In recent years, localized heavy rainfall events over urban areas have caused severe damage in Japan. Although localized heavy rainfall events produce low total rainfall amount, they can produce very intense rainfall in a limited area and in a short time period. Intense rainfall in urban river basins with small catchments and impervious land cover can cause inundation of areas inside levees and increase river channel and drainage pipe water levels rapidly. For example, the severe localized heavy rainfall that occurred near Zoshigaya, Tokyo, on 5 August 2008, caused a rapid increase in discharge and killed five people working in a drainage pipe.
 To improve the skill of numerical weather prediction, considerable efforts have been made to data assimilation to improve the initial conditions of numerical forecast models [e.g., Kawabata et al., 2007]. Urban canopy models used in cloud-resolving models are also being improved [e.g., Tanaka and Ikebuchi, 1994; Kusaka et al., 2001; Kusaka and Kimura, 2004; Tanaka, 2004; Kanda et al., 2005; Lei et al., 2008].
 Pielke et al. [2007, 2011] indicated that the urbanization is one of the important issues for the impacts of land use and land cover on local, mesoscale, and regional climate, including rainfall. The Metropolitan Meteorological Experiment conducted in St. Louis, MO, USA, in 1970, showed that urban conditions led to increased precipitation during summer [e.g., Changnon and Huff, 1986; Shepherd, 2005]. Shepherd and Burian  indicated that rainfall has increased downwind of Houston, Texas, using data derived from the precipitation radar onboard the Tropical Rainfall Measuring Mission. Niyogi et al.  indicated that thunderstorms occurred more frequently over Indianapolis, IN, USA, than over a rural area based on an analysis of the radar-based climatology of 91 summertime thunderstorm cases from 2000 to 2009. Kishtawal et al.  found that the increasing trend in the frequency of observed heavy rainfall events over Indian monsoon region is more likely in regions where the pace of urbanization is faster, by using in situ and satellite-based precipitation and population data sets. In the Tokyo metropolitan area, Japan, observational studies have also suggested that the urbanization affects summer rainfall, including localized heavy rainfall. In an analysis of 16 year Automated Meteorological Data Acquisition System (AMeDAS) rain gage data, Fujibe  found a positive precipitation anomaly related to the urban effect over the central and inland areas of Tokyo. Sato et al.  found that the precipitation frequency in the metropolitan area in and around Tokyo was remarkably higher than that in the surrounding areas based on an analysis of 12 year radar data.
 Some researchers have attempted to investigate the effect of urban areas on localized heavy rainfall based on numerical model experiments. Gero and Pitman  reported that the size of the urban area on the western plain of central Taiwan affected the location of thunderstorms and precipitation. Shem and Shepherd  indicated that the existence of urban areas contributed to the intensification of convective rainfall systems in two rainfall events over Atlanta, GA, USA. Shepherd et al.  indicated that future growth of urban land cover could cause an expansion of heavy rainfall area over Houston, Texas. Niyogi et al.  showed that a typical storm over Indianapolis was greatly affected by the existence of an urban area.
 Focusing on the Tokyo metropolitan area, Kanda et al.  carried out numerical simulations for a cumulus cloud line over a major street in Tokyo under summer conditions and showed that the cloud line weakened and shifted toward a suburban area without urban heating. Moteki et al.  found that the existence of the urban area intensified a convective rainfall event occurred in Tokyo in 1999. Matheson and Ashie  identified different urban effects on precipitation based on numerical experiments for several rainfall events in Tokyo.
 Although the impact of the urban heat island on precipitation over and leeward and windward of cities has been studied using numerical models, most of them have focused mainly on the existence of a city, based on sensitivity experiments with the city artificially replaced by grassland or forest. The influences of urban areas on the urban heat island and precipitation include the effects of anthropogenic heat, artificial land cover, and three-dimensional urban geometry [e.g., Ryu and Baik, 2012]. To appropriately improve numerical weather predictions and apply the results to mitigation policies in urban planning, the impacts of urban on both momentum exchange and heat transfer need to be assessed separately. In addition, there is a need to understand how individual components of the urban environment may affect precipitation.
 Urban environmental components that may affect heat transfer include anthropogenic heat from devices, such as air conditioners and automobiles, and artificial land cover, such as asphalt. Particularly, artificial changes in land cover and land use simultaneously modify momentum transfer. So far, few studies have attempted to understand the individual effects of artificial land cover and anthropogenic heat on precipitation in urban areas. Artificial land cover on one hand suppresses surface evaporation and on the other hand converts incoming solar energy to surface sensible heat.
 With the aforementioned considerations, in this study we conducted ensemble experiments using a cloud-resolving model to assess the individual effects of artificial land cover and anthropogenic heat on a localized heavy rainfall event that occurred over Zoshigaya in Tokyo in 2008. The rest of the paper is organized as follows. The next section describes the numerical model used and the design of numerical experiments. The results are presented and discussed in section 3. Main conclusions are given in the last section.