Radiological environmental impact assessment models are important tools for public and environmental protection, for example, in planning measures to be taken in the event of accidental releases. This publication was developed to report on results from international model validation exercises conducted within the IAEA's MODARIA I programme to test and improve the modelling for predictions used for environmental transfer and dose assessment in urban areas. Model exercises were focused on: contamination densities and activity concentrations in air following short range atmospheric dispersion and deposition events; prediction of atmospheric dispersion and application of decision support systems under complex meteorological and topographic conditions; and expected reductions in ambient dose rates and activity concentrations due to protective actions following a nuclear accident. The report builds on past IAEA publications and provides relevant examples for use in strengthening the global nuclear safety framework as part of emergency preparedness and response planning following a nuclear or radiological emergency.