DIGITAL ATLAS OF REFERENCE EVAPOTRANSPIRATION OF TOCANTINS
DOI:
https://doi.org/10.36725/agries.v9i2.8678Keywords:
Evaluation, development, estimates, reference evapotranspiration, empirical methodsAbstract
Knowing the reference evapotranspiration (ETo) has become increasingly important in view of climate
variability, the increase in irrigated areas, the need to optimize water use, and the improvement of water
management techniques for irrigation. The Penman-Monteith method is used in various parts of the world to
determine ETo and is considered the standard method recommended by the FAO. However, for its application,
it requires that the climatic variables be the most complete to generate the reference estimate. Due to the absence of complete meteorological data in several meteorological stations, an attempt was made here to
generate a thematic map of the ETo for the state of Tocantins from alternative methods, to guarantee a
reference estimate that is closer to what is recommended. For this, the methods of Ivanov and HargreavesSamani were tested for all regions of Tocantins, with the aim of generating the digital Atlas of reference
evapotranspiration for the state of Tocantins and validating alternative estimation methods. To evaluate the
estimated ETo, by the Ivanov and Hargreaves-Samani methods in comparison to the FAO standard, daily
climatological data from 11 meteorological stations of the National Institute of Meteorology - INMET, all
distributed in the state of Tocantins, with at least ten years of existence data were used. Climatological data
from the NCEP/NCAR reanalysis were also used, in a 30 - year time series. The evaluation of the models was
based on the following statistical tools: linear regression (r), coefficient of determination (r²); standard error
of estimate (EPE); and concordance index (d). Meteorological data, saved in Excel 2019 spreadsheets, were
worked on scripts in the Python 3.8 language in the IDE Jupyter Notebook 6.0.3. After validating the methods,
they were used to generate ETo thematic maps. Based on the evaluations, the methods of Ivanov and
Hargreaves-Samani were satisfactory as alternatives to the PM-FAO for the state of Tocantins. The
Hargreaves-Samani equation presents a better fit in relation to Ivanov in the dry season. Monthly and annual
ETo thematic maps were generated. The Hargreaves-Samani method was the method that best replaced the
Penman-Monteith FAO56 method for estimating reference evapotranspiration in the state of Tocantins at any
time of the year.
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