DECADES WHAT THE TRENDS TELL US Sustainability: The Urban Heat Island By Sally Wittlinger Research Analyst Decision Center for a Desert City Arizona State University Q: What were the most interesting and important trends in Arizona sustainability that occurred in the previous decade? What is the significance of these trends and what insights can we apply to the new decade? A: In the first eight years of the past decade the population of the Phoenix metropolitan area increased from more than 3.25 million people in 2000 to more than 4.28 million people in 2008. During the mid-part of the decade, when the population growth rate was at its highest, the area was characterized by rapid development and urban sprawl. In addition, many highdensity residential developments were being added to the urban core. The result has been an intensification of the Urban Heat Island effect. The Urban Heat Island (UHI) is a phenomenon of higher nighttime temperatures in the urban core compared to the surrounding rural countryside. The UHI results from urbanization and replacing natural land surfaces with materials that retain heat and has resulted in a marked increase in the nighttime temperatures recorded at Phoenix Sky Harbor International Airport during the past decade. Number of Days with Minimum Temperature Greater than 90°F at Phoenix, Sky Harbor Airport 14 12 INDICATORS DECADES VOLUME 1 / ISSUE 10 JANUARY 2010 arizonaindicators.org Arizona Indicators is an online information resource and analysis tool that centralizes data about the state and its communities. Arizona Indicators presents interactive visualizations, clear data descriptions, and public opinion data in a broad range of content areas. This project is made possible by generous support from the Arizona Community Foundation and Arizona State University. For more information, contact Andrea Whitsett at (602) 496-0217 or andrea.whitsett@asu.edu. Days 10 8 6 Arizona Indicators is a project of Morrison Institute for Public Policy. 4 2 0 19 1948 1950 1952 1954 1956 1958 1960 1962 1964 1966 1968 1970 1972 1974 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 2098 2000 2002 2004 2006 2008 10 Throughout the entire decade of the 1990s, there were a total of eight days when the nighttime low temperature at the airport remained above 90 degrees; from 20002009 there were 50 such occurrences, with 12 such nights in 2003 and 10 in 2007. In addition, the average June low temperature at Sky Harbor Airport during the decade just ended was 2.85 degrees warmer than for the previous decade of the 1990s. ARIZONA Source: NOAA's National Climatic Data Center, Satellite and Information Service As the Phoenix metropolitan area continues to sprawl, the urban heat island will expand from the urban core further into suburban regions. Vegetation can help to maintain cooler night temperatures but requires large amounts of water, as does the production of energy that is required for air conditioning needs. In order for us to continue living in this desert city, development must be done in such a way that ensures the comfort of the city’s residents and considers the sustainability of our water and energy resources. 411 N Central Ave Suite 900 Phoenix, Arizona 85004-0692 (602) 496-0900 Main (602) 496-0964 Fax MorrisonInstitute.asu.edu