After the full urbanization of the Seoul during the late 1980s several new towns where established outside the Greenbelt. Several push-and-pull factors have followed and influenced the rapid urbanization of the capital region of Korea. Currently more than 23 Million inhabitants are living in the Seoul Metropolitan Area (SMA). This has become one of the biggest urban agglomerations in the world. The greenbelt has had a significant impact on the whole of the SMA. Due to the containment by the greenbelt, an intensive urbanization has occurred within the constrained Seoul City. This has resulted in a limited number of green areas and water bodies in the Seoul. The number of green spaces per inhabitant is one of the lowest in the world. Next to the 600m wide Han-River that flows from east to west through the central part of the city, there are no open streams or water bodies. Therefore, the establishment of new green or water bodies in the Seoul City is of great importance. One of the most remarkable projects is the redevelopment of a 5.84 km long and 24 m wide two-tier expressway to a river stream.
The authors investigated the micro-climate changes and urban-scale cooling load reduction which has resulted from the so called Cheonggyecheon water stream. This stream is located in central Seoul and runs from the northern central business district into the Han-River. After the Korean war (1950-1953) the Cheonggyecheon river was for more than 50 years covered with pavement and concrete overpass structures. The reconstruction of the expressway was carried out from 2002 to 2005. To estimate the thermal impact of the expressway into a water pathway remote sensing analysis (Landsat 7 ETM+) was undertaken. 20 Landsat-7 ETM+ images from 2000 till 2012 were used to compare the land surface temperature (LST) distribution during the time the expressway was there and through to the reconstruction and the establishment of the river stream. A built-up area of two km width surrounds the new water pathway and this was used as a reference area. The investigation could show that the establishment of the Cheonggyecheon stream forced a considerable thermal impact, i. e. an average decrease in the land surface temperature by seven degrees Celsius.
The results indicate that the cooling benefits of the restored stream areas are promising in the locations.