Performance of Reference Evapotranspiration Estimation Methods at the Southern Paraná, Brazil

Knowing the atmospheric potential demand (ETo) implies in quantifying the ability of vegetated surfaces in absorbing water from the soil aiming at irrigation scheduling, crop yield prediction and water balance studies at a given site. Such information is extremely useful even under non-irrigated systems, for it makes possible to adjust sowing date within the crop growing season as a function of the local soil water availability, conditioning therefore a better reclamation of rainfall regime. Crop yield is significantly affected by the atmospheric conditions in order to galvanize researchers to scrutinize the regime of physical environment variables which directly interfere into the consumption of natural resources of crops in production fields. The aim of the current work was to investigate which of the atmospheric evaporative demand estimation methods are more suitable to depict physical reality of the water loss process in order to maximize crop yield and optimize irrigation scheduling under the climatic conditions of Southern Paraná, Brazil. The following methods were tested at two distinct sites of the studied region concerning its performance, taking into account the Penman-Monteith (FAO-56) approach as a standard reference for comparison purposes: simplified Penman, modified Bowen, Hargreaves-Samani, Camargo, and Linacre. The meteorological elements used for the calculation of ETo were monitored by an automatic weather station from Campbell Scientific Inc. throughout the years of 2008 through 2013. We concluded that empirical methods showed an unsatisfactory performance, whereas those methods that took into consideration net radiation as an input variable performed better, being the latter hence to be considered for agricultural planning and also for agrometeorological studies aiming at sustainability of the regional agriculture. The simplified Penman and modified Bowen methods were more accurate for estimating ETo in order to provide irrigation scheduling and indicate local soil water status at the region in study, because dismiss information on wind regimes that govern evapotranspiration rates.