MEASURING WATER USE IN A GREEN ECONOMY - UNEP

Measuring water use in a green economy
the resource not linked to population.
Other indicators of human water requirements
include Gleick (1996) who proposed 50 litres
of water per day as the ‘basic human water
requirement’ (for drinking, sanitation, bathing
and food preparation) and estimated the
percentage of individuals in each country who
fell short of this threshold.
Ohlsson (2000) built on the Falkenmark
indicator by integrating a society’s ‘adaptive
capacity’: its ability to alter overall freshwater
availability using economic, technological or
other means. The United Nations Development
Programme’s Human Development Index
is used to weight the Falkenmark index and
Ohlsson (2000) called this a ‘Social Water Stress
Index’.
4.3.2 Water resource vulnerability indices
Shiklomanov (1991) led the first attempts to
consider the ratio of demand to availability.
He compared national water demand in the
industrial, agricultural and domestic sectors to
national annual water availability.
Raskin et al. (1997) built on this work, replacing
water demand with water withdrawal, and
defining the ‘Water Resources Vulnerability
Index’ as total annual withdrawals as a
percentage of available water resources. Water
withdrawals are defined as the amount of
water taken out of rivers, streams or aquifers
to satisfy human needs for water. The authors
suggest that a country is scarce if annual
withdrawals are between 20 per cent and 40
per cent of annual supply, and severely waterscarce
if the figure exceeds 40 per cent.
Alcamo et al. (2000) also use this definition
for their ‘criticality ratios’: the ratio of water
withdrawals for human use to total renewable
water resources. Alcamo et al. apply the ratios
using their global model WaterGap.
Vorosmarty et al. (2005) used a similar
approach, introducing indices for local
relative water use and water reuse and
applying them using geospatial tools at 8 km
resolution. Water use was represented by
local demand: the sum of domestic, industrial
and agricultural water withdrawals. Dividing
local demand by the river corridor discharge
entering from upstream cells yields an index
of local relative water use. A high degree of
stress is indicated when this ratio exceeds 0.4.
Total water use from all cells divided by the
river corridor discharge gives the water reuse
index, which represents the extent to which
runoff is recycled or reused as it accumulates
and flows toward the basin mouth.
Pfister et al. (2009) proposed a water scarcity
index, which is often used as a characterisation
factor for water consumption in life-cycle
impact assessment (LCIA). Using the
withdrawal-to-availability ratio calculated for
each river basin, a weighting factor is applied
for each river basin to account for variation
in monthly or annual flows. Finally, a logistic
transformation of the transformed withdrawalto-availability
values gives a water scarcity
index.
The water exploitation index (WEI), based
on data collected via a joint OECD–Eurostat
questionnaire, also uses the ratio of annual
total water abstraction to available long-term
freshwater resources. A WEI above 20 per cent
implies that a water resource is under stress,
and more than 40 per cent indicates severe
stress and clearly unsustainable use of the
resource (Raskin et al., 1997).
Most withdrawal-to-availability indicators are
based on average volumes per year, which
do not reveal sensitive seasonal effects and
periods when availability and demand differ.
For example, many of the systems cited above
would not indicate as stressed or sensitive
those areas with high winter rainfall but low
water ‘storage capacity’ (e.g. calcareous soils
in the Mediterranean). Pfister et al. (2009)
include monthly variability, and for European
applications the European Environment Agency
is currently developing an application of the
WEI that disaggregates the information at the
monthly and river-basin levels (EEA, 2012).
Concern can be expressed that withdrawal-toavailability
indicators:
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