12. EARTH OBSERVATION DEMANDS FOR IMPROVED WATER
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fresh water resources into agriculture and natural ecosystems is a primary
concern for all. Misuse and misallocation damage arable land resources,
through salinization or waterlogging, and can threaten the consumptive
needs of other eco-systems and wetlands in the downstream end of a river
basin. Information on agro-ecological zones, land cover, land use and their
changes in time are managerial key issues.
Another need for information relates to the analysis of the performance
of irrigation projects. In physical terms, according to FAO, only 45% of
irrigation water being diverted to irrigated areas are actually consumed by
crops. The remaining 55% are termed as ‘losses’, although the definition of
losses is, hydrologically, not clear. Where water is lost to aquifers, it may not
only be recoverable, but also recoverable at times and locations where it is
more valuable than at the time it was ‘lost’. Water management in, for
instance, the Indo-Gangetic plains depends heavily on groundwater
availability during the dry season. Under such circumstances, and in simpler
cases, where downstream farmers pump water from drains carrying runoff
from upstream farmers, it is clearly misleading to consider all such flows as
‘losses’ without a clear definition of the term. The IWMI paradigm (Perry,
1998) promotes an approach which re-examines losses (quantities of water
released from storage that do not reach the crop) and efficiency (ratio
between water consumed by the crop and water delivered), noting that the
linkages between sources, uses and re-uses must be fully understood to
appraise ‘losses’ and ‘efficiency’. River basin models (e.g., Arnold and
Williams, 1987) can help in quantifying the space and time components of
these water flows. Remote sensing information used as input in these models
has been shown to improve the accuracy of the simulation process (e.g., Kite
et al., 1994) and there is a trend to replace model parameter estimation
procedures by indirect Earth Observation measurements.
In productivity terms, as water becomes the binding constraint to
agricultural production, attention has to shift from the productivity of land to
the productivity of water. The concept is well known to many farmers in arid
areas, who practice deficit irrigation, mulch the soil, and apply many other
techniques to conserve water for productive use, thus maximizing tons of
crop per cubic meter of water consumed. But this indicator has so far
attracted far less attention from policy makers and irrigation managers than
the conventional productivity measure—tons per hectare. This is due in part
to the technical difficulties of measuring actual evaporation at field and basin
scales. The complexity of the physical system is a key problem in shifting
our frame of reference from productivity of land to productivity of water.
While measures of water delivered to and within irrigation systems are
sometimes relatively well documented, return flow to drains, percolation to
RESOURCES MANAGEMENT
109
fresh water resources into agriculture and natural ecosystems is a primary
concern for all. Misuse and misallocation damage arable land resources,
through salinization or waterlogging, and can threaten the consumptive
needs of other eco-systems and wetlands in the downstream end of a river
basin. Information on agro-ecological zones, land cover, land use and their
changes in time are managerial key issues.
Another need for information relates to the analysis of the performance
of irrigation projects. In physical terms, according to FAO, only 45% of
irrigation water being diverted to irrigated areas are actually consumed by
crops. The remaining 55% are termed as ‘losses’, although the definition of
losses is, hydrologically, not clear. Where water is lost to aquifers, it may not
only be recoverable, but also recoverable at times and locations where it is
more valuable than at the time it was ‘lost’. Water management in, for
instance, the Indo-Gangetic plains depends heavily on groundwater
availability during the dry season. Under such circumstances, and in simpler
cases, where downstream farmers pump water from drains carrying runoff
from upstream farmers, it is clearly misleading to consider all such flows as
‘losses’ without a clear definition of the term. The IWMI paradigm (Perry,
1998) promotes an approach which re-examines losses (quantities of water
released from storage that do not reach the crop) and efficiency (ratio
between water consumed by the crop and water delivered), noting that the
linkages between sources, uses and re-uses must be fully understood to
appraise ‘losses’ and ‘efficiency’. River basin models (e.g., Arnold and
Williams, 1987) can help in quantifying the space and time components of
these water flows. Remote sensing information used as input in these models
has been shown to improve the accuracy of the simulation process (e.g., Kite
et al., 1994) and there is a trend to replace model parameter estimation
procedures by indirect Earth Observation measurements.
In productivity terms, as water becomes the binding constraint to
agricultural production, attention has to shift from the productivity of land to
the productivity of water. The concept is well known to many farmers in arid
areas, who practice deficit irrigation, mulch the soil, and apply many other
techniques to conserve water for productive use, thus maximizing tons of
crop per cubic meter of water consumed. But this indicator has so far
attracted far less attention from policy makers and irrigation managers than
the conventional productivity measure—tons per hectare. This is due in part
to the technical difficulties of measuring actual evaporation at field and basin
scales. The complexity of the physical system is a key problem in shifting
our frame of reference from productivity of land to productivity of water.
While measures of water delivered to and within irrigation systems are
sometimes relatively well documented, return flow to drains, percolation to