograph at left of Washington, DC, shows the amount of green space and vegetation present in 2002. The photo atright shows how this same area would look in 2025 after a proposed 20-year program to install green roofs on 20% of city buildingsover 10,000 square feet.
Street planters in Portland, OR, are used inhighly developed urban areas to introducegreen space and manage stormwater runoff.
Urban trees intercept rainfall before it hits theground and is converted to stormwater runoff.
A RiverSafe RainBarrel installed at the Jane Holmes nursing residence in Pittsburgh, PA, by the Nine Mile Run RainBarrel Initiative.
For example, researchers atthe University of California at Davis have estimatedthat for every 1,000 deciduous trees in California’sCentral Valley, stormwater runoff is reduced nearly1 million gallons—a value of almost $7,000.4 Clearly,preserving trees reduces polluted stormwater dischargesand the need for engineered controls to replacethose lost functions. When those trees are cut downand their functions are lost, those costs are passed onto municipal governments, which then pass them onto their citizens.
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