Environmental Engineering Reference
In-Depth Information
includes diverted water that is depleted, but not by the process it was intended for,
such as evaporation from the water surface in canals, deep percolation losses to
saline groundwater, and outflow of irrigation water to sea.
W ater P rodUCtivity P erformanCe i ndiCators
A set of performance indicators, based on the above-mentioned water components,
have been developed that can be used to analyze and evaluate the water productivity
at different scales/levels. These performance indicators have overcome two short-
ages or limitations of the classical efficiency indices: (i) nonagricultural water uses
are taken into consideration, and (ii) make interaction with other water users evident
and explicit. However, the lack of reliable data, particularly at basin level, confronts
the wide application of this framework and its related indicators.
The beasting obstacles are those related to subsurface water flows, recovery cost
for outflows, uncertainty about the fate of outflows, and the change in their quality.
Outflows (surface runoff and deep percolation) from fields or farms are charged as
inflows to the project level, and those from projects to the basin level. If the total
production of a farm is maintained the same but with less amount of water abstracted
from the main water supply canal of the project, this means that water productivity
of the farm has increased. If the saved water that remained in the canal was not used
by another user within the system, but rather flowed to sink (depleted), the WP of the
project has not improved. Therefore, micro water saving may not result in better WP
at a macro level. By the same token, higher WP does not necessarily result in greater
economic efficiency.
The following four performance indicators are proposed by Molden et al.
(2003):
PW of irrigation water: PWirrigation = Production/irrigation water amount
(kg m -3 )
PW of inflow water: PWinflow = Production/net inflow water amount
(kg m -3 )
PW of depleted water: PWdepleted = Production/depleted water amount
(kg m -3 )
PW of processed water: PWprocessed = Production/processed amount of
water (kg m -3 )
It should be pointed out that PW irrigation is not applicable for basin level, because
production for the whole basin includes nonirrigated areas and such as forests and
natural grazing.
e ConomiC W ater P rodUCtivity
Water Resource Use Efficiency (RUE) considers all the components of produc-
tion inputs: land, water, climate, nitrogen, cropping system, and others. When
one resource is limiting yield, other nonlimiting resources are usually used less
efficiently. If the limitation to yield is alleviated, all resources will be used more
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