A major problem in urban climate modeling is determining how the heat fluxes from various canyon surfaces are affected by canyon flow. To address this problem, we developed a water evaporation method involving filter paper to study the distribution of the convective transfer velocity in urban street canyons. For 3D cubic arrays, the relation to canyon aspect ratio was largely different from that of 2D canyon. And, as a case study, the variation of wind direction was investigated for some city-like setting. The area-averaged transfer velocity was insensitive to wind direction but its local deviation was significant. In addition, we measured the transfer velocity for a clustered block array surrounded by relatively wide streets. The effect of spatial heterogeneity on the transfer velocity was significant. Moreover, for a fixed total building volume, the transfer velocity was considerably larger when the building height varied, than when it was uniform. Therefore, the water evaporation method with filter paper is expected to be useful for studying the transfer velocity and ventilation rates in urban areas with various canyon shapes.
