Variations in the cooling effect of a small urban river depending on urban canyon geometry

Abstract

Urbanization and climate change make urban temperature increase. Rapidly increasing urban temperature creates problems for the urban environment. Therefore, urban planning and design should consider heat mitigation strategies to reduce the temperature. Many researchers have studied urban cool islands as the heat mitigation strategies. Among them, urban river is an important design factor to reduce heat in the surrounding areas through evaporation and transfer of sensible heat, which is called the river cooling effect. In this study, river cooling effect includes its intensity and distance. River cooling intensity means the air temperature difference between river and urban, and river cooling distance means the diffusion distance of cool river air. Previous studies have found out river characteristics and climate influenced on river cooling effect. However, Urban canyon geometry near rivers, which is an important factor influencing the river cooling effect, has been overlooked so far. In this study, I evaluated the influence of urban canyon geometry on the river cooling effect. I measured the air temperature near Cheonggye stream and calculated the river cooling effect for 8 streets with different urban canyon geometry at 2 p.m. and 10 p.m. Street width and building height were selected as the urban canyon geometry. Mobile survey used for measuring air temperature. This method could make densely measured points from river to urban area. The results show that the average river cooling intensity at 2 p.m. is 0.52 ℃ and larger than 10 p.m. the river cooling distance, however, is similar to 10 p.m. as 24 m. Also, the results indicate that street width and building height affect the river cooling intensity and the river cooling distance of Cheonggye stream. This relationship is shown in the daytime. During a day, the river cooling effect increases as streets get narrower and building heights get lower. This study is important to evaluate river cooling effect analysis in micro scale and find out basic characteristic of urban canyon geometry to make river cooling effect larger. Our finding can help urban planning and design near the river for mitigating urban warming.