The importance of including anthropogenic heating in mesoscale modeling of the urban heat island

The surface characteristics and anthropogenic activities in the urban environment often lead to local warming relative to the rural surroundings – a phenomenon known as the Urban Heat Island (UHI). The UHI is typically largest during evening hours and during the winter. Nevertheless, the UHI effect in summer can be of particular interest with respect to its impact on urban air quality, air conditioning energy demand, human comfort, and heat-related illness. The urban-rural differences in albedo, moisture, roughness, and thermal capacitance are often cited as the key causes for the urban heat island. Studies that focus on the role that these parameters play in the development of the UHI are common (e.g., Carlson and Arthur, 2000; Hafner and Kidder, 1999; Owen et al., 1998; Taha et al., 1991). Anthropogenic heating is also a potential factor in the urban heat island, but is often dismissed under the assumption that it is relatively small in magnitude. While it is true that anthropogenic heating is small compared with summertime mid-day solar insolation, it plays a major role in the surface energy balance at times when the urban heat island effect is at its maximum (night time and winter). Recent studies suggest that anthropogenic heating, in fact, may be a significant contributor to the UHI (Fujino et al., 1996; Ichinose, 1999; Sailor, 2003). Additional studies are needed, however, to quantify the role of anthropogenic heating in the urban climate, and provide guidance with respect to the value of including it as a source term in modeling efforts. This serves as the motivation for the present work.