Theor. Appl. Climatol. 84, 35–45 (2006) DOI 10.1007/s00704-005-0142-3 Centre National de Recherches M et eorologiques, Toulouse, France Urban surface modeling and the meso-scale impact of cities V. Masson With 2 Figures Received February 4, 2004; revised April 12, 2004; accepted February 5, 2005 Published online September 26, 2005 # Springer-Verlag 2005 Summary New developments of the international community in modeling the urban canopy surface energy balance are presented and classified into five main categories: (i) models statistically fit to observations, (ii) and (iii) modified veg- etation schemes with or without drag terms in the canopy, and (iv) and (v), new urban canopy schemes, that present both horizontal and vertical surfaces, again with or without a drag approach. The advantages and disadvantages of each type of model are explained. In general, the more the phys- ics are correctly simulated, the more complex are the urban phenomenon that can be addressed, on the other hand however, the more consuming of computer-time and difficult to couple with atmospheric models the scheme becomes. Present use of these new models in meso-scale atmo- spheric models show their ability to reproduce the phenom- enon of the urban heat island (UHI) and some of its consequences – urban breezes, storm initiation, interaction with sea-breeze. Their use opens up new perspectives, for example in the mitigation of the UHI, or assessment of the role of air-conditioning systems or the impact of urban dynamics on air pollution. However, there is need to validate further the different urban models available. In particular it is necessary to com- pare model output with urban surface energy balance mea- surements. An intercomparison exercise involving these urban schemes is suggested as an efficient way to assess and improve these models. 1. Introduction: the urban surface While cities occupy only 0.05% of the Earth’s surface, more than half of the World’s inhabitants now live in urban areas, and are therefore sensi- tive to their environmental conditions. Among them, the cities’ climate is of importance, and differs from the climate of the adjacent country- side, due to the special nature of urban areas. The most well known atmospheric effect of towns on the atmosphere is the urban heat island (UHI): at night, city air is usually warmer by 3–10 K (Oke, 1987). This effect has economic consequences, but also an impact on human health, as has been shown by the excess mortality of 15,000 people in France during the heat wave of summer 2003, especially in the largest agglomerations (H emon and Jougla, 2003). Cities also generate other atmospheric changes, including effects due to the large rough- ness (e.g. Grimmond et al., 1998) such as changes to turbulence (for a review see Roth, 2000), en- hancement of storms (Bornstein and Lin, 2000), altered urban hydrology (Grimmond et al., 1986; Grimmond and Oke, 1986), and impacts on pollutant dispersion from streets into the atmo- spheric boundary layer, and their chemical evo- lution or radiative impacts. In particular, the pollution issue has led to several major experi- mental campaigns, such as METROMEX over St-Louis (Changnon, 1978), MEDCAPHOT- TRACE over Athens (Klemm, 1995), ESQUIF and ESCOMPTE over Paris and Marseille (Menut et al., 2000; Cros et al., 2003). Modeling can be a