Water
management is a very well discussed topic in the field of agriculture. And
evapotranspiration (ET) represents the key variable in agricultural management
and water resources. (Fisher, et al., 2017). Pereira, L.S., et al.
introduced in 2014 the paper “Crop evapotranspiration estimation with FAO56:
Past and future”, which reflects on the publication “FAO irrigation and
drainage Paper No. 56 – crop evapotranspiration” of the food and agriculture
organization (FAO) of the united nations, which was introduced in 1998. I am
going to explain what Pereira, et al. (2014) had published.
Reference
evapotranspiration
In the
first place, it is important to know that the FAO56 paper (FAO56) by Allen et
al. (1998) provides pursuing guidelines on the FAO paper No 24 (FAO24) by Doorenbos
and Pruitt (1977), which had then introduced the two-step crop coefficient-reference
ET (Kc-ETref) procedure, to estimate crop ET. ETref is defined by Doorenbos and Pruitt (1977) as “the rate of
evapotranspiration from an extensive surface of 8 to 15 cm tall, green grass
cover of uniform height, actively growing, completely shading the ground and
not short of water”. The FAO56 used this definition as the basic for their own
one. And Kc is a standardized crop coefficient to consider crop
specific influences on the ET. (Pereira, et al., 2014)
FAO56 standardized
the method of estimating the ETref to the Penman–Monteith (PM)
method and parameterized it, so that the standardized grass crop reference (ET0)
also referred to PM-ET0 can be calculated. Regarding to Pereira (2014),
this approach is highly accepted around scientist and was cited more than
11’500 times, in research articles. However, an accurate estimation of ET0
can only be achieved with weather datasets of good quality. (Pereira, et al., 2014)
Crop
evapotranspiration
Since the crop
coefficients-reference ET concept was widely used around the globe, there was
no need to change a lot. Adjustment of the FAO24 Kc coefficients on the new
PM-ET0 was required and new coefficients for more crop species and
diverse conditions were added.
Furthermore, FAO56 had worked out a dual crop coefficient concept, i.e., Kc = Kcb + Ke, because “the single Kc only represents typical conditions that can vary with wetting frequency […] and with the type of irrigation practised” (Pereira et al.,2014). Kcb, represents as the basal crop coefficient mainly plant transpiration. The other newly introduced coefficient Ke, is primarily for soil evaporation. An improvement with the dual approach, is that, the estimation of the evaporation is more accurate. (Pereira et al., 2014)
Furthermore, FAO56 had worked out a dual crop coefficient concept, i.e., Kc = Kcb + Ke, because “the single Kc only represents typical conditions that can vary with wetting frequency […] and with the type of irrigation practised” (Pereira et al.,2014). Kcb, represents as the basal crop coefficient mainly plant transpiration. The other newly introduced coefficient Ke, is primarily for soil evaporation. An improvement with the dual approach, is that, the estimation of the evaporation is more accurate. (Pereira et al., 2014)
Water
balance model tree nursery
Last but
not least, some of the guidelines of the FAO56 also influenced the business of
modelling. The dual crop approach per example, is used in several models. Pereira
predicts not only an increase in the usage of Kc-ETref in
gridded weather data, but also an increasing trend of the dual approach over
the single crop approach.
Several parameters, such as weather data for precise estimation of ET0, or all coefficients for the different species in the area, are relevant for modelling the water balance at the tree nursery in Schinzach.
Several parameters, such as weather data for precise estimation of ET0, or all coefficients for the different species in the area, are relevant for modelling the water balance at the tree nursery in Schinzach.
In
conclusion, for the “Remote sensing, GIS, and water balance”-Project in
Schinznach, it is certainly necessary to estimate the evapotranspiration for
modelling the water balance at the tree nursery. Therefore, the Kc-ETref
approach from FAO56 seems to be a solid method to estimate the potential ET, as
it is now and also will be used worldwide in the future.
References
Doorenbos J., und W.O. Pruitt. 1977. „FAO Irrigation and Drainage Paper No.
24.“
Fisher, Joshua B. u. a. 2017. „The Future of Evapotranspiration:
Global Requirements for Ecosystem Functioning, Carbon and Climate Feedbacks,
Agricultural Management, and Water Resources: THE FUTURE OF EVAPOTRANSPIRATION“.
Water Resources Research 53(4): 2618–26.
Pereira, Luis S., Richard G. Allen, Martin Smith, und Dirk Raes. 2015.
„Crop evapotranspiration estimation with FAO56: Past and future“. Agricultural
Water Management 147: 4–20.
Richard G. ALLEN, Luis S. PEREIRA, Dirk
RAES, und Martin SMITH. 1998. „FAO Irrigation and Drainage Paper“. : 333.
Hi Yannik
AntwortenLöschenYou cite many papers that are relevant for our topic, but the citation does not correspond to the standard: surnames and without initials and year in the text and correct information about the paper in the bibliography. You have made an in-between thing and omitted the bibliography. In Addition, try to avoid direct quotes in quotation marks and don't put the citation after the last point of a section. You make a good link between what you have read and our project. Apart from these formal deficiencies you make a good reference of the read to our project.
Cheers
Luzi