Friday, June 20, 2014

Cities Are Heat Islands - Mitigation is Possible

A survey of North American cities by the American Council for an Energy Efficient Economy (ACEEE) and the Global Cool Cities Alliance (GCCA) finds that confronting the challenges of extreme weather, adapting to a changing climate, and improving the health and resiliency of urban populations are driving cities to develop and implement strategies to reduce excess urban heat.

Nearly two thirds of the cities surveyed cited local extreme weather events as a key reason for initiating urban heat island mitigation strategies. U.S. cities are waking up to the growing threat of urban heat and employing a number of innovative approaches suited to their location and priorities," said ACEEE researcher and report author Virginia Hewitt

ACEEE and GCCA surveyed 26 cities in the U.S. and Canada representing all of the major climate zones, geographies, and city sizes. Despite the diversity of the respondents, several common themes emerged.

Local governments are "leading by example" by requiring use of "cool" technologies, such as reflective roofs on municipal buildings, lining city streets with shade trees, and raising public awareness.

Additionally, more than half of the cities have some kind of requirement in place for reflective and vegetated roofing for private sector buildings. Almost every city had policies to increase tree canopy and manage storm water.

"Our report finds that by addressing their urban heat islands, cities are more effectively delivering core public health and safety services, making them attractive places to live, work, and play," said Kurt Shickman, executive director of the Global Cool Cities Alliance.

The report includes case studies on how several cities have responded to urban heat, demonstrating the variety of strategies employed. In response to a study that found that Houston's roofs and pavements can reach 160° °F, the city now requires most flat roofs in the city to be reflective. Washington D.C. has instituted a wide suite of programs such as Green Alleys, which helps residents manage excess stormwater by replacing pavement with grass and trees, and requiring reflective roofs on all new buildings.

The survey also found that most city governments are not acting alone to reduce excess heat. States, neighboring jurisdictions, utilities, developers, contractors, and local building owners are collaborating to create incentives for communities to reduce urban heat and mainstream these practices.

Cities surveyed in the report include: Albuquerque, NM; Atlanta, GA; Austin, TX
Dallas, TX; Houston, TX; Las Vegas, NV; Los Angeles, CA; Louisville, KY; New Orleans, LA; Phoenix, AZ; Sacramento, CA.

Many of these are broadly similar to north Australia in summer, especially those in the SW of the USA.  With climate modelling for Australia predicting major heat issues in north Australia in coming years that will impact on living in the region it is prudent to examine options that will minimise the heat island effects.

A recent scientific journal article clearly showed a 2C effect now in the city of Phoenix in Arizona caused from night time use of air conditioners, and the heat emanated as waste heat was the cause.

What are we now doing here in Darwin?  Yes, we do have vegetation, but there has been little use of reflective roof coatings to mitigate heat gain, nor little use of green roofs.

And nothing seems to have been mandated in building codes for this region, a location where it is always hot, and buildings need cooling [never heating!].

Cool Policies for Cool Cities: Best Practices for Mitigating Urban Heat Islands in North American Cities, visit:

 The survey is available on the Cool Roofs and Pavements Toolkit:

NOTE - The Global Cool Cities Alliance is a non-profit organization works with cities, national governments, and other stakeholders to advance policies and actions that reduce excess urban heat in order to cool buildings, cool cities, and to mitigate the effects of climate change through global cooling.

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