Preprints
https://doi.org/10.5194/hess-2021-260
https://doi.org/10.5194/hess-2021-260

  11 May 2021

11 May 2021

Review status: this preprint is currently under review for the journal HESS.

Environmental flow envelopes: quantifying global, ecosystem–threatening streamflow alterations

Vili Virkki1,, Elina Alanärä1,, Miina Porkka1,2, Lauri Ahopelto1,3, Tom Gleeson4,5, Chinchu Mohan4,6, Lan Wang-Erlandsson7,8, Martina Flörke9, Dieter Gerten10,11, Simon N. Gosling12, Naota Hanasaki13, Hannes Müller Schmied14,15, and Matti Kummu1 Vili Virkki et al.
  • 1Water and Development Research Group, Aalto University, Espoo, Finland
  • 2Global Economic Dynamics and the Biosphere, Royal Swedish Academy of Sciences, Stockholm, Sweden
  • 3Finnish Environment Institute, Helsinki, Finland
  • 4Department of Civil Engineering, University of Victoria, Victoria, British Columbia, Canada
  • 5School of Earth and Ocean Sciences, University of Victoria, Victoria, British Columbia, Canada
  • 6Global Institute for Water Security, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
  • 7Stockholm Resilience Centre, Stockholm University, Stockholm, Sweden
  • 8Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden
  • 9Institute of Engineering Hydrology and Water Resources Management, Ruhr-University Bochum, 44801, Bochum, Germany
  • 10Potsdam Institute for Climate Impact Research (PIK), Member of the Leibniz Association, Potsdam, Germany
  • 11Humboldt-Universität zu Berlin, Geography Department, Berlin, Germany
  • 12School of Geography, University of Nottingham, Nottingham, NG7 2RD, United Kingdom
  • 13National Institute for Environmental Studies, Tsukuba, Japan
  • 14Institute of Physical Geography, Goethe University Frankfurt, Frankfurt am Main, Germany
  • 15Senckenberg Leibniz Biodiversity and Climate Research Centre (SBiK-F), Frankfurt am Main, Germany
  • These authors contributed equally to this work.

Abstract. Human actions and climate change have drastically altered river flows across the world, resulting in adverse effects on riverine ecosystems. Environmental flows (EFs) have emerged as a prominent tool for safeguarding riverine ecosystems. However, at the global scale, the assessment of EFs is associated with significant uncertainty. Here, we present a novel method to determine EFs by Environmental Flow Envelopes (EFE), which is an envelope of variability bounded by discharge limits within which riverine ecosystems are not seriously compromised. The EFE is defined globally in approximately 4,400 sub–basins at monthly time resolution, considering also the methodological uncertainties related with global EF studies. In addition to a lower bound of discharge, the EFE introduces an upper bound of discharge, identifying areas where streamflow has increased substantially. Further, instead of only showing whether EFs are violated, as commonly done, we quantify, for the first time, the frequency, severity, and trends of EFE violations, which can be considered as potential threats to riverine ecosystems.

We use pre–industrial (1801–1860) quasi-natural discharge and a suite of hydrological EFR methods and global hydrological models to estimate EFE, applying data from the ISIMIP 2b ensemble. We then compare the EFEs to recent past (1976–2005) discharge to assess the violations of the EFE. We found that the EFE violations most commonly manifest themselves by insufficient streamflow during the low flow season, with less violations during intermediate flow season, and only few violations during high flow season. These violations are widespread: discharge in half of the sub–basins of the world has violated the EFE during more than 5 % of the months between 1976 and 2005. The trends in EFE violations have mainly been increasing during the past decades and will likely remain problematic with projected increases in anthropogenic water use and hydroclimatic changes. Indications of excessive streamflow through EFE upper bound violations are relatively scarce and spatially distributed, although signs of increasing trends can be identified and potentially attributed to climate change. While the EFE provides a quick and globally robust way of determining environmental flow allocations at the sub–basin scale, local fine–tuning is necessary for practical applications and further research on the coupling between quantitative discharge and riverine ecosystem responses is required.

Vili Virkki et al.

Status: open (until 06 Jul 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on hess-2021-260', Anonymous Referee #1, 20 May 2021 reply
  • RC2: 'Comment on hess-2021-260', Anonymous Referee #2, 23 Jun 2021 reply

Vili Virkki et al.

Vili Virkki et al.

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Short summary
Direct and indirect of human actions have altered streamflow across the world since the pre-industrial time. Here, we introduce a novel method of Environmental Flow Envelopes (EFEs); this is an envelope of safe discharge variability within which riverine ecosystems are not seriously compromised. By assessing the violations of the EFE, we comprehensively quantify the frequency, severity, and trends of flow alteration during the past decades, illustrating anthropogenic effects on streamflow.