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This last factor means that where resources are
in excess, they are used less and river runoff is virtually unchanged. In the regions
where water deficits are due to anthropogenic factors, the effects become more and more
tangible with every year. In the future, as water requirements and technological and
economic possibilities expand, the volume and scale of runoff transfer would seem likely
to increase. As this occurs, the principal difficulties in developing large-scale measures
for runoff diversion will be determined more by the necessity for detailed estimation of
effects on the natural environment, reliable forecasts of possible ecological consequences
(plus the development and realisation of effective measures for their elimination) rather
than simply by financial and technological possibilities. In the long term, with
anthropogenic global climate change and redistribution of heat and moisture over the
EarthÕs surface taking place, as some scientists believe, it could be necessary to return
to large-scale projects for major river diversions such as the projects favoured in the
1960-70s. However, we now know more about potential complications. First, unfavourable
climatic changes could embrace vast areas, including the basins where runoff withdrawals
are planned and, second, the uncertainties surrounding the scale of possible regional
climatic changes are probably too great to be able to realistically plan such large-scale
measures, even for the far distant future.
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