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M. B. Johnson and M. Mehrvar
where WF green,consumptive is the consumptive green WF (L
3 /unit), Etc ,r is the evapotranspiration of the crop under rain-fed conditions (LT
−1 ), A vineyard is the area of
the vineyard (L
2 ) and ˙
U F is the production rate of functional unit chosen for the
assessment (unit/T).
5.2.2 Water-Balance Approach
Using the water-balance approach, a control volume around a vine, that includes both
its canopy and root system, is defined. The green WF is defined as the difference
between the outflow components of rainwater (ET, drainage, runoff) and the net
precipitation that reaches the soil surface (i.e. excluding precipitation intercepted
by the vine and cover crop canopy). This is presented visually in Fig. 3 with the
calculation as follows [27]:
W F green,balance =
Out f low − N et Preci pitation
˙
U F
=
Et c,r + D r + R r
− (P − P i )
A vineyard
˙
U F
(4)
Fig. 3 Control volume used for the water-balance footprint approach for the viticultural stage of
wine making (adapted from [27])