Pöykkö et al. (2026) Changes in the annual cycle in shallow subarctic groundwater regimes over 50 years

Identification

• Journal: Journal of Hydrology
• Year: 2026
• Date: 2026-10-01
• Authors: Pietari Pöykkö, Mira H. Tammelin, Anna‐Kaisa Ronkanen, Lauri Ahopelto, Pekka Matias Rossi
• DOI: 10.1016/j.jhydrol.2026.136554

Research Groups

• Water, Energy, and Environmental Engineering Research Unit, University of Oulu (Pietari Pöykkö)
• Finnish Environment Institute (Mira Tammelin, Anna-Kaisa Ronkanen, Lauri Ahopelto)

Short Summary

This study analyzed 50-year groundwater level data from 52 monitoring stations in Finland to identify changes in the annual cycle of shallow subarctic groundwater regimes over recent decades. The results show that the regimes have migrated northeast between the two time periods (1975–1999 and 2000–2024), with rising winter levels and lowering summer levels, as well as changing seasonality timing.

Objective

• Identify distinct annual groundwater level regimes in shallow subarctic regions
• Investigate changes in regime timing and shape over recent decades
• Examine the relationship between climate change and groundwater dynamics

Study Configuration

• Spatial Scale: Finland, a country located in Northern Europe, with a range of hydrogeological conditions and climate gradients.
• Temporal Scale: 50-year dataset from 1975 to 2024.

Methodology and Data

• Models used: Partitioning Around Medoids (PAM) clustering and Principal Component Analysis (PCA)
• Data sources: Groundwater level data from 52 monitoring stations in Finland, obtained from the Finnish Hydrological GW Background Monitoring Network

Main Results

• Four distinct groundwater regimes were identified, with a southwest–northeast gradient.
• The regimes have migrated northeast between the two time periods (1975–1999 and 2000–2024).
• Rising winter levels and lowering summer levels were observed in most stations.
• Changes in seasonality timing, such as the spring recharge peak advancing by an average of half a month.

Contributions

• This study provides new insights into the changes in groundwater dynamics over recent decades in shallow subarctic regions.
• The results highlight the importance of long-term monitoring for effective decision-making and preparedness for shortages in water availability in the changing climate.

Funding

• Not specified

Citation

@article{Pöykkö2026Changes,
  author = {Pöykkö, Pietari and Tammelin, Mira H. and Ronkanen, Anna‐Kaisa and Ahopelto, Lauri and Rossi, Pekka Matias},
  title = {Changes in the annual cycle in shallow subarctic groundwater regimes over 50 years},
  journal = {Journal of Hydrology},
  year = {2026},
  doi = {10.1016/j.jhydrol.2026.136554},
  url = {https://doi.org/10.1016/j.jhydrol.2026.136554}
}