Bruno et al. (2025) Imprints of increases in evapotranspiration on decreases in streamflow during dry periods, a large-sample analysis in Germany

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Identification

• Journal: Repository for Publications and Research Data (ETH Zurich)
• Year: 2025
• Date: 2025-09-17
• Authors: Giulia Bruno, Laurent Strohmenger, Doris Duethmann
• DOI: 10.3929/ethz-c-000791935

Research Groups

Not specified in the provided text.

Short Summary

This study quantifies the contribution of increased actual evapotranspiration (E) to decreased streamflow (Q) during dry periods in 363 small German catchments. It finds that increases in E are a significant driver of decreasing summer low flows, particularly in more arid eastern regions, and are linked to shifts in the precipitation-streamflow relationship during multi-year droughts.

Objective

• To quantify the contribution of increases in catchment actual evapotranspiration (E) to decreases in streamflow (Q) during dry periods.
• To attribute trends in the magnitude of summer low flows (minimum 7-day Q during summer months) to long-term variations in E, summer precipitation (P), and spring/winter P (as proxies for storage).
• To assess potential changes in the annual P-Q relationship during a multi-year drought and investigate their relation to trends and anomalies in E and P.

Study Configuration

• Spatial Scale: 363 small catchments in Germany, each with an area less than 1000 square kilometres, without substantial water management influences.
• Temporal Scale: 1970–2019 (50 years). Specific analysis of a multi-year drought period between 1989 and 1993.

Methodology and Data

• Models used: Not explicitly mentioned; the study employed a data-based analysis using statistical methods, including multiple linear regression and correlation analysis.
• Data sources: Observational data for streamflow (Q), actual evapotranspiration (E), and precipitation (P) collected for the 363 catchments.

Main Results

• Summer low flows generally showed a decreasing tendency, with a median trend of -3.7 % per decade and an interquartile range of -7.5 to -0.6 % per decade across all catchments.
• Significant negative trends in summer low flows were observed in 31 % of the catchments, while only 2 % showed significant positive trends.
• Increases in E were identified as a relevant driver of these decreases, especially in relatively more arid eastern catchments, contributing 35 % to the long-term dynamics of summer low flows (based on multiple linear regression) and showing a correlation coefficient of -0.74 between trends in summer low flows and E.
• Changes in the P-Q relationship, characterized by lower Q than expected from pre-drought relationships, occurred in 26 % of catchments that experienced a multi-year drought between 1989 and 1993.
• These changes in the P-Q relationship were associated with concurrent strong increases in E, with a median trend of 6.1 % per decade in affected catchments.

Contributions

• Provides a data-based quantification of the contribution of increased actual evapotranspiration to decreased streamflow during dry periods, addressing a previously poorly quantified aspect.
• Highlights the critical role of increases in E, particularly in more arid catchments, for understanding and predicting future streamflow decreases.
• Offers valuable insights for water management and climate adaptation strategies by emphasizing the importance of E in hydrological responses to drought.

Funding

Not specified in the provided text.

Citation

@article{Bruno2025Imprints,
  author = {Bruno, Giulia and Strohmenger, Laurent and Duethmann, Doris},
  title = {Imprints of increases in evapotranspiration on decreases in streamflow during dry periods, a large-sample analysis in Germany},
  journal = {Repository for Publications and Research Data (ETH Zurich)},
  year = {2025},
  doi = {10.3929/ethz-c-000791935},
  url = {https://doi.org/10.3929/ethz-c-000791935}
}