Intraurban Differences of Surface Energy Fluxes in a Central European City

Abstract

Surface properties, such as roughness and vegetation, which vary both within and between urban areas, play a dominant role in determining surface?atmosphere energy exchanges. The turbulent heat flux partitioning is examined within a single urban area through measurements at four locations in ?ód?, Poland, during August 2002. The dominant surface cover (land use) at the sites was grass (airport), 1?3-story detached houses with trees (residential), large 2?4-story buildings (industrial), and 3?6-story buildings (downtown). However, vegetation, buildings, and other ?impervious? surface coverage vary within some of these sites on the scale of the turbulent flux measurements. Vegetation and building cover for ?ód? were determined from remotely sensed data and an existing database. A source-area model was then used to develop a lookup table to estimate surface cover fractions more accurately for individual measurements. Bowen ratios show an inverse relation with increasing vegetation cover both for a site and, more significant, between sites, as expected. Latent heat fluxes at the residential site were less dependent on short-term rainfall than at the grass site. Sensible heat fluxes were positively correlated with impervious surface cover and building intensity. These results are consistent with previous findings (focused mainly on differences between cities) and highlight the value of simple measures of land cover as predictors of spatial variations of urban climates both within and between urban areas.