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https://doi.org/10.5194/egusphere-2024-2678
https://doi.org/10.5194/egusphere-2024-2678
04 Sep 2024
 | 04 Sep 2024

Imprints of Increases in Evapotranspiration on Decreases in Streamflow during dry Periods, a large-sample Analysis in Germany 

Giulia Bruno, Laurent Strohmenger, and Doris Duethmann

Abstract. Decreases in streamflow (Q) during dry periods have the potential to negatively affect river ecosystems and human societies, and understanding their causes is crucial to anticipate them. The contribution of increases in catchment actual evapotranspiration (E) to decreases in Q during dry periods remains poorly quantified. To address this gap, we performed a data-based analysis for 363 small (< 1000 km2) catchments without substantial water management influences in Germany over 1970–2019. We quantified trends in the magnitude of summer low flows, i.e., the minimum 7-day Q during summer months (7dQmin, JJA). We attributed these trends to their main potential predictors (namely, long-term variations in E, summer precipitation, P, as well as spring and winter P as proxies for storage). Furthermore, we assessed potential changes in the annual P-Q relationship during a multi-year drought in the early 1990s, and investigated whether these changes were related with trends and anomalies in E and P. Summer low flows decreased significantly in 31 % of the catchments, with a median trend of -3.7 % decade-1 across all catchments. Increases in E were a relevant driver of these decreases particularly in relatively drier Eastern catchments (contribution to long-term dynamics of 7dQmin, JJA of 35 % based on multiple linear regression, and correlation coefficient between trends in 7dQmin, JJA and in E of -0.74). Changes in the P-Q relationship occurred in 26 % of the catchments that experienced a multi-year drought between 1989 and 1993, with lower Q than expected from the relationship before the drought. These changes occurred in catchments with concurrent strong increases in E (median trend of 6.1 % decade-1). Our findings point to the importance of increases in E, especially in dry catchments, when assessing potential future decreases in Q during dry periods for water management and climate adaptation strategies.

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Giulia Bruno, Laurent Strohmenger, and Doris Duethmann

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-2678', Anonymous Referee #1, 26 Sep 2024
  • RC2: 'Comment on egusphere-2024-2678', Anonymous Referee #2, 02 Oct 2024
Giulia Bruno, Laurent Strohmenger, and Doris Duethmann
Giulia Bruno, Laurent Strohmenger, and Doris Duethmann

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Short summary
Decreases in streamflow during dry periods threaten ecosystems and society, and increases in evapotranspiration may contribute to them. From data for small catchments in Germany, summer low flows decreased over 1970–2019 and increases in evapotranspiration relevantly contributed. Stronger-than-expected decreases in streamflow during the 1989–1993 drought occurred in catchments with increases in evapotranspiration. Increases in evapotranspiration need full consideration for streamflow prediction.