A Model for the Assessment of the Water Footprint …
79
crop and soil data, it establishes the need to resort to irrigation if the amounts of
water provided by rain do not cover the needs to ensure the survival of the crop.
The ETo is obtained from the relative humidity, the maximum and minimum air
temperature, the sunshine and the wind speed. These climatic data needed for the
calculation are measured from weather stations, equipped with humidity, radiation,
wind speed and temperature measurements. The data used in the calculation have
been extracted from the statistics developed by agencies and/or institutes, using the
meteorological data collected by the stations closest to the study area. Specifically,
data are extracted from the FAO CLIMWAT database [14].
Adapting the crop coefficient to the garden coefficient
Due to the very different conditions that exist between the field crop areas and the
urban gardens and green areas covered in this paper, it is not possible to apply
directly the crop coefficients extracted from the CROPWAT database based on data
from FAO publications. There are three main differences between the farmland and
the urban garden areas; firstly, related to the location and the environment, since in
these garden areas a microclimate effect is generated due to their relative situation
with the surrounding buildings, which influences aspects such as the predominant
winds and the generation of shade, other aspects also influence, such as road traffic
and paved areas; secondly, due to the differences in species located within the same
garden space, with different levels of species such as shrubs, trees or herbaceous
being found simultaneously without the predominance of one over the other and all
with different irrigation needs; and finally, related to the lack of uniformity in the
density of vegetation, with greater soil evaporation in areas where the density of
vegetation is lower.
On the basis of all this, the garden coefficient (Cg) method is used, which is based
on the method described above, introducing the necessary modifications to specify
the losses that occur in the garden areas (garden evapotranspiration (ETg)) (Fig. 6,
Eq. 14).
In the case of the gardens, the concept of “maximum productivity” applied to the
areas of cultivation is not applied, this concept is changed to “adequate aesthetics”,
thus achieving the optimum results with the minimum contribution of water, quantities that are much lower than those needed in the crops. For this reason, in gardening,
a correction coefficient called the garden coefficient (Cg) will be applied, which
allows the calculation of the amount of water necessary for the gardens to obtain
an adequate aesthetic, that is to say, an adequate growth and healthy appearance. To
take into account these conditions, the species factor (Fs), the density factor (Fd) and
the microclimate factor (Fm) appear (Fig. 6, Eq. 15). The garden coefficient is not a
constant, since it reflects the variations in the water needs of the plants throughout
their development, so this value will vary through the different stages of plant growth,
from germination, through growth, flowering and pruning, etc. It is considered an
average garden coefficient obtained for a period of one year Fig. 7.
79
crop and soil data, it establishes the need to resort to irrigation if the amounts of
water provided by rain do not cover the needs to ensure the survival of the crop.
The ETo is obtained from the relative humidity, the maximum and minimum air
temperature, the sunshine and the wind speed. These climatic data needed for the
calculation are measured from weather stations, equipped with humidity, radiation,
wind speed and temperature measurements. The data used in the calculation have
been extracted from the statistics developed by agencies and/or institutes, using the
meteorological data collected by the stations closest to the study area. Specifically,
data are extracted from the FAO CLIMWAT database [14].
Adapting the crop coefficient to the garden coefficient
Due to the very different conditions that exist between the field crop areas and the
urban gardens and green areas covered in this paper, it is not possible to apply
directly the crop coefficients extracted from the CROPWAT database based on data
from FAO publications. There are three main differences between the farmland and
the urban garden areas; firstly, related to the location and the environment, since in
these garden areas a microclimate effect is generated due to their relative situation
with the surrounding buildings, which influences aspects such as the predominant
winds and the generation of shade, other aspects also influence, such as road traffic
and paved areas; secondly, due to the differences in species located within the same
garden space, with different levels of species such as shrubs, trees or herbaceous
being found simultaneously without the predominance of one over the other and all
with different irrigation needs; and finally, related to the lack of uniformity in the
density of vegetation, with greater soil evaporation in areas where the density of
vegetation is lower.
On the basis of all this, the garden coefficient (Cg) method is used, which is based
on the method described above, introducing the necessary modifications to specify
the losses that occur in the garden areas (garden evapotranspiration (ETg)) (Fig. 6,
Eq. 14).
In the case of the gardens, the concept of “maximum productivity” applied to the
areas of cultivation is not applied, this concept is changed to “adequate aesthetics”,
thus achieving the optimum results with the minimum contribution of water, quantities that are much lower than those needed in the crops. For this reason, in gardening,
a correction coefficient called the garden coefficient (Cg) will be applied, which
allows the calculation of the amount of water necessary for the gardens to obtain
an adequate aesthetic, that is to say, an adequate growth and healthy appearance. To
take into account these conditions, the species factor (Fs), the density factor (Fd) and
the microclimate factor (Fm) appear (Fig. 6, Eq. 15). The garden coefficient is not a
constant, since it reflects the variations in the water needs of the plants throughout
their development, so this value will vary through the different stages of plant growth,
from germination, through growth, flowering and pruning, etc. It is considered an
average garden coefficient obtained for a period of one year Fig. 7.