A review on quantitative estimation of baseflow and hydrograph separation using isotopes as a tracer

A change in precipitation patterns due to recent climate change affects on the discharge rate of streams and increases the risk of natural disasters such as drought and flooding. This also affects not only the stream discharge, but also water quality, causing many problems in social, economic, and environmental aspects. In order to secure available water resources and manage nonpoint contaminant sources, it is very important to manage the baseflow, which occupies most of the streamflow. However, unlike direct runoff, the baseflow is difficult to constrain directly, and despite its importance, many studies have overlooked its importance. In this review, we examine “hydrograph separation” to better understand the baseflow, which has been commonly used and discuss the traditional graphical method, models developed based on the method and chemical and isotopic hydrograph separation. In addition, end-member and hydrograph separation uncertainties, which are the most important considerations when applying the chemical and isotopic hydrograph separation to actual water systems, have been described. Through these studies, we would like to emphasize the need for further studies on factors that cause uncertainty in quantitative hydrograph separation using conservative chemical components or isotopes as tracers in actual water systems.