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1. Physical Water Scarcity
This is defined in terms of the magnitude of primary water supply (PWS) development with respect to
potentially utilizable water resources (PUWR). Physical water scarce condition is reached if primary
water supply of country exceeds 60 percent of its PUWR. This means that even with highest feasible
efficiency and productivity, PUWR of a country is not sufficient to meet the demand of agriculture,
domestic, industrial sectors while satisfying its environmental needs. Countries in this category will
have to transfer water from agriculture to other sectors and import food or invest in costly desalinization
plants. Degree of Development (DoD) is defined as the primary water diversions for all sectors divided by
utilizable water resources. Primary diversions include diversions for agriculture, industry and domestic uses.
DoD = PWS/UWR
Physical water scarcity occurs when the degree of development is greater than 60 percent, in other words
more than 60 percent of the utilizable water resources are diverted. The cut-off value is set at 60 percent
to make adequate allowance for water for environmental uses (wetlands, minimum required flow in rivers).
Unfortunately, little or no information is available on water requirements for environmental uses.
To be on the safe side, 40 percent of the utilizable water resources is allocated for those uses; however
this cut-off value should be modified, as more information becomes available1. Physical scarcity indicates
a situation where water resources development has reached an upper limit, and there is insufficient water to
meet basic food and domestic needs.
[1] The value of 60 percent is chosen based on experiences in Israel. According to PODIUM estimates,
in 1995 Israel used 61 percent of the utilizable water resources. Israel can be seen as a water-short country
where substantial waterconserving efforts and investments took place. It is set as standard of maximum
achievable water development.
By Charlotte de Fraiture and Upali Amerasinghe
2. Economic Water Scarcity
This is defined in terms of the magnitude of primary water Economic water scarce countries have
sufficient water resources to meet their additional Primary Water supply (PWS) needs, but require
to increase their PWS through additional storage and conveyance facilities by more than 25 percent.
Some countries are endowed with abundant water resources but lack the financial and managerial resources
to construct infrastructure to meet water demand. To capture this type of scarcity the PODIUM model
evaluates the growth in total water diversions. A country is considered as economic water scarce if it
will be necessary to increase water supplies by development of additional storage, conveyance and
regulation systems equivalent to more than 25% of the 1995 levels
(i.e. TD2025 / TD1995 > 1.25).
Economic water scarcity implies that in spite of abundant water resources a country will not be able
to meet future water demand because its inability to cover necessary investments in water infrastructure.
Most of these countries face severe financial and development capacity problems for increasing
PWS to those levels.
By Charlotte de Fraiture and Upali Amerasinghe
3. Evaporative factor (EF)
Evaporation Factor (EFcountry) is defined by total evaporation (E) divided by primary water supply (PWS) for all sectors.
EFcountry = E/PWS
Total evaporation includes crop evaporation, non-beneficial evaporation from water bodies and bare soil
and evaporative use in the domestic and industrial sectors. Primary diversions include diversions for
agriculture, industry and domestic uses. It is advisable that the country evaporation factor does not
exceed 75 percent. An allowance of 25 percent is made to cover water needed to meet leaching requirements
and to replenish groundwater. If the country evaporation factor exceeds 75 percent environmental problems
such as salinization and groundwater table decline are anticipated. When the evaporation factor is high,
one solution is to construct more diversion and storage facilities. Development of primary water can
continue until it reaches the limit set by utilizable water resources. PODIUM uses the degree of
development to indicate the state of water resources development in a country.
By Charlotte de Fraiture and Upali Amerasinghe
4. Cereal Products Deficit / surplus
The cereal balance – i.e. cereal production minus cereal requirements – is expressed as percentage of
total cereal consumption. Countries with a positive cereal balance are considered as food exporters
while a negative balance indicates food import. A country is classified as production scarce if it has
to import more than 10 percent of its domestic food requirements. Production scarcity may occur due to
limited resources but also out of choice: countries making use of their comparative advantage in other
sectors than agriculture.
By Charlotte de Fraiture and Upali Amerasinghe
5. Environmental Water Requirement
After the total use of the Total surface Water supply by the human being, there should be left enough
water for the Environmental ecosystems in a country. We speak about the Environmental Water Requirement
(EWR). The amount of water left after the withdrawals is automatically left for the Environment, but is
this also enough for the Environmental Water Requirement. Because of this reason there is a formula.
With the formula we calculate the (E)WSI ((Environmental) Water stress Indicator), We don’t speak
direct about water scarcity or not, but we look to the affection of the withdrawals and categorize with
the formula the WSI. In The Policy Dialog Model we used this formula to calculate the EWR.
WSI = Withdrawals / (MAR-EWR)
WSI = Water Stress Indicator
Withdrawals = total of uses by the human being
MAR = Mean annual runoff / total surface water supply
EWR = Environmental Water Requirement
The Gategorization1:
WSI > 1 Overexploited (current water use is tapping into EWR) --environmentally water scarce basins
0.6 = WSI < 1 Heavily exploited (0 to 40 % of the utilizable water is still available i
n a basin before EWR are in conflict with other uses) -- environmentally stressed basins.
0.3 = WSI < 0.6 Moderately exploited (40% to 70 % of the utilizable water is still
available in a basin before EWR are in conflict with other uses)
WSI < 0.3 Slightly exploited
1) V. Smakhtin, C. Revanga and P. Döll (2004) Taking into Account Environmental Water Requirements in Global-scale Water Resources Assessments
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