MEASURING WATER USE IN A GREEN ECONOMY - UNEP

• do not express absolute availability, a ratio
of 1:10 or 10:100 or 100:1 000 would always
result in 0.1;
• do not consider sensitivity to additional
water use - adding 1 unit of use to a 1:10
situation would double the withdrawal-toavailability
to 0.2, but leave it essentially
unchanged if the ratio were 100:1 000;
• consist of two dimensions: use and
availability. As a result, countries in, for
example, the arid Sahel region are not
regarded as critical because if withdrawal
is zero, the withdrawal-to-availability will
also be zero.
Rijbersman (2006) has argued that the criticality
ratio and similar indicators are flawed in that:
• data on water resource availability do not
take into account how much could be made
available for human use;
• water withdrawal data do not take into
account how much is used consumptively
(or evapotranspired) and how much could be
available for recycling, through return flows;
• the indicators do not take into account a
society’s capacity to adapt to cope with
stress.
The International Water Management Institute
(IWMI) attempted to overcome all three
problems. Its analysis takes into account the
share of the renewable water resource available
for human needs (accounting for existing water
infrastructure) - the primary water supply. The
analysis of demand is based on consumptive
use (including evapotranspiration) and the
remainder of water withdrawn is accounted for
as return flows. The future adaptive capacity
of each country was assessed for the period
2000–2025, considering potential development
of infrastructure and an increase in irrigation
efficiency through improved water-management
policies. Countries that will not be able to meet
the estimated water demands in 2025, even
after accounting for future adaptive capacity,
are described as ‘physically water-scarce’.
Countries that have sufficient renewable
resources but would need to make very
significant investments in water infrastructure
to make these resources available are defined
as ‘economically water-scarce’.
This model is appealing; it makes some
allowance for infrastructure so is more realistic
than assessing physical scarcity alone, and the
resulting map is widely referenced. However,
a disadvantage is its complexity, as it is not
intuitive, and hence relatively inaccessible to
the wider public. The method also relies on
considerable expert judgement because data
are not available to assess all components of
the indicators. While the IWMI water scarcity
map is frequently cited, the more complex
definitions of scarcity are not used by other
authors or in other analyses. Furthermore, it
does not provide an indication of water resource
vulnerability (environmental impacts) but
focuses on water stress for humans.
4.3.3 Indices incorporating environmental
water requirements
Sullivan’s water poverty index (2003) aims to
convey both the physical availability of water
and the degree to which that water serves
humans and maintains ecological integrity. The
index clusters components in five dimensions:
access to water; water quantity, quality and
variability; water uses for domestic, food
and productive purposes; capacity for water
management; and environmental aspects.
An advantage of this indicator is its
comprehensiveness. Disadvantages are its
complexity, its difficulty to grasp intuitively
and the fact that it is not available at a
high, more detailed, spatial resolution. The
indicator represents an average of many
different elements so that counties that would
be expected to differ significantly can have
a similar water poverty index. The relative
weighting of respective variables also strongly
influences the index values.
The Smakhtin water stress index (WSI)
(Smakhtin, 2004) is applied using the
WaterGAP model and represents a modification
of Alcamo’s earlier index to incorporate
environmental flows. Alcamo considered the
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