The present study describes essential features of the local weather when heavy rainfalls occur in the Tokyo metropolitan area. Case study was carried out in detail for the two heavy rainfall events: August 2 2002 (Case 1) and August 10 2004 (Case 2). The following characteristics are found. (a) The atmospheric stability was low while Japan Island was covered with Pacific high for both cases. (b) In the Case 1, the E-S type wind system was observed and surface winds from the Kashima bay, Tokyo bay, and Sagami bay converged in Tokyo during the several hours before heavy rainfalls occurred. (c) Additionally, it was found that the cold outflows enhanced the convergence. (d) On the other hand, such a convergence was not found in the Case 2, which causes the convective rainfalls quickly decreased.

For quantitative evaluation of the effect of water sprinkling as a mitigating method of urban “Heat Island”, a comprehensive numerical model is proposed. The developed model describes both air-water-vapor movement and heat transport in atmosphere and subsurface, by using the generalized concept of multi-phase, multi-component solid-fluid system. It includes hydrodynamic phenomena, such as pseudo static air flow in atmospheric boundary layer, the heat balance of solar radiation and long-wave radiation, evaporation, transient heat transfer among the solid, liquid and gas phases. In order to confirm the performance of the model, several case studies have been made regarding the basic modeled processes. The calculated results are reasonable and consistent with the analytical solutions and/or laboratory experiment with the reasonable parameters.

By applying the Atmosphere-Surface-Coupled, Hydrothermal Environment Model, the reproducibility of the field experiment of water sprinkling is examined.
Firstly, making a 2-D vertical model which includes atmosphere and subsurface regions, and inputting the meteorological data (atmosphere temperature, wind velocity, relative humidity and solar radiation) of the experimental site, the hydrothermal parameters of the model are identified by matching the calculated with the observed surface and subsurface temperatures at un-sprinkled condition. Then, giving water volume on the surface layer of the model at water sprinkling, the changes of environment near water sprinkled area are simulated. As the results, the atmosphere, surface and subsurface temperatures observed from daytime to the following morning are preferably reproduced by the model.

Simultaneous observation of air temperatures was carried out inside and outside of the city park (Takashi Ryokuchi) in the central area of the Toyohashi city to estimate “cool island intensity” defined as temperature difference between the park and residential areas, and evaluate the effect of cold air advection or drainage from the city park. Observation period is Jul. 30 to Aug. 30 and the number of observation points was 29. Observation results show that the averaged cool island intensity was -0.84°C during the observation period. The cooling effect of Takashi Ryokuchi on the surroundings (residential area) in calm condition was small compared with that in windy condition.

The aim of this paper is the design of water permeable/retainable porous paving bricks for controlling the urban heat island phenomenon. The model porous bricks, which had 22-43% open porosity and 0.4-50μm of average pore size, were prepared by sintering using cubic-shape fly-ash powders with very narrow particle size distributions. Influence of pore sizes and porosities in the model bricks on water pump-up ability, coefficient of permeability, water vapor evaporation ability and evaporation cooling effect of the brick surface temperature were evaluated quantitatively. The brick which had 33% or more of porosity and 4-30μm of average pore size was considered to be the most suitable for water permeable/retainable porous paving bricks.

We propose a new approach to derive a spatially-averaged transport equation for a scalar quantity, such as temperature or concentration, for an urban canopy model. First, in order to mathematically describe the actual momentum field as a completely continuous field, the underling concepts of the immersed boundary method are employed, where we assume that (i) the entire simulation space is filled with a fluid, and (ii) an external body force field exists that reduces the wind speed to zero at all positions coinciding with the space occupied by the buildings. Second, we mathematically describe the field of a scalar quantity as a completely continuous field by introducing a source/sink field that acts only inside the space occupied by the buildings and controls the values of the scalar quantity at the acting points. Then, we obtain a spatially-averaged scalar transport equation by applying a (solid-inclusive) spatial averaging operation to the governing equation for the scalar field. Finally, by assuming that the source/sink field controls the spatial-average of the scalar quantity inside the buildings to be equal to that outside the buildings, we can obtain a spatially-averaged scalar transport equation that has no undefined term in the case the boundary of the averaging cell does not cross the space occupied by buildings.