都市内河川が周辺の温熱環境に及ぼす効果に関する研究

Abstract

This paper describes the results of field observation about the micro-climate in and around the Ota River flowing through Hiroshima City. Meteorological elements - air temperature, humidity, wind direction and velocity were measured at several stationary points, moving around the river by automobile or bicycle, and moving on foot within the river section along the bridge. These observations were conducted in each season at two sites having different river width and structure (with floodplain or not). According to the vertical profiles of air temperature from the water surface to the bridge, the river is considered as the heat source in cooler seasons and as the heat sink in warmer seasons to the air within the river section. The appearance of the obvious difference between air temperature on the bridge and surrounding built-up area is restricted in warmer seasons. Namely, the river seemingly acts only as the heat sink to the adjacent field in urban area. The drop in air temperature above the river in warmer seasons is proportional to the surface temperature difference between river water and asphalt pavement, and is also affected by the direction and velocity of the wind. Above the floodplain, the air temperature decreases sooner than in surrounding built-up area after sunset, so it is a suitable place to get a comfortable feeling of the evening cool in summer. The results of detailed air temperature measurement at a height of 1.5m along the street, which lies at right angle to the river, show that the discernible reduction in air temperature may be spread to the extent about 150〜500 m from the river. However, the most variation in air temperature occurs within about 10 m from the edge of water.