The energy budget of the urban surface: two locations in Dublin

Abstract

Urban areas generate distinctive climates that are revealed in the statistics of wind, temperature, humidity and so on. These properties are the result of energy exchanges between the atmosphere and underlying urban surface, which is the focus of physical climatology studies. These exchanges form an energy budget (EB), which includes radiation exchanges (both solar and terrestrial), the turbulent fluxes of sensible and latent heat and the energy transferred to the substrate by conduction. An evaluation of these exchanges and their spatial variation is essential to explaining the effect that cities have on climate at all scales. However, observing these exchanges is difficult and requires both sensitive equipment and careful placement to ensure representative readings. This paper presents some initial results on the EB over two urban surfaces in Dublin, one a densely built urban site near the city centre and the other a mature, well vegetated, suburban site. The results demonstrate the effects of different urban surface features on surface-air exchanges. The objective hysteresis model is also employed to evaluate the energy balance residual. Results show good agreement between modelled and residual values. Although there have been studies on Dublin’s urban climate, most notably its urban heat island (UHI), there has been no prior study of the energetic processes responsible for this local climate change. This research programme, for which initial results are presented in this paper, is one of the few studies globally that will maintain long-term measurements (five years) of urban EBs.