[A-HW25] Near Surface Investigation and Modeling for Groundwater Resources Assessment and Conservation

[AHW25-05] Temperature dynamics of shallow groundwater and springs in an urban area

*Jiaqi Liu¹, Kelsey Romero¹, Tomochika Tokunaga¹ (1.The University of Tokyo )

Keywords:urban, groundwater, spring, temperature

In urban areas, groundwater and spring water temperatures serve as key indicators of aquifer recharge dynamics, water quality, ecosystem health, geothermal potential, and subsurface engineering applications. This study examines the temperature dynamics of shallow groundwater and springs in a densely urbanized region of Tokyo, Japan, to identify the key factors influencing thermal variations and their implications for urban hydrology. Groundwater temperature monitoring in 2023 revealed stable temperatures throughout the year in areas with a thick unsaturated zone, whereas pronounced seasonal fluctuations of groundwater temperature were observed in areas with a thinner unsaturated zone or proximity to a losing river (Nogawa River). Spring monitoring from 2022 to 2025 showed varying thermal behaviors: some springs maintained stable temperatures year-round, while others exhibited seasonal variations correlated with air temperature. These differences appear to be influenced more by the position of spring along the hill slope and its discharge rate, rather than by local land cover conditions. Fast Fourier Transform (FFT) analysis detected diurnal and semi-diurnal cycles in both air and spring temperatures, suggesting strong thermal coupling across the air-land interface. These findings suggest that the unsaturated zone, river-groundwater interactions, hillslope geomorphology, spring discharge rates, and air-land coupling potentially play significant roles in regulating shallow groundwater and spring temperatures. To further elucidate these mechanisms, additional investigations are needed, including river water temperature monitoring, soil temperature assessments, and numerical hydrological modeling.