Götte et al. (2026) The influence of lakes and reservoirs on estimated flood peaks at hourly vs. daily timescale in the Alps

Identification

• Journal: Hydrology and earth system sciences
• Year: 2026
• Date: 2026-10-09
• Authors: Jonas Götte, Paul C. Astagneau, Manuela I. Brunner
• DOI: 10.5194/hess-30-6235-2026

Research Groups

• Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland
• WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland
• Climate Change, Extremes and Natural Hazards in Alpine Regions Research Center CERC, Davos Dorf, Switzerland

Short Summary

This study investigates how lakes and reservoirs influence the ratio between daily and hourly flood peak quantiles in Alpine catchments. It finds that water bodies dampen hourly flood peaks significantly more than daily peaks, leading to greater similarity between daily and hourly flood estimates downstream of these water bodies.

Objective

• To analyze how water bodies (lakes and reservoirs) influence the ratio between instantaneous (sub-daily/hourly) and daily flood peak quantiles, and to what degree their attenuation effect is scale-dependent.

Study Configuration

• Spatial Scale: Four local case studies in Bavaria and Switzerland (Perlsee, Vilstalsee, Mertsee, Walensee); large-sample analysis of 183 catchments across Switzerland. The study focuses on the Alpine region.
• Temporal Scale: Streamflow data at 15-minute and hourly resolutions, aggregated to daily means. Annual maxima series for hydrological years (October to September) covering periods from 11 to 56 years. Flood quantiles estimated for return periods of 2 to 25 years (case studies) and 10 years (large-sample).

Methodology and Data

• Models used: Generalized Extreme Value (GEV) distributions for flood quantile estimation; Random Forest model for predicting the daily/hourly (D/H) ratio and assessing variable importance; Linear regression model (log-log transformation) to relate extreme flows to catchment area.
• Data sources: Streamflow data from the Bavarian Environment Agency (LfU) at 15-minute resolution and the Swiss Federal Office for the Environment (FOEN) at hourly resolution. Catchment shapes from CAMELS-DE and CAMELS-CH. Water body locations and characteristics from Speckhann et al. (2021) and FOEN (2021). Catchment characteristics (e.g., area, biogeographical region, soil porosity, elevation, steep area percentage, geological permeability) from CAMELS-CH.

Main Results

• Water bodies significantly dampen flood peaks, with a substantially stronger attenuation effect on hourly/sub-daily peaks than on daily peaks.
• Case studies showed sub-daily 10-year flood peaks attenuated by up to 70% downstream of reservoirs, while daily peaks decreased by up to 55% (or increased by 9% for Walensee due to larger catchment area).
• This differential dampening leads to greater similarity between daily and hourly flood peaks downstream of water bodies; for three out of four case studies, the difference between 10-year daily and sub-daily flows was less than 10% downstream.
• The ratio between daily and hourly 10-year flood peaks (D/H ratio) increases with both catchment area and the "contributing area percentage" (fraction of total catchment above the water body).
• Water bodies most notably influence the D/H ratio when more than 60% of the catchment area lies above them.
• A random forest model explained 67% of the variability in the D/H ratio, identifying contributing area percentage and catchment area as the most important predictors.
• Models trained on weakly water-body-influenced catchments (contributing area percentage < 60%) strongly underestimated the D/H ratio in strongly water-body-influenced catchments (median underestimation of -0.20), underscoring the critical role of water body influence.

Contributions

• This study is the first to systematically assess how standing water bodies influence the ratio between daily mean and instantaneous flow peaks across a large spatial domain, demonstrating the scale-dependent nature of their attenuation effect.
• It highlights that daily flood peaks can serve as a reliable proxy for hourly peaks in strongly regulated catchments, even small ones, which is crucial for flood protection infrastructure design where sub-daily data is often scarce.
• The research emphasizes the importance of incorporating spatially explicit information on water body influence (e.g., contributing area percentage) in large-sample hydrological studies, rather than excluding regulated catchments or relying on simplistic aggregated metrics.
• It advocates for consistent treatment of both lakes and reservoirs in large-sample analyses due to their similar and significant effects on flood peaks.

Funding

• Deutsche Forschungsgemeinschaft (DFG)
• Project: “Trockenheits- und Hochwasserstatistiken in regulierten Einzugsgebieten: eine multivariate Perspektive (DFStaR)”
• Grant no.: 465747089

Citation

@article{Götte2026influence,
  author = {Götte, Jonas and Astagneau, Paul C. and Brunner, Manuela I.},
  title = {The influence of lakes and reservoirs on estimated flood peaks at hourly vs. daily timescale in the Alps},
  journal = {Hydrology and earth system sciences},
  year = {2026},
  doi = {10.5194/hess-30-6235-2026},
  url = {https://doi.org/10.5194/hess-30-6235-2026}
}