Author(s):
Nogueira, A.M. 
; Paço, T.A. ; Silvestre, J.C. ; Mota, M. ; Gonzalez, L.F. ; Santos, F.L. ; Pereira, L.S.
Date: 2012
Persistent ID: http://hdl.handle.net/10400.5/5721
Origin: Repositório da UTL
Subject(s): Olea europaea; sap flow; eddy covariance; irrigation; NDVI
Description
The water footprint of a crop is the volume of water that is necessary to
produce, therefore relating crop water requirements and yield. The components of
water footprint, blue, green and grey water footprints refer to the volumes of
respectively, surface and groundwater, rainfall, and water required to assimilate
pollution, which are used to produce the crop yield. Determining blue and green water
footprints is generally achieved using estimates of evapotranspiration. In the present
study we have used evapotranspiration measurements to estimate the water footprint
of a super-intensive olive grove in southern Portugal. Crop water requirements were
measured using a sap flow technique, to determine transpiration and the eddy
covariance method for direct measurement of evapotranspiration. This technique was
used for a short period, while the sap flow measurements were performed for long
periods, hence allowing the extension of the data series. Evapotranspiration measured
directly was in average close to 3 mm d-1 and the ratio of actual evapotranspiration to
reference evapotranspiration approached 0.6 for the same period.
The water footprint of the olive crop under study was lower than those
reported in literature. A possible reason relates to the density of plantation, yield and
irrigation management. The irrigated grove under study produced a high yield, which
compensates for high water use, leading to a water footprint lower than for rainfed or
less dense groves. Furthermore, as evapotranspiration measurements were used to
calculate water footprint instead of the common procedure, this might have also
caused some differences.
As recently discussed in literature, remote sensing techniques can provide
estimates of actual evapotranspiration and water balance terms when associated with
modeling. For the present study, water footprint estimates using in situ
evapotranspiration measurements were further compared with water footprint
estimates obtained with remote sensing.
