[A-HW27] Biodiversity, nutrients and other materials in ecosystems from headwaters to coasts

[AHW27-P05] Assessing Groundwater Recharge in a Mountainous Catchment Using Isotopes and Modelling Approach: Insights for Water Security and Disaster Resilience

*Sharon Bih Kimbi¹, Shin-ichi Onodera¹, Mitsuyo Saito¹, Yusuke Tomozawa¹, Sai Tun Aung Si¹, Kunyang Wang¹ (1.Graduate School of Advanced Science and Engineering, Hiroshima University)

Keywords:Demographic change, Recharge zones, Saké brewing , Urbanization, Saijo River catchment

Higashi-Hiroshima City depends on the Koyo Water Intake Facility, which draws water from the Otagawa and Gonokawa Rivers via a complex infrastructure of dams, tunnels, and pipelines. While this system ensures a stable water supply for domestic use, the Saké brewing industry in Saijo heavily relies on groundwater. Additionally, population growth in urban areas, contrasted with rural depopulation and aging, is influencing land use changes that can alter groundwater recharge and ecosystem service supply. However, in the event of a natural disaster or infrastructure failure that disrupts external water supply, understanding local groundwater recharge potential becomes critical for emergency planning and water security. This study integrates hydrological modeling (SWAT) with environmental isotopes (δ¹⁸O,δ²H) to assess groundwater recharge sources and pathways. The approach will help quantify water availability, identify recharge zones, and evaluate the impacts of urban expansion, climate variability, and demographic changes on water sustainability. Preliminary findings indicate that urbanization has reduced groundwater recharge while increasing surface runoff, necessitating adaptive water management strategies. The integration of demographic trends with hydrological and isotopic analyses provides a novel approach to understanding how aging populations, land use transitions, and emergency policies can influence water resource sustainability. This research will contribute to the development of resilient water policies to ensure groundwater security under both normal and extreme conditions in small urbanizing catchments.

This study is supported by the JSPS Grant-in-Aid for Challenging Research (Exploratory) (PI: Mitsuyo Saito, No. 22K19869), the Ministry of the Environment, and the Asia-Pacific Network for Global Change Research (APN).