Numerical simulation of urban heat island effect by the WRF model with 4-km grid increment: An inter-comparison study between the urban canopy model and slab model

The present study applies the WRF model involving the single-layer urban canopy model (hereafter, WRF_UCM) to urban climate simulation of the Tokyo metropolitan area for August (2004-2007) and compare results to (a) observations, and (b) the WRF model involving the slab urban model (hereafter, WRF_SLAB). In this urban area, WRF_UCM accurately captures the observed monthly mean daytime and nocturnal UHI, whereas WRF_SLAB does not show a nocturnal UHI. Moreover, the observed diurnal variations of the surface air temperature for central Tokyo and Kumagaya, a nearby inland city, are reproduced well by WRF_UCM. However, WRF_SLAB exhibits both a 1-hr phase shift and a 6.2°C excess oscillation magnitude over observations. In addition, WRF_UCM accurately reproduces the frequency distribution of surface air temperatures, showing a maximum at 27°C, whereas WRF_SLAB produce a bimodal distribution, with double peaks at 23 and 33°C. Finally, WRF_UCM does a much better job than WRF_SLAB at modeling the relative humidity.