Verifiable Water Use Inventory Using ICT …
21
Considering that CWA blue is applied water, WFA blue (m
3 /ha) is the blue water
footprint applied, which gives information on the blue water actually used directly
and indirectly to produce an agricultural production unit (kg or t), linking it to the
crop yield.
It should be remembered that most works on crops’ water footprint are carried out
on a regional or national scale [4, 38, 39, 45]. At these scales, it is almost impossible
to consider the specific cultivation conditions of each farm, unlike the methodology
proposed in this chapter. Thus, the calculation of the main components of the WF C
inventory, CWU green and CWU blue , is grounded on the FAO-56 methodology applied
through the free software CROPWAT (references and not on real data recorded onsite).
In short, the total amount of water used (blue and green) at field level during the
whole crop season (m
3 /ha) is the sum of CWU green and CWA blue , Eq. (19).
CWU = CWU green +CWA blue
(19)
Therefore, crop water footprint WF C is calculated with CWU, Eq. (20).
WF c =
CWU
Y
(20)
Since WF only provides information on how much water has been used to obtain
a production unit, it is necessary to know whether that amount is adequate or not. For
this purpose, the indicator Relative Irrigation Supply (RIS) [35] is used. It is defined
as the quotient between the amount of water applied (recorded in the water meter)
and the theoretical irrigation needs during the crop development period, without
accounting for the volumes of water used in different crop management practices
(indirect water uses) [21, 22, 25]. Thus, RIS values around 1.2 indicate that irrigation has been adequately performed to meet the irrigation needs of the crop taking
into account the inefficiencies associated with the irrigation system and the soil.
RIS values below and above 1.2 indicate deficit and excess irrigation, respectively.
The knowledge of monthly RIS values and for the whole irrigation season allows
identifying in which periods the main component of CWA blue (WA gn in Eq. 17) is
inadequate and to be able to modify it in the next irrigation campaigns.
RIS =
wm
i=1
lds
n’=1 (In’,i·Ai·10)
wm
i=1 A
lds
n=1 10 · (((ET c n · K s n ) − ER n ) · f CE · f Pte · f Rs )
(21)
In this case, n’ is the index for the days with irrigation events.
Schematically, Fig. 4 shows the calculation of the WF C components using the
information from the sensors by means of ITCs (dotted line boxes). The scheme
includes RIS calculation. The continuous and dotted lines show two different ways
of calculating the water footprint.
21
Considering that CWA blue is applied water, WFA blue (m
3 /ha) is the blue water
footprint applied, which gives information on the blue water actually used directly
and indirectly to produce an agricultural production unit (kg or t), linking it to the
crop yield.
It should be remembered that most works on crops’ water footprint are carried out
on a regional or national scale [4, 38, 39, 45]. At these scales, it is almost impossible
to consider the specific cultivation conditions of each farm, unlike the methodology
proposed in this chapter. Thus, the calculation of the main components of the WF C
inventory, CWU green and CWU blue , is grounded on the FAO-56 methodology applied
through the free software CROPWAT (references and not on real data recorded onsite).
In short, the total amount of water used (blue and green) at field level during the
whole crop season (m
3 /ha) is the sum of CWU green and CWA blue , Eq. (19).
CWU = CWU green +CWA blue
(19)
Therefore, crop water footprint WF C is calculated with CWU, Eq. (20).
WF c =
CWU
Y
(20)
Since WF only provides information on how much water has been used to obtain
a production unit, it is necessary to know whether that amount is adequate or not. For
this purpose, the indicator Relative Irrigation Supply (RIS) [35] is used. It is defined
as the quotient between the amount of water applied (recorded in the water meter)
and the theoretical irrigation needs during the crop development period, without
accounting for the volumes of water used in different crop management practices
(indirect water uses) [21, 22, 25]. Thus, RIS values around 1.2 indicate that irrigation has been adequately performed to meet the irrigation needs of the crop taking
into account the inefficiencies associated with the irrigation system and the soil.
RIS values below and above 1.2 indicate deficit and excess irrigation, respectively.
The knowledge of monthly RIS values and for the whole irrigation season allows
identifying in which periods the main component of CWA blue (WA gn in Eq. 17) is
inadequate and to be able to modify it in the next irrigation campaigns.
RIS =
wm
i=1
lds
n’=1 (In’,i·Ai·10)
wm
i=1 A
lds
n=1 10 · (((ET c n · K s n ) − ER n ) · f CE · f Pte · f Rs )
(21)
In this case, n’ is the index for the days with irrigation events.
Schematically, Fig. 4 shows the calculation of the WF C components using the
information from the sensors by means of ITCs (dotted line boxes). The scheme
includes RIS calculation. The continuous and dotted lines show two different ways
of calculating the water footprint.