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| Titel |
Accounting for environmental flow requirements in global water assessments |
| VerfasserIn |
A. V. Pastor, F. Ludwig, H. Biemans, H. Hoff, P. Kabat |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 18, no. 12 ; Nr. 18, no. 12 (2014-12-11), S.5041-5059 |
| Datensatznummer |
250120556
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| Publikation (Nr.) |
 copernicus.org/hess-18-5041-2014.pdf |
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| Zusammenfassung |
| As the water requirement for food production and other human needs grows, quantification of
environmental flow requirements (EFRs) is necessary to assess the amount of water needed to sustain
freshwater ecosystems. EFRs are the result of the quantification of water necessary to sustain the
riverine ecosystem, which is calculated from the mean of an environmental flow
(EF) method. In this study, five EF methods for
calculating EFRs were compared with 11 case studies of locally assessed
EFRs. We used three existing methods (Smakhtin, Tennant, and Tessmann) and
two newly developed methods (the variable monthly flow method (VMF) and the
Q90_Q50 method). All methods were compared globally
and validated at local scales while mimicking the natural flow regime. The
VMF and the Tessmann methods use algorithms to classify the flow regime into
high, intermediate, and low-flow months and they take into account
intra-annual variability by allocating EFRs with a percentage of mean
monthly flow (MMF). The Q90_Q50 method allocates
annual flow quantiles (Q90 and Q50) depending on the flow season.
The results showed that, on average, 37% of annual discharge was required
to sustain environmental flow requirement. More water is needed for
environmental flows during low-flow periods (46–71% of average
low-flows) compared to high-flow periods (17–45% of average high-flows).
Environmental flow requirements estimates from the Tennant,
Q90_Q50, and Smakhtin methods were higher than the
locally calculated EFRs for river systems with relatively stable flows and
were lower than the locally calculated EFRs for rivers with variable flows.
The VMF and Tessmann methods showed the highest correlation with the locally
calculated EFRs (R2=0.91). The main difference between the Tessmann
and VMF methods is that the Tessmann method allocates all water to EFRs in
low-flow periods while the VMF method allocates 60% of the flow in
low-flow periods. Thus, other water sectors such as irrigation can withdraw
up to 40% of the flow during the low-flow season and freshwater
ecosystems can still be kept in reasonable ecological condition. The global
applicability of the five methods was tested using the global vegetation and the Lund-Potsdam-Jena
managed land (LPJmL) hydrological model. The calculated global annual EFRs for fair
ecological conditions represent between 25 and 46% of mean annual flow
(MAF). Variable flow regimes, such as the Nile, have lower EFRs (ranging from
12 to 48% of MAF) than stable tropical regimes such as the Amazon (which
has EFRs ranging from 30 to 67% of MAF). |
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