Honzíčková et al. (2026) The increasing flashiness in the Czech Republic: Natural variability or recent climate change?

Identification

• Journal: Journal of Hydrology Regional Studies
• Year: 2026
• Date: 2026-02-02
• Authors: Dominika Honzíčková, Monika Šulc Michalková, Marco Borga, Rudolf Brázdil, Petr Štěpánek, Pavel Zahradníček, Pavel Coufal, Zdeňka Geršlová, Martin Caletka
• DOI: 10.1016/j.ejrh.2026.103159

Research Groups

• Department of Geography, Masaryk University, Brno, Czech Republic
• Department of Land Environment Agriculture and Forestry, University of Padova, Legnaro, Italy
• Research Center on Climate Change Impacts, University of Padova, Rovigo, Italy
• Global Change Research Institute, Czech Academy of Sciences, Brno, Czech Republic
• Czech Hydrometeorological Institute, Brno, Czech Republic
• Department of Mathematics and Statistics, Masaryk University, Brno, Czech Republic
• T. G. Masaryk Water Research Institute, Brno, Czech Republic

Short Summary

This study investigates the temporal trends and physiographic controls of flash flood flashiness in 17 Czech catchments, revealing a significant increase in flashiness in recent years, particularly in small, steep mountainous catchments, and provides a comparison within a broader European context.

Objective

• To determine if the watershed response has become flashier in the Czech Republic during the recent period (2005–2023).
• To identify which physiographic parameters most significantly influence flashiness in Czech catchments.
• To compare the hazard of Czech flash floods with major events documented across Europe and the Mediterranean.

Study Configuration

• Spatial Scale: 17 selected catchments in the Czech Republic, each with a drainage area of ≤100 km². Comparison with a pan-European and Mediterranean flash flood database.
• Temporal Scale: November 2004 to December 2023, focusing on the summer half-year (April to September). Trend analysis was performed for three periods: 2005–2010, 2011–2017, and 2018–2023.

Methodology and Data

• Models used:
  • Flashiness index (F1h, Fc) calculation (maximum rising limb steepness normalized by drainage area and time window).
  • Principal Component Analysis (PCA) for physiographic parameters.
  • k-medoids clustering for catchment categorization.
  • NRCS-curve number method for estimating runoff potential.
  • Theil-Sen method for linear trend analysis.
  • Mann-Kendall test for statistical significance of trends.
  • Kruskal–Wallis test and Dunn’s post-hoc test for median comparisons.
• Data sources:
  • Hourly discharge data from water gauge stations of the Czech Hydrometeorological Institute (CHMI).
  • Station precipitation data from CHMI.
  • Gridded hourly rainfall totals (500 m × 500 m) interpolated from CHMI automatic stations using regression kriging.
  • LiDAR-based fifth-generation digital terrain model of the CR for morphometric parameters.
  • River network and road network datasets from ˇCÚZK.
  • Land use and hydrologic soil groups (TGM WRI, 2015) for Curve Number (CN) values.
  • Czech flash flood database (Br´azdil et al., 2024).
  • Pan-European flash floods database (Amponsah et al., 2018).

Main Results

• The median 1-hour flashiness (F1h) of flash flood events in Czech catchments increased by 55 % from 0.266 mm/h² in 2005–2010 to 0.411 mm/h² in 2018–2023, a statistically significant trend (p < 0.01). This increase was consistent across all three physiographic clusters.
• Triggering rainfall (1-, 2-, and 3-hour cumulative maxima) also showed statistically significant increases in median values between the analyzed periods.
• Catchments categorized into Cluster II, characterized by small size, steep slopes (mean 13.2°), high terrain roughness (Melton ratio 0.11), high maximum elevations (median 887.95 m a.s.l.), dense river networks (2.16 km/km²), and compact shapes, exhibited the highest flashiness values.
• Czech flash floods generally show lower unit peak discharge and 1-hour flashiness values compared to European and Mediterranean flash floods, but can occasionally reach extreme intensities, such as the Jiˇcínka Stream event (Qu = 3.5 m³s⁻¹km⁻²) on June 24, 2009.
• A strong positive Pearson correlation (r = 0.84, p < 0.001) was found between maximum 1-hour flashiness and unit peak discharge.

Contributions

• This study provides the first application of the flashiness index to assess flash floods in terms of magnitude and timing on a national scale in the Czech Republic.
• It quantifies a significant increasing trend in flashiness in Czech catchments over the recent period (2005–2023), linking it to observed increases in precipitation extremeness, potentially influenced by recent climate change.
• It identifies a critical combination of physiographic parameters (small size, steep slopes, dense river network, high terrain roughness, compact shape, high maximum elevations) that significantly enhance flashiness in Czech catchments.
• The research offers a novel cross-regional comparison of Czech flash floods with pan-European and Mediterranean events, providing a broader context for their hazard and severity.
• The findings contribute valuable insights for flood risk management, planning, and the development of early warning systems by emphasizing the critical influence of both climatic and physiographic factors.

Funding

• Masaryk University [grant no. MUNI/A/1921/2025]
• ACECE project [24–14581L]
• PERUN [grant no. SS02030040]
• iNEST Project [ECS_00000043]

Citation

@article{Honzíčková2026increasing,
  author = {Honzíčková, Dominika and Michalková, Monika Šulc and Borga, Marco and Brázdil, Rudolf and Štěpánek, Petr and Zahradníček, Pavel and Coufal, Pavel and Geršlová, Zdeňka and Caletka, Martin},
  title = {The increasing flashiness in the Czech Republic: Natural variability or recent climate change?},
  journal = {Journal of Hydrology Regional Studies},
  year = {2026},
  doi = {10.1016/j.ejrh.2026.103159},
  url = {https://doi.org/10.1016/j.ejrh.2026.103159}
}