Depth-Duration-Frequency (DDF) curves are a probability map for rainfall annual maxima in a given site. For a given return period T [years], the corresponding DDF curve gives the raindepth threshold h_T [mm] which is exceeded with frequency 1/T, as a function of event duration D [hours].
DDF curves are traditionally estimated on a particular observational site from the time series of rainfall annual maxima there recorded. A parameter estimation is performed on the GEV (Generalized-Extreme-Value) distribution, and the GEV parameters are inserted into a more or less complicated analytical expression for the DDF curves. The "spatial bootstrap" approach (Uboldi et al., 2014) performs parameter estimation on a geographic area by making use of all relevant data at each target point, combining regionalisation and spatial variation.
Works on rainfall annual maxima statistics:

• F. Uboldi, A. N. Sulis, C. Lussana, M. Cislaghi and M. Russo, 2014. A spatial bootstrap technique for parameter estimation of rainfall annual maxima distribution. Hydrology and Earth System Sciences, 18, 981-995, doi:10.5194/hess-18-981-2014   Link
• presentation at EMS 2013: F. Uboldi, A. N. Sulis, M. Cislaghi, C. Lussana, and M. Russo, 2013. Systematic errors and time dependence in rainfall annual maxima statistics in Lombardy. Presentation at EMS 2013, 10-14 September, Reading UK.

Parameters and quantiles estimated by means of the spatial bootstrap technique are available to users in the web-GIS (Geographic Information System) of the hydrographic service of ARPA Lombardia (there, follow: "Linee segnalatrici 1-24 ore - P.STRADA")

SEMINAR 02 May 2016 at ARPA Emilia-Romagna Bologna, Italy: "Variazioni dei massimi di precipitazione in area prealpina — Evidenza di cambiamento locale nel tempo della climatologia dei massimi annuali di precipitazione" (mostly in Italian: Time variation of precipitation annual maxima in prealpine area in Italy)

Besides, you may also want to have a look at maps of hourly and 24h-accumulated precipitation obtained as analysis of raingauges observations and integration of raingauge observations and weather radar estimates (sorry, these web pages are in Italian).