Impact of land-use changes on stream runoff in Jeju Island, Korea

Jeju Island, the region with the highest level of rainfall in Korea, is formed by vesicular volcanic rocks and ash causing half of the total rainfall to permeate underground, which gives the Island rich groundwater resources, although most of the streams are dried. The expansion of agricultural land and the massive establishment of tourist development and road construction in the lower area of the streams increase the damage occurring near the lower area of the streams. To achieve the important integration of Jeju Island’s water resources, a stable water supply from surface water is needed along with preserving and managing of the groundwater. The changes in the stream flow amount due to prolonged land-cover need to be understood by creating and using a map for rational development and utilization. In this study, the four major streams in Jeju Island were selected for the hydrologic analysis by the The Soil and Water Assessment Tool (SWAT) model according to the change in land use. A land use data from 1975 to 2000 from landsat satellite images provided by the Ministry of Environment and Arcview program was used. Due to the change in land-coverage in four major streams between the past and the present, the areas of impermeable land in the lower area of the streams were generally extended approximately two times higher than in the past. Accordingly, it was proved that the amount of direct runoff has been increasing by at least 1 to 6%. Especially, in the lower part of Oaedo stream, the increase in surface discharge was highest. The quantitative hydrological analysis due to land use change by SWAT model is thought to be a good approach for identifying the impact of land use in Jeju island.  Key words: Jeju Island, soil and water assessment tool (SWAT), land use change, stream runoff.