Hydrometeorological variability in the Korean Han River Basin and its sub-watersheds during different El Nio phases

This study investigated the characteristic changes in precipitation and runoff that occur in the Korean Han River Basin and its sub-basins in association with the cold-tongue (CT) and warm-pool (WP) El Nio phases during spring and summer. During the WP El Nio years, rainfall in spring and its coefficient of variation were higher than long-term normal precipitation. During the CT El Nio years, summers tended to be drier than in climatologically normal years, although the variability in precipitation during the summer was relatively lower. The data for runoff showed wetter springs compared to long-term normal years during both types of El Nio events and significant changes in runoff during summer under CT El Nio conditions. During the WP El Nio years, increased runoff was seen for 95.8 % of all basins and this increase was statistically significant for 58.3 % of these basins, but variability in runoff was small. Overall, the findings confirm that water resources in the Han River Basin during the spring and summer are sensitive to CT/WP El Nio events. Thus, for basins such as these, where seasonal variability and the uncertainty of hydrologic data are high, investigation of the relationship between climatic factors and hydrologic parameters is necessary to maintain the stability of the water supply system and to allow prediction for water resources.