Krogulec et al. (2026) Spatiotemporal assessment of groundwater drought in a river valley aquifer using standardized indices in central Poland

Identification

• Journal: Journal of Hydrology Regional Studies
• Year: 2026
• Date: 2026-01-06
• Authors: Ewa Krogulec, Katarzyna Sawicka, Sebastian Zabłocki
• DOI: 10.1016/j.ejrh.2025.103092

Research Groups

• Faculty of Geology, University of Warsaw, Warsaw, Poland

Short Summary

This study assessed spatiotemporal groundwater drought patterns in central Poland's Kampinos National Park (1999-2020) using Standardized Precipitation Index (SPI), Standardized Groundwater Index (SGI), and cluster analysis, revealing distinct drought responses between dune (prolonged, moderate intensity) and marsh (rapid, high intensity) environments.

Objective

• To assess the spatiotemporal patterns and characteristics of groundwater droughts in the Kampinos National Park area from 1999 to 2020.
• To quantify groundwater drought intensity, duration, magnitude, and response lag to meteorological deficits by integrating statistical classification with hydrogeological interpretation.
• To analyze hydrogeological drought under natural conditions, focusing on the relationship between meteorological and hydrogeological drought, while minimizing anthropogenic influences.

Study Configuration

• Spatial Scale: Kampinos National Park (KPN) and its surrounding buffer zone, central Poland, covering an area of approximately 770 square kilometers. The area is characterized by a mosaic of dune and marshland hydrogeological environments.
• Temporal Scale: 22 years, from 1 January 1999 to 1 October 2020.

Methodology and Data

• Models used:
  • Standardized Precipitation Index (SPI) for meteorological drought assessment.
  • Standardized Groundwater Index (SGI) for hydrogeological drought assessment, calculated using a non-parametric normal score transformation.
  • Hierarchical Cluster Analysis (Ward’s method with Euclidean distance) to identify homogeneous regions with common drought characteristics.
  • Pearson correlation method to determine the relationship and lag time between SPI and SGI.
  • Mann–Kendall test and Sen’s slope estimator for assessing meteorological trends.
• Data sources:
  • Groundwater table level observations from a monitoring network of 56 piezometers within the Kampinos National Park, collected biweekly and harmonized to monthly time series (1999-2020).
  • Monthly precipitation totals from 9 weather stations located in the Kampinos National Park (1999-2020).
  • Long-term annual meteorological characteristics (air temperature, snow cover duration) from the Granica station (Integrated Environmental Monitoring Station “Kampinos”).
  • Previous groundwater flow modeling results and hydrogeological zoning (Krogulec, 2004; Krogulec et al., 2019b, 2020) for contextual interpretation.
  • Dataset link: Krogulec, Ewa; Sawicka, Katarzyna; Zabłocki, Sebastian, 2025, "Dataset for spatiotemporal assessment of groundwater drought in a river valley aquifer using standardized indices in Central Poland" (https://doi.org/10.58132/DLGJBC).

Main Results

• Hierarchical cluster analysis identified 7 distinct groundwater drought response clusters (C1-C7) within the study area, reflecting varying hydrogeological conditions. An additional C0 cluster represented areas with significant anthropogenic influence outside the park boundaries.
• Drought characteristics varied significantly between hydrogeological environments:
  • Dune zones (Clusters C1, C5, C6): Exhibited prolonged drought durations (average 31-33 months, maximum 72-81 months) with relatively moderate intensity (average SGI between -1.34 and -1.42).
  • Marsh zones (Clusters C2, C3, C4, C7): Experienced shorter drought durations (average 23-28 months, maximum 50-85 months) but with higher intensity (average SGI between -1.37 and -1.54, with extreme SGI values occasionally dropping below -3).
• A notable time lag of 3 to 6 months was observed between meteorological drought (SPI) and groundwater drought (SGI). Marsh zones with shallow water tables (C2, C3, C6) showed shorter lags (3 months), while dune zones with deeper water tables and thicker vadose zones (C1, C4, C5, C7) exhibited longer lags (5-6 months).
• The correlation between SPI and SGI was strongest and most significant at a 12-month aggregation scale (R > 0.5), indicating its suitability for assessing long-term hydrogeological drought.
• The most intense drought period across all clusters occurred between 2008 and 2010, with SGI values below -2 (extreme dry), and in some marsh clusters (C2, C3, C7) even below -3.
• In areas outside the Kampinos National Park (C0 cluster), no strong correlation between SPI and SGI was observed, primarily attributed to significant anthropogenic influences such as groundwater extraction.

Contributions

• Provides a novel, comprehensive spatiotemporal analysis of hydrogeological drought in a river valley aquifer in central Poland, integrating standardized indices (SPI, SGI) with hierarchical cluster analysis.
• Quantifies and characterizes groundwater drought intensity, duration, magnitude, and response lag in diverse hydrogeological settings (dune vs. marsh), offering specific insights into their distinct hydrological behaviors.
• Demonstrates the effectiveness of using SPI as a proxy and early warning indicator for hydrogeological drought in natural, data-limited contexts, particularly at a 12-month aggregation scale.
• Highlights the critical role of local hydrogeological factors, such as vadose zone thickness, groundwater depth, and proximity to drainage channels, in modulating groundwater drought response.
• Develops a robust and adaptable methodology for hydrogeological drought monitoring that can inform targeted, localized groundwater management strategies for groundwater-dependent ecosystems under changing climatic conditions.

Funding

• This research was supported by funding acquired by Ewa Krogulec, but specific project or program details are not provided in the paper.

Citation

@article{Krogulec2026Spatiotemporal,
  author = {Krogulec, Ewa and Sawicka, Katarzyna and Zabłocki, Sebastian},
  title = {Spatiotemporal assessment of groundwater drought in a river valley aquifer using standardized indices in central Poland},
  journal = {Journal of Hydrology Regional Studies},
  year = {2026},
  doi = {10.1016/j.ejrh.2025.103092},
  url = {https://doi.org/10.1016/j.ejrh.2025.103092}
}