Does the restoration of an inner-city stream in Seoul affect local climate?

Urban climate changes associated with the restoration of an inner-city stream in Seoul, Korea, are investigated using observational data. The stream, called the Cheonggye stream, which had been hidden and covered with cement/asphalt for 46 years, runs 5.8 km eastward through a central region of Seoul. Intensive observations were made in the stream area for a number of summertime periods before, during, and after the stream restoration to detect the effects of the stream on its nearby climate and to quantify them. It is found that after the stream restoration the near-surface temperature averaged over the stream area dropped by 0.4oC, with the largest local temperature drop being 0.9oC. The stream effect on air temperature is also evident in the temperature distribution along a street traversing the stream. In the daytime after the stream restoration, the sensible heat flux was greatly reduced and the ratio of sensible heat flux to net radiative flux dramatically decreased. It is found that in the stream canyon the along-stream flows can be dominant even when the ambient wind direction is not principally in the along-stream direction and that the wind speed is weaker than the ambient wind speed. These first-time results of the restored-stream effects on urban climate could contribute to the scientific basis of urban planning which aims to make a large city comfortable to live in and nature- and environment-friendly.