Thermal differentiation of "local climate zones" using temperature observations from urban and rural field sites

In a recent study on method and communication in observational heat island literature, “completeness of reporting” was cited as one of several critical weaknesses. This weakness was attributed to the lack of site metadata reported in heat island literature. We have therefore developed “local climate zones” (LCZ) to simplify and standardize the description of urban climate field sites. LCZs are defined as regions of uniform surface geometry and cover, and are therefore believed to have relatively homogeneous surface thermal climates. Until now, however, this assumption has not been tested with empirical temperature data from actual urban and rural field sites. In this paper, we present temperature observations from selected LCZs in three representative locations: a small East Asian town (Obuse, Japan), a medium-sized European city (Uppsala, Sweden), and a large North American city (Vancouver, Canada). Results show that significant temperature differences exist across the hierarchy of LCZs, and that these differences generally support the current structural division of the LCZ system. During calm and clear evenings, screen-height temperature differences vary with the degree of structural separation between zones. As expected, temperature differences between zones of large separation can reach 10°C. More noteworthy is that between zones of similar structure, differences are reduced but still significant, averaging 1–3°C. These results highlight the potential application and geographic appeal of LCZs in urban climatology. While we anticipate a broad range of uses for LCZs, their most effective use will be in reporting urban microclimates and canopy-layer heat islands.