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Globally widespread and increasing violations of environmental flow envelopes

Virkki, Vili; Alanärä, Elina; Porkka, Miina; Ahopelto, Lauri; Gleeson, Tom; Mohan, Chinchu; Wang-Erlandsson, Lan; Flörke, Martina; Gerten, Dieter; Gosling, Simon N; Hanasaki, Naota; Schmied, Hannes Müller; Wanders, Niko; Kummu, Matti

Authors

Vili Virkki

Elina Alanärä

Miina Porkka

Lauri Ahopelto

Tom Gleeson

Chinchu Mohan

Lan Wang-Erlandsson

Martina Flörke

Dieter Gerten

Dr SIMON GOSLING SIMON.GOSLING@NOTTINGHAM.AC.UK
Professor of Climate Risks and Environmental Modelling

Naota Hanasaki

Hannes Müller Schmied

Niko Wanders

Matti Kummu



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 the riverine ecosystems, but at the global scale, the assessment of EFs is associated with high uncertainty related to the hydrological data and EF methods employed. Here, we present a novel, in-depth global EF assessment using environmental flow envelopes (EFEs). Sub-basin specific EFEs are determined for approximately 4,400 sub-basins at a monthly time resolution, and their derivation considers the methodological uncertainties related with global-scale EF studies. In addition to a lower bound of discharge based on existing EF methods, we introduce an upper bound of discharge in the EFE. This upper bound enables identifying areas where streamflow has substantially increased above natural levels. Further, instead of only showing whether EFs are violated over a time period, we quantify, for the first time, the frequency, severity, and trends of EFE violations during the recent historical period. Discharge was derived from global hydrological model outputs from the ISIMIP 2b ensemble. We use pre-industrial (1801-1860) quasi-natural discharge together with a suite of hydrological EF methods to estimate the EFEs. We then compare the EFEs to recent historical (1976-2005) discharge to assess the violations of the EFE. These violations most commonly manifest themselves by insufficient streamflow during the low-flow season, with fewer violations during the intermediate-flow season, and only a few violations during the high-flow season. The EFE violations are widespread and occurring in half of the sub-basins of the world during more than 5% of the months between 1976 and 2005, which is double compared to the pre-industrial period. The trends in EFE violations have mainly been increasing, which will likely continue in the future with the projected hydroclimatic changes and increases in anthropogenic water use. Indications of increased upper extreme streamflow through EFE upper bound violations are relatively scarce and dispersed. Although local fine-tuning is necessary for practical applications, and further research on the coupling between quantitative discharge and riverine ecosystem responses at the global scale is required, the EFEs provide a quick and globally robust way of determining environmental flow allocations at the sub-basin scale to inform global research and policies on water resources management.

Citation

Virkki, V., Alanärä, E., Porkka, M., Ahopelto, L., Gleeson, T., Mohan, C., …Kummu, M. (in press). Globally widespread and increasing violations of environmental flow envelopes. Hydrology and Earth System Sciences,

Journal Article Type Article
Acceptance Date May 11, 2022
Deposit Date May 13, 2022
Publicly Available Date May 13, 2022
Journal Hydrology & Earth System Sciences
Print ISSN 1027-5606
Publisher European Geosciences Union
Peer Reviewed Peer Reviewed
Public URL https://nottingham-repository.worktribe.com/output/8048530

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