Characteristics and controlling factors of the drought runoff coefficient

Abstract. Increasing water demand due to population growth and economic development or changes in rainfall pattern as a result of climate change is likely to alter the duration and magnitude of droughts. To establish sustainable water resource management based on changes in future drought risk, understanding the relationship between low-flow conditions and controlling factors relative to drought magnitude is important. This study is the first attempt at revealing the relationship between low-flow and controlling factors at differing drought severities. I calculated the drought runoff coefficient for six types of occurrence probability based on past observation data of minimum flow and precipitation. Furthermore, I investigated the pattern of change in the drought runoff coefficient in accordance with the occurrence probability and relationship between the coefficient and geological, land use, and topographical factors. The drought runoff coefficient for multiple drought magnitudes exhibited three behavior types corresponding to precipitation pattern. The results from a generalized linear model (GLM) revealed that the controlling factors differ depending on drought magnitude. In high-frequency drought, the drought runoff coefficient was influenced by geological and vegetation factors, whereas land use and topographical factors influenced the drought runoff coefficient in low-frequency drought. These differences were caused by differences in the runoff component, which dominates stream discharge according to drought magnitude. Therefore, for effective water resource management, estimation of the drought runoff volume needs to consider precipitation pattern, geology, land use, and topography.