Estimation of minimum inflow time series under reservoir system operation

ABSTRACT Frequent and severe droughts driven by climate change highlight the need for reliable reservoir operation strategies. While most studies evaluate firm yield at the scale of individual reservoirs, few explicitly consider reservoir system operation of multiple reservoirs, despite its potential to enhance downstream supply reliability. The main objectives are to develop a method to estimate the firm yield of the Seomjingang and Juam Reservoirs in South Korea under reservoir system operation and to define and estimate the minimum inflow time series for each reservoir as a basis for assessing water supply reliability during extreme droughts. Results show that reservoir system operation increases firm yield by about seven percent (+1.24 cubic meters per second [CMS]), from 17.92 CMS under independent operation to 19.16 CMS under reservoir system operation, and delays reservoir depletion, thereby enhancing water supply stability during droughts. The novelty of this study lies in developing a firm-yield estimation method that incorporates reservoir system operation and establishing the concept of a minimum inflow time series. The proposed methodology establishes a quantitative framework for minimum inflow time-series estimation and highlights how reservoir system operation can enhance the resilience and reliability of long-term water supply.