We have been examining the current and historical difference between urban and rural areas in the U.S. with respect to heating degree days (HDD) and cooling degree days (CDD). Urban areas tend to be warmer than rural areas due to the urban heat island (UHI) effect, i.e. the greater absorption of heat during the day by cement, asphalt and other building materials prevalent in urban areas, and the reradiation of that heat at night. Our goal is to estimate to what degree the UHI may be decreasing/increasing energy use for residential heating and cooling in urban areas over rural areas, and how any decrease/increase may be evolving with time.

We have examined daily minimum and maximum temperature measurements dating back to 1960 made at over 9,400 U.S. climate stations logged in NOAA’s Global Historical Climatology Network database. These records have been converted to HDD and CDD, summed by degree day type per annum, and separated into urban and rural categories based on the 2010 U.S. Census urban boundaries. Individual climate stations were then cross-referenced with regional housing characteristics such as average square footage, space heating fuel types, and air conditioning data from EIA’s 2005 Residential Energy Consumption Survey, as well as with recommended insulation levels for different climate zones as proposed by the U.S. Department of Energy.

At this point, these data have been used to model the total annual Btu requirements for residential space heating/cooling within the boundaries of the country’s 20 largest metropolitan areas (ca. 2010) as well as up to 50 miles beyond these boundaries into the outlying rural areas. Our modeling is being done using a range of insulation levels, furnace and air conditioner efficiencies, and duct efficiencies. We will present findings on how much faster temperatures are rising in urban vs. rural areas, and what effect this difference may be having on energy use and expenditures for residential heating and cooling inside and outside of the 20 largest U.S. metropolitan areas.