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

at%20Island.mpg (animation of rainfall downwind of city) Greater rainfall shown downwind of Atlanta. Cities tend to create more rainfall downwind.

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Impact on Human health

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

Hot Air = Bad Air

Heat Wave Events per Year, 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?

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 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.

Urban trees intercept rainfall before it hits the ground 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 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.