Abstract
We examined the cooling effect of rivers under the conditions where surface water existed and where the water disappeared by drought. The followings were main results. There were differences on the surface temperature of the bridge and air temperature within river channel; they were clearly lower than surroundings under the condition of surface water existence, which was not observed in drought condition. However, air temperature above the bridge tends to be always lower than that of surrounding area. This tendency was consistent regardless of the existence of surface water in the river. The reduction of air temperature above the bridge was often observed under the condition where wind direction matched the direction of stream and where the wind speed was high. The influence of low temperature above the rivers reached around the double of river width in the transverse direction.
