Evaluation of the Simple Urban Energy Balance Model Using Selected Data from 1-yr Flux Observations at Two Cities

摘要

The authors' objective was to apply the Simple Urban Energy Balance Model for Mesoscale Simulation (SUMM) to cities. Data were selected from 1-yr flux observations conducted at three sites in two cities: one site in Kugahara, Japan (Ku), and two sitesin Basel, Switzerland (Ul and U2). A simple vegetation scheme was implemented in SUMM to apply the model to vegetated cities, and the surface energy balance and radiative temperature T_R were evaluated. SUMM generally reproduced seasonal and diurnal trends of surface energy balance and T_R at Ku and U2, whereas relatively large errors were obtained for the daytime results of sensible heat flux Q_H and heat storage DELTAQ_S at Ul. Overall, daytime underestimations of Q_H and overestimations of DELTAQ_Sand T_R were common. These errors were partly induced by the poor parameterization of the natural logarithm of the ratio of roughness length for momentum to heat (kB~(-1)); that is, the observed kB~(-1) values at vegetated cities were smaller than the simulated values. The authors proposed a new equation for predicting this coefficient. This equation accounts for the existence of vegetation and improves the common errors described above. With the modified formula for kB~(-1), simulated net all-wave radiation and T_R agreed well with observed values, regardless of site and season. However, at Ul, simulated Q_H and DELTAQ_S were still overestimated and underestimated, respectively, relative to observed values.