Konicek et al. (2026) Assessment of Water Balance and Future Runoff in the Nitra River Basin, Slovakia

Identification

• Journal: Water
• Year: 2026
• Date: 2026-01-13
• Authors: A. Konicek, Igor Leščešen, Ján Pekár, Zbyněk Bajtek, Veronika Bačová Mitková, Dana Halmová
• DOI: 10.3390/w18020208

Research Groups

• Institute of Hydrology, Slovak Academy of Sciences (SAS), Bratislava, Slovakia.
• Faculty of Mathematics, Physics, and Informatics, Comenius University Bratislava, Slovakia.

Short Summary

This study evaluates 90 years of historical water balance (1931–2020) and projects future runoff (2080–2099) for the Nitra River basin using the BILAN model. The findings reveal that rising temperatures drive significant runoff declines through increased evapotranspiration, with projected annual decreases of up to 35.2% under high-emission scenarios.

Objective

• To quantify historical trends in water balance components (precipitation, evapotranspiration, and runoff) over a 90-year period.
• To project future changes in the runoff regime for the 2080–2099 horizon under three CMIP6 Shared Socioeconomic Pathways (SSP1-1.9, SSP2-4.5, and SSP5-8.5).

Study Configuration

• Spatial Scale: Nitra River basin, Slovakia (2094 $km^2$ at the Nitrianska Streda gauge).
• Temporal Scale: Historical baseline (1930/31–2019/20) and end-century projections (2080–2099).

Methodology and Data

• Models used: BILAN (conceptual lumped-parameter monthly water balance model) and empirical linear regression analysis.
• Data sources: Historical hydrometeorological data (daily discharge, monthly precipitation, and air temperature) from the Slovak Hydrometeorological Institute (SHMÚ); future climate projections from the CMIP6 Multi-Model Ensemble (28 Global Climate Models) via the World Bank Climate Change Knowledge Portal.

Main Results

• Historical Trends: Between 1931 and 2020, mean annual runoff declined by approximately 12% (from 229 mm to 201 mm) despite a 2–3% increase in precipitation, primarily due to a +1.08 °C increase in basin-wide temperature.
• Runoff Composition: Modeled historical annual runoff (222 mm) was composed of baseflow (50.4%), interflow (41.0%), and direct runoff (8.6%).
• Empirical Sensitivity: Regression analysis determined that a 100 mm increase in annual precipitation boosts runoff by ≈41 mm, while a 1 °C temperature increase reduces it by ≈13 mm.
• Future Projections (2080–2099):
  • SSP1-1.9 (+0.88 °C): Annual runoff decreases by 8.9%.
  • SSP2-4.5 (+2.6 °C): Annual runoff decreases by 17.5%, with severe autumn reductions (up to -40.4% in December).
  • SSP5-8.5 (+5.1 °C): Annual runoff decreases by 35.2%, with summer/autumn deficits exceeding 45% (e.g., -59.2% in October).
• Seasonal Shifts: Projections indicate a shift in peak direct runoff from May–June to January–March.

Contributions

• Provides the first integrated assessment for a Slovak river basin that combines multi-decadal historical observations (90+ years) with the latest CMIP6 Shared Socioeconomic Pathways.
• Quantifies the specific sensitivity of runoff to temperature-driven evapotranspiration in Central European mid-sized basins.
• Validates complex hydrological model projections using a simple empirical regression derived from long-term historical data.

Funding

• VEGA Grant Agency (Contract No. 2/0015/23: "Comprehensive analysis of the quantity and quality of water regime development in streams and their mutual dependence in selected Slovak basins").
• Project MVTS "WATSIM II".

Citation

@article{Konicek2026Assessment,
  author = {Konicek, A. and Leščešen, Igor and Pekár, Ján and Bajtek, Zbyněk and Mitková, Veronika Bačová and Halmová, Dana},
  title = {Assessment of Water Balance and Future Runoff in the Nitra River Basin, Slovakia},
  journal = {Water},
  year = {2026},
  doi = {10.3390/w18020208},
  url = {https://doi.org/10.3390/w18020208}
}

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