Authors: Pietari Pöykkö, Mira Tammelin, Anna-Kaisa Ronkanen, Lauri Ahopelto & Pekka M. Rossi
Publication type: A1
Abstract
Seasonal groundwater level regimes are exposed to climate change, with implications for drought and flood risks, water supply, agriculture, and ecosystems. Changes in the intra-annual groundwater fluctuations are accentuated in quickly responding shallow aquifers found worldwide, but particularly in subarctic regions, where the cold winter season attenuates infiltration and evaporation. To identify the types of subarctic groundwater regimes and their responses to the changing climate, 50-year groundwater level data from 52 monitoring stations throughout Finland were analyzed. This was done by partitioning around medians (PAM) clustering of Pearson correlations and a principal component analysis (PCA) of normalized monthly values. Four distinct regimes were identified, mostly following the southwest–northeast temperature and snow condition gradients. The migration of regimes towards the colder northeastern regions could be seen between the clustering periods of 1975–1999 and 2000–2024. This migration manifested as rising winter levels and lowering summer levels, in addition to changing seasonality timing, such as the spring recharge peak advancing by an average of half a month and by up to two months. Furthermore, seasonal groundwater level responses were seen to depend on the projected surface area of the aquifer, as comparatively larger aquifers among the studied 0.1– 41 km2 scale showed a lagged regime. The results suggest that the selected approach effectively captures the spatially evolving conditions. They also highlight the importance of long-term monitoring for effective decision-making and preparedness for shortages in water availability in the changing climate.