Relationships between aerodynamic roughness and land use and land cover in Baltimore, Maryland

Abstract

Urbanization changes the radiative, thermal, hydrologic, and aerodynamic properties of the Earth's surface. Knowl­ edge of these surface characteristics, therefore, is essential to urban climate analysis. Aerodynamic or surface rough­ ness of urban areas is not well documented, however, be­ cause of practical constraints in measuring the wind profile in the presence of large buildings. Using an empirical method designed by Lettau, and an analysis of variance of surface roughness values calculated for 324 samples averaging 0.8 hectare (ha) of land use and land cover sample in Balti­ more, Md., a strong statistical relation was found between aerodynamic roughness and urban land use and land cover types. Assessment of three land use and land cover systems indicates that some of these types have significantly different surface roughness characteristics. The tests further indicate that statistically significant differences exist in estimated surface roughness values when categories (classes) from dif­ ferent land use and land cover classification systems are used as surrogates. A Level III extension of the U.S. Geo­ logical Survey Level II land use and land cover classification system provided the most reliable results. An evaluation of the physical association between the aerodynamic properties of land use and land cover and the surface climate by nu­ merical simulation of the surface energy balance indicates that changes in surface roughness within the range of values typical of the Level III categories induce important changes in the surface climate.