This paper concerns an investigation of evaporation, infiltration and detention storage on paved surfaces and the effect of surface texture and microtopography on these processes. A numerical model has been developed which represents the evaporation and infiltration processes on a nominally impervious surface as well as the depression storage due to the surface microtopography. The model was applied to semi-randomly generated surfaces and the results show the relationship between surface microtopography and initial storage losses.