18
C. M. Flores-Cayuela et al.
the next 7 days to determine if irrigation is necessary. To do this, the last calculated
Dr n is used as a starting point; it is considered that the irrigation depth I n will be the
recommended one (I n = IR n ) and the effective precipitation ER n is obtained from
Eq. (9), using precipitation predictions for the value of P n .
The accuracy of irrigation programming resulting from the application of this
methodology affects the values of the green and blue water uses of the crops (water
footprint inventory). In the programming process, the procedures to quantify the
green and blue water use of the crops are clearly identified. This methodology also
minimizes possible losses in crop yields due to water stress by applying the right
amount of water at the right time. In this way, the water footprint of the crops is
optimized for their production conditions.
2.3 Water Footprint Inventory
The international standard ISO 14046 defines the Water Footprint as a “metric”. The
definition has been left open to allow the choice of the quantification method. In
addition, as already mentioned in the introduction, this standard is based on the LCA
life cycle analysis and focuses on analyzing environmental impacts related to water.
This together with the recognized potential of the concept introduced by Hoekstra
[29] made the scientific community develop a large number of methodologies for
water footprint assessment [4, 5, 7, 27, 30, 45]. There are so many evaluation methods
that some studies [38] have focused on to analyze as to which is the best methodology
to determine the main impact categories.
Although the methodology proposed by Water Footprint Network (WFN) is not
well adapted by LCA due to the absence of characterization factors to weigh the
volumes of water consumed against the impact, its approach in the field of water
resources management makes it suitable for quantifying water use. Hoekstra et al.
[28] indicate that to serve LCA, it could be said that the first step of the WFN
methodology, “water footprint accounting”, contributes to the life cycle inventory.
Based on the virtual water concept [2], Hoekstra [29] establishes the water footprint as the sum of all water volumes used in a supply chain, comprising blue, green
and gray water. Green water is defined as rainwater that is stored in the soil and evapotranspired by the plant during the growing period (ET green ), which is equivalent
to the concept of effective precipitation (ER). This category of water is especially
significant in outdoor crops. Blue water (ET blue ) is defined as the volume of freshwater extracted from surface water sources (rivers, lakes, ponds) and/or groundwater
(aquifers) that is evapotranspired during the crop season. It represents the applied
irrigation, which according to the methodology described in the previous section can
be calculated to satisfy the crop irrigation needs fully or partially, depending on the
crop and the selected irrigation strategy. In short, it is water that is applied to the
product and does not return to the environment from which it was initially withdrawn,
in other words, it is the water that is “lost” in a particular region [6]. This concept
is also known as freshwater consumptive uses. Finally, gray water is an indicator
C. M. Flores-Cayuela et al.
the next 7 days to determine if irrigation is necessary. To do this, the last calculated
Dr n is used as a starting point; it is considered that the irrigation depth I n will be the
recommended one (I n = IR n ) and the effective precipitation ER n is obtained from
Eq. (9), using precipitation predictions for the value of P n .
The accuracy of irrigation programming resulting from the application of this
methodology affects the values of the green and blue water uses of the crops (water
footprint inventory). In the programming process, the procedures to quantify the
green and blue water use of the crops are clearly identified. This methodology also
minimizes possible losses in crop yields due to water stress by applying the right
amount of water at the right time. In this way, the water footprint of the crops is
optimized for their production conditions.
2.3 Water Footprint Inventory
The international standard ISO 14046 defines the Water Footprint as a “metric”. The
definition has been left open to allow the choice of the quantification method. In
addition, as already mentioned in the introduction, this standard is based on the LCA
life cycle analysis and focuses on analyzing environmental impacts related to water.
This together with the recognized potential of the concept introduced by Hoekstra
[29] made the scientific community develop a large number of methodologies for
water footprint assessment [4, 5, 7, 27, 30, 45]. There are so many evaluation methods
that some studies [38] have focused on to analyze as to which is the best methodology
to determine the main impact categories.
Although the methodology proposed by Water Footprint Network (WFN) is not
well adapted by LCA due to the absence of characterization factors to weigh the
volumes of water consumed against the impact, its approach in the field of water
resources management makes it suitable for quantifying water use. Hoekstra et al.
[28] indicate that to serve LCA, it could be said that the first step of the WFN
methodology, “water footprint accounting”, contributes to the life cycle inventory.
Based on the virtual water concept [2], Hoekstra [29] establishes the water footprint as the sum of all water volumes used in a supply chain, comprising blue, green
and gray water. Green water is defined as rainwater that is stored in the soil and evapotranspired by the plant during the growing period (ET green ), which is equivalent
to the concept of effective precipitation (ER). This category of water is especially
significant in outdoor crops. Blue water (ET blue ) is defined as the volume of freshwater extracted from surface water sources (rivers, lakes, ponds) and/or groundwater
(aquifers) that is evapotranspired during the crop season. It represents the applied
irrigation, which according to the methodology described in the previous section can
be calculated to satisfy the crop irrigation needs fully or partially, depending on the
crop and the selected irrigation strategy. In short, it is water that is applied to the
product and does not return to the environment from which it was initially withdrawn,
in other words, it is the water that is “lost” in a particular region [6]. This concept
is also known as freshwater consumptive uses. Finally, gray water is an indicator