Climate change is expected to effect Storm runoff and erosion processes in Mediterranean watersheds at multiple spatial scales. Models are typically applied to estimate these impacts; however, the scarcity of spatially distributed data for parameterization, calibration and validation often prevents application of these models, particularly for larger catchments. This report, the first part of a two-part article, presents an application and evaluation of the MEFIDIS model for two Mediterranean meso-scale watersheds (115 and 290 km(2)) in a data-scarce environment. A multi-scale assessment method was used that combines quantitative validation and qualitative evaluation, consisting of three steps: (1) calibration at the small (field) scale using results from rainfall simulation experiments: (2) calibration and validation for catchment-scale results while changing catchment-scale parameters only (channel roughness and a parameter controlling the distribution of saturated areas); and (3) qualitative evaluation of within-watershed erosion processes using empirical estimates of sediment delivery ratio and gully location. The results indicate that calibrating MEFIDIS at the field scale can provide reasonable results for catchment runoff and sediment export and for within-watershed erosion processes. Copyright (C) 2009 John Wiley & Sons, Ltd.