Risk assessments of outdoor hot environment using urban meteorological numerical model system

In Japan, patients of heat disorder, who are carried by ambulance, intend to increase due to the air-temperature rise. Hence, a prediction of heat disorder is widely informed by meteorological information services and public organizations. The WBGT (Wet-Bulb Globe Temperature), which is well known as a heat disorder index, is often used for predictions. Although the heat disorder (WBGT) prediction and its information release are carried out for each prefecture of Japan, those should be done for urban district scale because of a strong influence of the local-scale outdoor environment on the heat disorder. Therefore, we tried to risk assessments of the heat disorder, using an urban meteorological and building energy model system. This model can resolve an urban district scale with canopy meteorology and air-conditioning waste heat. Adding the source programs calculating WBGT, PMV (Predicted Mean Vote), PPD (Predicted Percentage of Dissatisfied), and SET* (Standard Effective Temperature) to the model system, these outdoor thermal sensation indexes are outputted. First, the model verification was conducted by comparison with the meteorological observation data. The observations were carried out during the period of August 6 to 14 in 2007 at commercial, residential, and green park areas. A very hot condition appeared everyday during this period with the daily maximum temperatures exceeding 33 deg.C. For hourly WBGT data, at the all district (commercial, residential, and green space areas), the numerical model was able to reproduce the WBGT conditions of more than 60% for the measured WBGTs of 25~28 deg.C corresponding to the “alert” rank. Moreover, the model reproduced the WBGT condition of 65.7%, 59.7%, and 75.8% for the measured WBGTs of 28~31 deg.C corresponding the “sever alert” rank. Consequently, our model system can be utilized for risk assessment of outdoor heat disorder. Secondly, a risk assessment of heat disorder was conducted for many model meshes in Osaka City, Japan. For 262 meshes, the averaged district structure, main building type, averaged green coverage and so on were estimated from the Osaka GIS data. A numerical simulation was conducted from July 20 to August 30 in 2007. As a partial result, exposed hours of the “severe alert” rank at commercial and office building meshes in the center of Osaka City were shorter while those at the surrounding residential housing meshes were longer. Additionally, we tried to estimate a heat disorder risk from use of the number of heat disorder patients carried by ambulance. From this analysis, maps of the heat disorder risk were produced by the model calculations. The risk distribution was clearly different from the geographical distribution of daily maximum temperature.