Publisher :
Place of publication :
Publication year : 2010
Thematic : Climate Change and Biodiversity
Language : English
Note
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 5 flow regimes. However, with one exception, transferable
quantitative relations between flow alterations and ecosystem responses have not yet
been derived. While ischarge 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
25 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 will have impacted ecologically relevant river flow characteristics much 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. 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
reduction. 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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Keywords : Crocidura grayi
Encoded by : Pauline Carmel Joy Eje
