Impact assessment of climate change on environmental flow component and water temperature—Kikuchi River

Abstract The Japanese archipelago extends over a large distance from north to south exposed to the effects of climate change. The aim of this study was to assess the impacts of climate change on environmental components by using hydrological indicators. The future climate change in the region was initially projected using HadGEM2-ES and MICRO5 models in three 20-year periods (2021–2040, 2041–2060 and 2061–2080), considering two representative concentration pathways (RCP4.5 & RCP8.5). The Kikuchi streamflow was then simulated using Soil and Water Assessment Tool modelling for the baseline (1986–2016) and future periods. Finally, the magnitude, duration, timing, and frequency of extreme flows were analysed using Indicators of Hydrologic Alteration software. The results showed a decrease in discharge under both models; however, a 2 m3/s increase was predicted under HadGEM2-ES (RCP4.5) in 2041–2060. Changes in river flow affect habitat suitability in aquatic ecosystems, and might have further impacts if the effects of water temperature are also considered. In our case study, water temperature was predicted to increase by up to 4 °C by 2080. This phenomenon will change habitat suitability, because important environmental flow components, such as the peaks of high flows and large flood frequency, will also increase.