A stochastic method to disaggregate rainfall fields into DSD fields is proposed. It is based on a previously presented DSD simulator that has been modified in order to take into account imposed mean values provided at the coarser scale. The integral quantity used to drive the disaggregation process can be the average rain rate, the average radar reflectivity or any variable directly related to the DSD. The proposed method is illustrated and validated using radar rain-rate data provided by MeteoSwiss for both stratiform and convective rain events. The space-time structure of the DSD fields at the fine scale is parameterized using data collected with a network of 16 disdrometers. The rainfall intermittency is modelled using climatological relationships derived from radar data at different spatial and temporal scales. The results show that both stratiform and convective rain events can be correctly disaggregated, although the general agreement in terms of rain rate distributions, intermittency and space-time structures is much better for the stratiform events. Possible extensions and generalizations of the technique (e.g., using radar reflectivities at two different frequencies or polarizations to drive the disaggregation process) are discussed.