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This paper introduces ArcE, a GIS tool for modelling actual evapotranspiration (E-A) from an undefined number of meteorological stations. From daily data of precipitation and temperature, ArcE uses ArcObjects as the programming language to incorporate equations and hydrological boundary conditions, in order to calculate E-A at monthly and yearly time steps. Because weather data are often missing, ArcE is programmed to use non-global models such as Hargreaves for potential evapotranspiration (E-P) and Budyko for E-A. In arid regions, where results from global and non-global models are expected to deviate, ArcE allows for the segregation of low-divergent areas suitable for interpolating E-A from those that should be excluded for mapping the variable. In the semiarid Almanzora River basin, a heterogeneous region with contrasting climate in SE Spain, divergence in lowlands with a higher aridity index was about 15% with respect to an accurate estimate of E-A from the Penman-Monteith equation. Evaluating E-A is a first step for mapping the non-evaporative fraction of precipitation as the difference in P and E-A. (C) 2011 Elsevier Ltd. All rights reserved.