Spatio-temporal variation of reference evapotranspiration from empirical methods in Chihuahua, Mexico

Introduction: Evapotranspiration is key in the management of arid agricultural areas. In Chihuahua, the volume of irrigation water is based on reference evapotranspiration (ET_o) calculated with empirical methods and extrapolated to the cropped area, which is inaccurate. The alternative is to calculate ET_o variation by spatial interpolation.
Objective: To analyze the spatio-temporal variation of ET_o using empirical methods and spatial interpolation in Chihuahua, Mexico.
Methodology: Records from 33 meteorological stations from 1960-2013 and seven ET_o estimation methods were used. The results were compared with the Penman-Monteith method, modified by FAO (PMMF), ANOVA analysis (P ≤ 0.05), and homogeneous ET_o surfaces built from the point values by spatial interpolation.
Results: The Hargreaves method (R² = 0.91, RMSE = 1.16 and ME = -0.69 mm-day^-1) had a smaller bias with respect to PMMF. ET_o values ranged from 2.5 to 7.1 mm-day^-1 in a west-east direction, with maximum values at low elevations and minimum values at high elevations, which showed the influence of the Sierra Madre Occidental on ET_o. This characteristic was most noticeable in the warm months (June to September).
Limitations of the study: The use of estimated data needs field validation.
Originality: The ET_o estimation with seven empirical methods and one spatial interpolation method to extrapolate values to areas with scarce meteorological data.
Conclusions: The Hargreaves method allows estimating the spatio-temporal variation of ET_o in large extensions and areas with limited meteorological information.