ArcB is a GIS tool for modelling annual diffuse infiltration (R-P) from precipitation (P) on a plot scale that uses ArcObjects as the programming language to incorporate equations and boundary conditions for the water-balance consistency. Because detailed weather, soil, and vegetation data are often missing, ArcB uses well-known non-global models such as Hargreaves for daily potential evapotranspiration and Budyko for annual actual evapotranspiration (E-A), as well as the SCS Curve Number procedure for 24-h plot runoff (R-O). Annual R-P is quantified as the difference in annual P, E-A, and R-O. Because the use of non-global models for E-A may induce suboptimal R-P results, ArcB allows corrections of E-A estimates by comparisons with data from a reference station. In a semiarid heterogeneous region in south-eastern Spain, the uncertainty of R-O and R-P was lowered to 4% and 2%, respectively, when correcting E-A. ArcObjects is a versatile programming language which allows advanced users to incorporate more complex formulations for more accurate results as detailed data is acquired and to develop routines for calibration when reference data exist. (C) 2013 Elsevier Ltd. All rights reserved.