Institute of Ecosystem Studies

2007 BES Annual Meeting Presentation and Poster Abstracts

Mapping Baltimore-Area Air Temperatures
Heisler, Gordon
Co-Authors: Gordon Heisler, Jeffrey Walton, Ian Yesilonis, David Nowak, Sue Grimmond, Richard Pouyat, Karla Hyde, Michelle Bunny, Eric Greenfield, Andrew Lee, John Hom
Abstract: We began continuous measurements of air temperature at the 1.5-m height at five sites near Baltimore in June 2003. These sites are in a large open pasture, a woodlot near the pasture, a residential area with tree cover and single-family houses, a lawn area with nearby trees between two large apartment complexes, and a residential area with some trees and large lawn areas. Temperature data are also available from National Weather Service (NWS) sites in downtown Baltimore and at the Baltimore/Washington International Airport. We hypothesized that we could use data from these sites to develop mathematical models to describe air temperature difference, dT, between one of these sites as a reference and the other sites. The model would use differences in upwind tree, impervious, and water cover as predictor variables. This paper illustrates a test of that hypothesis. We expect the results to be useful for evaluating urban structural and vegetation influences on air temperature for other studies related to human thermal comfort, carbon cycling, soil and stream temperatures, ozone formation, and effects of UV radiation for human health. Maps and computer graphics based on the resulting model will help to convey urban climate dynamics to the public. The downtown NWS site served as the reference point for the hourly values of dT. The model was developed by regression analysis to relate dT to the predictor variables, which in addition to land cover included wind speed, cloud cover, humidity, antecedent precipitation, and descriptors of topography. The figure shows the pattern of predicted temperature differences across the Baltimore area for one daytime hour, when temperature differences are usually small, contrasted with one nighttime hour when temperature differences are large. The figure also depicts the effect of elevation on the temperature.
Predicted temperature differences across Baltimore and vicinity at 3:00 PM (15:00) and 10:00 PM (22:00) on June 20, 2004. The National Weather Service station at the Baltimore Science Center (triangle with dot) serves as the reference temperature. Darker yellow to orange areas are a little warmer, negative values (greens and blues) cooler. Maps on the left included the predicted effect of elevation; those on the right are without the elevation effect and show the effect of tree, impervious, and water cover only. Symbols at the top of the maps show that 3:00 PM wind was from the southwest at about 5 knots and clouds were scattered. At 10 PM, wind was calm and skies were clear, conditions conducive to development of large temperature differences between rural and urban locations.