Atmospheric changes in a growing community (the Columbia, Maryland experience)

Abstract

An account of seven years of meteorological observations in the growing town of Columbia, Howard County, Maryland, in the Baltimore-Washington corridor is given. Information was collected from fixed stations and mobile surveys. In the interval from 1968 to 1975 the town grew from 200 to 20000 inhabitants, with building activity eliminating the original diversified rural microclimates. An unmistakable urban heat island has developed that is quite notable nocturnally when it maximally reaches 8° C in the densely built-up town center. The time series of the maximal heat island is linearly related to the logarithm of population figure. At midday on sunny days the IR surface temperatures are directly proportional to the per cent of area built-up. The radiation balance reflects the changes in the urbanized area. There is little heat loss from evapotranspiration but large heat transport into the surface (day) and out of the surface (night). No effect on precipitation is (as yet) discernible. Relative humidities are lower in the town area than in the rural district. Roughness has increased and wind speeds have been reduced. In all seasons, except summer, hours of turbulent wind have decreased. Run-off has become typically urban and air pollution has increased (presumably from motor vehicle traffic). All findings support earlier studies on town climate and reveal considerable detail on the progress of atmospheric modification in the urbanization process.