Janicka-Kubiak (2025) Hydrological drought trends and seasonality in selected Polish catchments between 1993 and 2022 using a threshold based approach

Identification

• Journal: Scientific Reports
• Year: 2025
• Date: 2025-11-18
• Authors: Ewelina Janicka-Kubiak
• DOI: 10.1038/s41598-025-24133-1

Research Groups

• Department of Land Improvement, Environmental Development and Spatial Management, Poznań University of Life Sciences, Poland

Short Summary

This study investigates long-term trends and seasonality of hydrological droughts in selected Polish lowland catchments from 1993 to 2022, revealing a significant increase in summer and autumn low-flow events and a strong correlation between drought intensification and land use changes, particularly urbanisation.

Objective

• To examine long-term trends and seasonality of hydrological droughts in selected catchments of the Central European Lowland in Poland over hydrological years 1993–2022.
• To identify and characterise low-flow events using a threshold-based approach.
• To assess the influence of Land Use Change (LUC) on hydrological drought characteristics.
• To evaluate the persistence of drought trends using the Hurst exponent.

Study Configuration

• Spatial Scale: 15 selected lowland river catchments in Central Poland, with areas ranging from 176.01 km² to 726.28 km².
• Temporal Scale: Hydrological years 1993–2022 (30-year period).

Methodology and Data

• Models used:
  • Mann–Kendall (MK) test: Non-parametric test for detecting monotonic trends in time series.
  • Sen’s slope estimator: Quantifies the magnitude of trends.
  • Hurst exponent: Characterises long-term memory and persistence of trends in time series.
  • Peaks-over-threshold (POT) method (threshold approach): Defines drought events when river flow falls below specified thresholds (Q70, Q90, Q95).
  • Statistical analyses: Student’s t-test, correlation analysis, Principal Component Analysis (PCA), hierarchical clustering.
• Data sources:
  • Daily discharge data: 15 hydrological gauging stations from the Institute of Meteorology and Water Management (IMGW), Poland.
  • River basin and catchment boundaries, river vector layers: IIaPGW database (Second Update of River Basin Management Plans).
  • Land use data (2000, 2018): Copernicus Land Monitoring Service (CORINE Land Cover).
  • Soil type data: Harmonized World Soil Database (HWSD), version 2.0.

Main Results

• Thirteen out of fifteen analysed rivers showed a statistically significant decreasing trend in streamflow (p < 0.05), indicating intensifying water deficits. The Skora River exhibited the most pronounced negative trend.
• Significant correlations (p < 0.05) were found between the Total Number of Drought Events (TNDE) and Land Use Change (LUC), especially for events lasting ≥ 7 days at the Q90 threshold. The strongest effects were observed in the Skora, Luciąża, Widawka, and Grabia rivers, where anthropogenic land cover increased.
• A marked increase in summer and autumn low-flow events was recorded after 2002, alongside rising Seasonal Number of Drought Days (SNDD) and Seasonal Cumulative Deficit Volume (SCDV), reflecting growing water deficits. Summer was identified as the most drought-prone season.
• Drought episodes in catchments with high TNDE values tended to be short and frequent, while in catchments with fewer events, episodes were generally longer and more persistent.
• The Mean Cumulative Deficit Volume (MCDV) increased with drought duration across all rivers, with a strong positive correlation between Mean Drought Duration (MDD) and MCDV (r = 0.6521, p < 0.001).
• Hurst exponent values for all studied rivers ranged from 0.6844 to 0.8663 (average 0.78), indicating strong autocorrelation and persistence of current hydrological trends, suggesting that unfavourable conditions are likely to continue.

Contributions

• Provides a comprehensive, long-term (30-year) analysis of hydrological drought trends and seasonality in small lowland catchments in Central Poland, addressing a knowledge gap for these specific systems.
• Quantifies the significant impact of Land Use Change (LUC), particularly urbanisation, on the frequency and characteristics of short-term drought events in the region.
• Utilises a robust threshold-based approach with multiple duration and severity thresholds (Q70, Q90, Q95, and durations ≥ 7, 10, 20, 30 days) to provide a detailed characterisation of drought events.
• Employs the Hurst exponent to assess the long-term persistence of hydrological trends, offering insights into future water availability and informing strategic water resource management.
• Identifies specific catchments most vulnerable to worsening summer water conditions, providing actionable information for local and regional water management and adaptation strategies.

Funding

• Research program "Innovator plus", no. 04/2024/INN-PLUS, Poznań University of Life Sciences (Poland).

Citation

@article{JanickaKubiak2025Hydrological,
  author = {Janicka-Kubiak, Ewelina},
  title = {Hydrological drought trends and seasonality in selected Polish catchments between 1993 and 2022 using a threshold based approach},
  journal = {Scientific Reports},
  year = {2025},
  doi = {10.1038/s41598-025-24133-1},
  url = {https://doi.org/10.1038/s41598-025-24133-1}
}