Tag Archives: urban heat

Urban Heat Island Turns Top Floor Apartments into Ovens

It doesn’t matter where you live – extreme urban heat is a major problem and it’s getting worse.   As the effects of climate change take hold, temperatures are steadily rising – this year is on track to be the hottest on record and there’s no relief in sight for city-dwellers.   Especially those in poorer neighborhoods.

This article from the South China Morning Post about a recent study paints a grim picture for people living in older buildings.   Their homes get hotter and they spend a higher percentage of their income struggling to keep cool.

Low-income dwellers living on the top floors of old tenement buildings have become the forgotten victims of the urban heat island effect, a green group has found.

The heat – trapped in bare, unpainted concrete – dissipates into households below turning flats into “ovens”.

“The rooftops of some of these old buildings can get so hot you can fry eggs on them,” said Dr William Yu Yuen-ping, chief executive at the World Green Organisation, the group that carried out the study.

One measurement at Mong Kok one afternoon measured a maximum rooftop temperature of 74.4 degrees.   The air temperature in the flat below rose to 36.8 degrees, five degrees higher than the 32 degree mean temperature recorded by the Observatory that day.

Yu urged the government and the Commission on Poverty’s Community Care Fund to help these households by offering subsidies for planting rooftop gardens or painting buildings in white to dissipate heat.

Rooftop temperatures of 74.4 degrees Celsius – that’s 165.2 degrees Fahrenheit by the way.  And inside the top floor apartments… over 98 degrees Fahrenheit.   This problem is universal and white roofs can help lower the temperature, reduce energy consumption and save lives.

Study Links Climate Change to Hotter Urban Heat Islands

Cities are hot and getting hotter, thanks to global warming and the urban heat island effect.  With urbanization on the rise globally, extreme heat threatens human health, strains energy grids, and impacts global economies around the world.

Extreme heat is now ranked as the number one weather-related killer in the United States.  With over eighty percent of Americans now living in cities, urban heat islands and record high temperatures could cause serious health problems for hundreds of millions of people during the hottest months of the year.

Climate Central just released an analysis of government records for summer temperatures in 60 U.S. cities (1970 to date).  This study found that single-day heat island differences reached 27 degrees F in some cities, and that since 2004, at least 12 cities experienced 20 additional days a year above 90°F than surrounding rural areas.

This study also ranks the top ten urban heat islands in the United States.  Washington, DC ranks number 6 on this hit parade of urban heat.

Climate Central has prepared a useful interactive tool to help you learn more.

You can read more about the study here.

You can also read GCCA studies on heat health problems in Washington DC, and learn about strategies to lower urban temperatures and save lives.

Cool Roofs Studies are in the News

New reports from GCCA & ACEEE, and the Georgia Institute of Technology find that many cities are developing strategies to reduce excess urban heat, and that states, neighboring jurisdictions, utilities, and building owners are helping to mainstream these practices.

The first study comes from the Global Cool Cities Alliance (GCCA), and the American Council for an Energy Efficient Economy (ACEEE), in which they surveyed the policies of 26 North American cities.   E & E Publishing’s ClimateWire raised a few points we thought were worth noting, in Cities Take Steps to Address Extreme Heat

Several cities across the United States and Canada are now taking steps to mitigate local heat and prevent future warming, according to a new survey by the American Council for an Energy-Efficient Economy (ACEEE) and the Global Cool Cities Alliance (GCCA).  Of 26 medium and large cities, two-thirds cited extreme heat events and an increased number of high-heat days as the trigger for adopting policies to address the heat island effect.

. . .

Installing reflective and light-colored surfaces on walkways, roads and roofs is one of the most effective ways to address the heat island effect.  For instance, U.S. EPA research shows that conventional asphalt can reach 120-150 F in the summer, while reflective pavement stays 50-70 degrees cooler.

. . .

More than half of the 26 cities surveyed said they have requirements in place for reflective and vegetated roofing on private-sector buildings.  And nearly every city had policies to increase tree canopy and improve stormwater management.

ClimateWire also reported on a new study out of the Georgia Institute of Technology in which researchers looked at Phoenix, AZ, Philadelphia, PA and Atlanta, GA, and found that white roofs, reflective pavement and trees can counteract temperature increases in cities and save lives.   From Rising Temperatures Are Deadly, But Urban Cooling Fixes Can Counter Threats

[T]he researchers modeled how the three cities would respond to a minimum green space ratio on land parcels, setting a floor for areas covered with grass, gardens or trees. Vegetation tends to have a cooling effect by circulating moisture in the air that draws away heat during evaporation. Tree canopies also provide cooling shade.

The team also modeled how Phoenix, Philadelphia and Atlanta would behave with more reflective streets, sidewalks, parking lots and rooftops. Higher reflectivity, or albedo, means the area absorbs less sunlight, thereby lowering the temperature.

Stone and his collaborators then overlaid a health impact model. They found that combinations of increased vegetation and albedo could cut into projected increases in heat deaths, reducing them between 40 and 99 percent. “On average, we reduced the rate of increase by about 60 percent,” Stone said.

. . .

Groups like the Global Cool Cities Alliance are now trying to get cities to adopt these adaptation strategies, pitching them as a way to protect public health. However, it’s slow going, given that cities around the country address heat vulnerability differently, if at all.

You can find the full study HERE.

This report parallels a recent GCCA report, which looks at Baltimore MD, New York, NY, and Los Angeles, CA, and shows how reflective roofs and vegetation can cool air temperatures and save lives.

Note: Access to the ClimateWire articles is limited to subscribers.

Assessing the Health Impacts of Urban Heat Island Strategies in the District of Columbia

The District of Columbia is susceptible to extreme heat events whose health impacts are exacerbated by the fact that the city is often significantly warmer than surrounding rural areas during the summer. The study found that a 10-percentage point increase in urban surface reflectivity could reduce the number of deaths during heat events by an average of 6%. Adding a 10% increase vegetative cover to the increases in reflectivity yielded an average 7% reduction in mortality during heat events. During the decades between 1948 and 2011, an average of 285 people died of heat-related causes. A 6-7% decrease in mortality would save approximately 20 lives per decade. In addition, an even larger reduction would be expected in hospital admissions from heat-related illness, although this was not a specific finding of this analysis. Changes in temperature and humidity (as measured by dew point temperature) in both scenarios were relatively minor, yet were significant enough to contribute to the reduction of deaths.

The District, given its current policy landscape and development, could achieve the increases in reflectivity and vegetation used in this study. Increasing District-wide roof reflectivity by 10 percentage points is achievable by converting dark grey roofs to white roofs on approximately 25 percent of the District’s buildings. Assuming the average roof lasts 20 years, the District could achieve this with end-of-life roof replacements in slightly more than 5 years. Achieving the same increase in reflectivity for pavements would require the conversion of 50 percent of District pavements from dark asphalt to a slightly lighter option like grey concrete. A significantly smaller percentage of pavements would need to be converted if cool coatings were applied where feasible.

Get the full study on our Cool Roofs and Cool Pavements ToolKit here.