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| Titel |
Impact of climate change on freshwater ecosystems: a global-scale analysis of ecologically relevant river flow alterations |
| VerfasserIn |
P. Döll, J. Zhang |
| 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 ; 14, no. 5 ; Nr. 14, no. 5 (2010-05-21), S.783-799 |
| Datensatznummer |
250012301
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| Publikation (Nr.) |
 copernicus.org/hess-14-783-2010.pdf |
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| Zusammenfassung |
River flow regimes, including long-term average flows, seasonality, low
flows, high flows and other types of flow variability, play an important
role for freshwater ecosystems. Thus, climate change affects freshwater
ecosystems not only by increased temperatures but also by altered river flow
regimes. However, with one exception, transferable quantitative relations
between flow alterations and ecological responses have not yet been derived.
While discharge decreases are generally considered to be detrimental for
ecosystems, the effect of future discharge increases is unclear. As a first
step towards a global-scale analysis of climate change impacts on freshwater
ecosystems, we quantified the impact of climate change on five ecologically
relevant river flow indicators, using the global water model WaterGAP 2.1g
to simulate monthly time series of river discharge with a spatial resolution
of 0.5 degrees. Four climate change scenarios based on two global climate
models and two greenhouse gas emissions scenarios were evaluated.
We compared the impact of climate change by the 2050s to the impact of water
withdrawals and dams on natural flow regimes that had occurred by 2002.
Climate change was computed to alter seasonal flow regimes significantly
(i.e. by more than 10%) on 90% of the global land area (excluding
Greenland and Antarctica), as compared to only one quarter of the land area
that had suffered from significant seasonal flow regime alterations due to
dams and water withdrawals. Due to climate change, the timing of the maximum
mean monthly river discharge will be shifted by at least one month on one
third on the global land area, more often towards earlier months (mainly due
to earlier snowmelt). Dams and withdrawals had caused comparable shifts on
less than 5% of the land area only. Long-term average annual river
discharge is predicted to significantly increase on one half of the land
area, and to significantly decrease on one quarter. Dams and withdrawals had
led to significant decreases on one sixth of the land area, and nowhere to
increases.
Thus, by the 2050s, climate change may have impacted ecologically relevant
river flow characteristics more strongly than dams and water withdrawals
have up to now. The only exception refers to the decrease of the statistical
low flow Q90, with significant decreases both by past water withdrawals
and future climate change on one quarter of the land area. However, dam
impacts are likely underestimated by our study. Considering long-term
average river discharge, only a few regions, including Spain, Italy, Iraq,
Southern India, Western China, the Australian Murray Darling Basin and the
High Plains Aquifer in the USA, all of them with extensive irrigation, are
expected to be less affected by climate change than by past anthropogenic
flow alterations. In some of these regions, climate change will exacerbate
the discharge reductions, while in others climate change provides
opportunities for reducing past reductions. Emissions scenario B2 leads to
only slightly reduced alterations of river flow regimes as compared to
scenario A2 even though emissions are much smaller. The differences in
alterations resulting from the two applied climate models are larger than
those resulting from the two emissions scenarios. Based on general knowledge
about ecosystem responses to flow alterations and data related to flow
alterations by dams and water withdrawals, we expect that the computed
climate change induced river flow alterations will impact freshwater
ecosystems more strongly than past anthropogenic alterations. |
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