Onishi et al. (2025) How the hydrothermal regime differs between artificially planted coniferous and secondary deciduous forests

Identification

• Journal: Journal of Hydrology
• Year: 2025
• Date: 2025-11-22
• Authors: Takeo Onishi, Mirei Yanagihara, Masateru Senge, Ken Hiramatsu, Keigo Noda
• DOI: 10.1016/j.jhydrol.2025.134651

Research Groups

• Faculty of Applied Biological Sciences, Gifu University, Japan
• Kiso River System Land Improvement Survey and Management Office, Tokai Regional Agricultural Administration Office, Japan
• The Union Company, Ltd, Japan
• Department of Biological and Environmental Engineering, The University of Tokyo, Japan

Short Summary

This study compared the hydrothermal regimes of paired coniferous and deciduous forest catchments using observational data and a two-heat source mixing model, revealing that deciduous catchments exhibit a larger groundwater contribution and a smaller seasonal stream temperature amplitude compared to coniferous catchments.

Objective

• To clarify how vegetation differences (artificially planted coniferous versus secondary deciduous forests) impact the hydrothermal regime and stream water temperatures in steep mountainous headwater areas.

Study Configuration

• Spatial Scale: Paired catchments in a steep mountainous area of central Japan (Gifu University experimental forest). Deciduous catchment: 0.72 km², elevation 909 to 1,278 m above sea level. Coniferous catchment: 0.60 km², elevation 926 to 1,278 m above sea level. Average soil depth: 30–60 cm.
• Temporal Scale: Observational data collected from 2010 to 2018. Recording intervals were 3-10 minutes for discharge and stream temperature, and 1 hour for soil temperature.

Methodology and Data

• Models used:
  • Two-heat source end-member mixing model (developed in this study).
  • Cross-correlation analysis.
  • Flow duration curves.
  • Hysteresis-loop analysis (discharge vs. stream temperature).
  • Conventional graphical hydrograph separation method (for comparison).
• Data sources:
  • On-site observational data from paired catchments:
    • Stream discharge (m³/s) measured using right-angled triangular weirs and a semi-empirical formula (Japanese Industrial Standard B8302).
    • Stream water temperature (°C) using HOBO U20-001–04 data loggers.
    • Soil temperature (°C) at 5, 15, 30, and 50 cm depths using HOBO TMCx-HD probes and HOBO U12-008 data loggers.
    • Air pressure (for water level conversion) using HOBO U20-001–04 data loggers.
    • Precipitation (mm) measured at the downstream end of the deciduous catchment.
  • External data:
    • Air temperature data from an Automated Meteorological Data Acquisition System (AMeDAS) station.
    • Geographic data (aspect) calculated using ArcGIS 9.3.

Main Results

• The amplitude of seasonal stream water temperature change was significantly larger in coniferous catchments (17.8 °C) than in deciduous catchments (15.0 °C), a difference of 2.8 °C.
• Annual air temperature trends regulated both stream water temperature trends with a time lag of 9–11 days.
• Flow duration curves indicated that the deciduous catchment had a less variable flow regime and a larger groundwater contribution (average 50% percentile: deciduous 3.15 mm, coniferous 2.14 mm).
• Hysteresis-loops between discharge and stream temperature showed that clockwise loops (indicating a temperature drop during the recession period) were more common and pronounced in deciduous catchments, suggesting a larger groundwater contribution to rainfall-runoff.
• The developed two-heat source end-member mixing model estimated the groundwater contribution ratio to total discharge as approximately 47.4 % in the deciduous catchment and 42.4 % in the coniferous catchment.
• These model-derived groundwater contribution ratios were consistent with results obtained using the conventional graphical hydrograph separation method.
• During winter and spring, stream water temperature in the deciduous catchment was higher than in the coniferous catchment, a reversal of the summer and autumn trend, potentially due to higher soil temperatures in deciduous forests during autumn/winter.

Contributions

• Quantified the differences in hydrothermal regimes between artificially planted coniferous and secondary deciduous forests using a long-term paired catchment study.
• Developed and validated a novel two-heat source end-member mixing model that utilizes stream temperature as a signal to diagnose hydrological properties and separate groundwater and near-surface runoff components.
• Provided strong evidence that vegetation type significantly influences stream thermal regimes primarily through its impact on hydrological flow paths, particularly the contribution of groundwater.
• Highlighted the importance of soil-plant interactions, including root systems and evapotranspiration, in shaping the distinct hydrological and thermal characteristics of different forest types.

Funding

• Gifu University, Japan

Citation

@article{Onishi2025How,
  author = {Onishi, Takeo and Yanagihara, Mirei and Senge, Masateru and Hiramatsu, Ken and Noda, Keigo},
  title = {How the hydrothermal regime differs between artificially planted coniferous and secondary deciduous forests},
  journal = {Journal of Hydrology},
  year = {2025},
  doi = {10.1016/j.jhydrol.2025.134651},
  url = {https://doi.org/10.1016/j.jhydrol.2025.134651}
}