The majority of rainfall measurements in the world is at the daily scale. Unfortunately, 24 h annual maximum rainfall depths, which refer to a period starting at any instant, are more useful indicators. In this work we investigated the possibility of reconstructing 24 h sliding maxima from historical daily maxima over the Po basin (Italy) by means of a parameter named Hershfield factor. The application of this factor improves the knowledge of the spatial variability of rainfall extremes.