Mapping reference crop evapotranspiration in Bahia, Brazil, using Hargreaves-Samani method | Mapeando a evapotranspiração de culturas de referência na Bahia, no Brasil, usando o método Hargreaves-Samani

The objective of this work was to study the spatial behavior of the reference evapotranspiration (ET o ) in the state of Bahia according to the method of 1985 Hargreaves Samani. The study includes data from 452 meteorological weather stations managed by the National Institute of Meteorology (INMET) and the National Water Agency (ANA). These stations have data of maximum, minimum and average temperatures covering the period from 1965 to 2013. Monthly maps of spatial distribution of ET o were made by geostatistical techniques with ArcGIS 9.3 software. There is also predominance of higher evaporative demands in the north of the state. The month with the highest spatial dependence of ET o was the month of October, with similar results were observed for the months of May, July, August and September. The values of spatial dependence obtained in these respective months showed an average range of 1.07 degrees. The ET o rates corresponding to the Atlantic Forest areas near the Atlantic coast in the east are uniformly distributed where predominate Humid and Super-Moist climates. Alternative models to combination equations such as Penman-Monteith provide easier and reliable way to carry out studies on ET o estimation for water resources management.  The geostatistical methods are important tools for regionalizing meteorological variables, including ET o .