Below-Canopy Microclimate During Tropical Storm Isabel in Baltimore, MD
Gordon Heisler1, Richard Grant2, John Hom1, David Nowak1, Richard Pouyat1, Martin Schmidt3, Joanne Stubbs4, Joćo Vasconcelos5, and Ian Yesilonis4
1USDA Forest Service, 2Purdue University, 3McDonogh School, 4CUERE-UMBC, 5University of Lisbon
Abstract: Measurements for a study of soil temperatures and moisture in and near Baltimore are providing an opportunity to observe the influence of urban structures on microclimate at people height below urban canopies. In this poster, wind speeds (at the 2-m height) and air temperatures (at 1.5 m) at four below-canopy points are compared to conditions in the open at the BES (Baltimore Ecosystem Study) primary weather station at McDonogh School in Owings Mills (Rural Open) and at the Baltimore Washington (BWI) airport during 15 days that included the passage of the center of Tropical Storm Isabel about 140 km southwest of Baltimore. Comparisons are also made with air temperature at the Downtown Baltimore (DMH) ASOS station (Center City).
All of the below-canopy sites were decidedly influenced by trees. During Isabel's influence, hourly average wind speed at the Rural Open station reached 8 m s-1, while the below-canopy sites had average wind speeds of 2.8 m s-1 or less. Generally, urban canopies reduced gust speeds less than average speeds. Gust speeds reached 14.7 m s-1 at the Rural Open site and as much as 9 m s-1 at below-canopy sites. At these sites, trees rather than buildings were probably most responsible for the large reductions in wind speed. The generally warmest below-canopy site was at the City Center site, which was more than 3°C warmer than the Rural Open site during a day with clear skies and low wind speeds. The coolest site was a wooded area at McDonogh School (Woods), which was as much as 8°C cooler than the Center City site on a night when skies were clear (net radiation ~ -40 W m-2) and wind speeds low. With high winds and cloudy skies, temperature differences were small. Air temperatures at the Airport showed evidence of the effects of higher thermal mass and more impervious cover than at the Rural Open station. Wind speeds measured at 2 m above ground at the Rural Open site were usually similar to Airport wind speeds extrapolated from the 10-m measuring height to the 2-m height; this indicates the quite open character of the BES primary weather station site.