All of the above applies to drought as a natural
phenomenon affecting natural terrestrial and aquatic
ecosystems. Such a situation of purely natural
droughts uninfluenced by human activities is probably now rare in much of settled Australia and many other
parts of the world. There is considerable evidence that
human activities across catchments and in water
bodies have served to exacerbate the extent and
impacts of drought. Major changes to land cover by
human activities have changed runoff and groundwater dynamics (e.g. Van Dijk et al., 2006). With land
clearance and grazing, catchment storage of water has
diminished due to a reduction in percolation of surface
water below ground, and an increase in flashy runoff
events. Urbanisation, with increases in impervious
surfaces, may also reduce catchment water storage
and produce more flashy hydrographs and more
frequent runoff events (Walsh et al., 2005). The
building of dams and weirs typically severs longitudinal connectivity and creates large reservoirs with
high volumes of water loss due to evaporation. In the
absence of drought, water extraction may reduce flow
volumes in running waters thereby increasing their
susceptibility to the effects of drought. With drought,
the increased demand for water may lead to high
levels of water extraction, hastening the damaging
impacts of drought. This may apply to large-scale
irrigation as well as to numerous local and small
extractions to meet stock and domestic demand—the
death by a thousand sucks. All of these changes have
served to exacerbate the impacts of natural drought
and to delay ecological recovery from drought. While
the effects of low flow and water extraction in
drought-affected rivers can be offset partly by industrial and sewage wastewater discharges into the rivers,
the hydrologic benefits may be compromised by
declines in water quality (Andersen et al., 2004;
Aravinthan, 2005). Rather bizarrely in some systems,
such as the Murray River in southeastern Australia, in
times of natural low flow or even drought, large
volumes of water may be delivered to downstream
irrigators, generating ‘anti-droughts’ (Boulton, 2003;
McMahon & Finlayson, 2003). We have a poor
understanding of the ecological ramifications of ‘antidrought’ flows that tend to elevate low flows and
create more stable hydraulic conditions than would
normally occur during low flow periods
All of the above applies to drought as a naturalphenomenon affecting natural terrestrial and aquaticecosystems. Such a situation of purely naturaldroughts uninfluenced by human activities is probably now rare in much of settled Australia and many otherparts of the world. There is considerable evidence thathuman activities across catchments and in waterbodies have served to exacerbate the extent andimpacts of drought. Major changes to land cover byhuman activities have changed runoff and groundwater dynamics (e.g. Van Dijk et al., 2006). With landclearance and grazing, catchment storage of water hasdiminished due to a reduction in percolation of surfacewater below ground, and an increase in flashy runoffevents. Urbanisation, with increases in impervioussurfaces, may also reduce catchment water storageand produce more flashy hydrographs and morefrequent runoff events (Walsh et al., 2005). Thebuilding of dams and weirs typically severs longitudinal connectivity and creates large reservoirs withhigh volumes of water loss due to evaporation. In theabsence of drought, water extraction may reduce flowvolumes in running waters thereby increasing theirsusceptibility to the effects of drought. With drought,the increased demand for water may lead to highlevels of water extraction, hastening the damagingimpacts of drought. This may apply to large-scaleirrigation as well as to numerous local and smallextractions to meet stock and domestic demand—thedeath by a thousand sucks. All of these changes haveserved to exacerbate the impacts of natural droughtand to delay ecological recovery from drought. Whilethe effects of low flow and water extraction indrought-affected rivers can be offset partly by industrial and sewage wastewater discharges into the rivers,the hydrologic benefits may be compromised bydeclines in water quality (Andersen et al., 2004;Aravinthan, 2005). Rather bizarrely in some systems,such as the Murray River in southeastern Australia, intimes of natural low flow or even drought, largevolumes of water may be delivered to downstreamirrigators, generating ‘anti-droughts’ (Boulton, 2003;McMahon & Finlayson, 2003). We have a poorunderstanding of the ecological ramifications of ‘antidrought’ flows that tend to elevate low flows andcreate more stable hydraulic conditions than wouldnormally occur during low flow periods
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