Study of the effects of a river on the thermal environment in an urban area

Abstract

This paper describes the results of field observations on the micro-climate in an around the Ota River flowing through Hiroshima City. At first, detailed measurements of temperature distribution within the river section were carried out along the bridge. Then, both the horizontal and vertical extent of a thermal river-effect were confirmed by moving observations along the streets crossing the river and by simultaneous balloon observations above the river and in the downtown area. In addition to these short-term observations on fine days, long-term temperature measurements were conducted at several stationary points in and around the river during 14 months. The drop in air temperature above the river exceeds 5°C on fine days in warmer seasons, and is proportional to the surface temperature difference between the river water and the asphalt pavement. These thermal effects were discernible at least a few hundreds meters horizontally and more than 80m vertically. However, temperatures were also affected by the building density and wind direction and velocity.