4.5.4. Impacts of Climate Change on Water Resources: An Overview
This section explores the global-scale implications of climate change for water
resources stress and summarizes a few studies into climate change impacts on
several real-world water management systems. However, few published studies
consider impacts in quantitative terms on real-world systems; most published
studies infer changes in water resources from changes in streamflow.
It is very difficult to draw quantitative conclusions about the impacts of
climate change, for several reasons. Different studies have used different methodologies
and different scenarios, but, most important, different systems respond very
differently to climate change. It is possible, however, to make some qualitative
- In systems with large reservoir capacity, changes in resource reliability
may be proportionately smaller than changes in river flows.
- The potential impacts of climate change must be considered in the context
of other changes that affect water management. Few studies haveexplicitly
compared climate change with other pressures, but in many environments it
is likely that over a time horizon of less than 20 years, climate change impacts
will be very small relative to other pressures. This will depend on the system.
- The implications of climate change are likely to be greatest in systems
that currently are highly stressed.
By far the majority of studies of the impact of climate change on water resources
have concentrated on human aspects of the water environment. Only a very few
(e.g., Eheart et al., 1999; Meyer et al., 1999) have considered impacts on the
aquatic environment. Some of these studies are considered in Chapter
5, but it must be remembered that water resources systems in many parts
of the world increasingly are being managed to maintain instream and wetland
ecosystems. This either increases effective water demand or decreases water
Confidence in estimated quantitative impacts of climate change on water resources
generally is low, reflecting initial confidence in climate change scenarios
and low confidence in estimates of future pressures on water resources (as a
result of factors such as changes in demand or legislative requirements). However,
techniques for estimating the impacts of a given scenario are now well established.