The analysis of maximum precipitation is usually carried out by using IDF curves (Intensity-Duration-Frequency), which in turn could be expressed as MAI curves (Maximum Average Intensities). An index “n” has been developed in this work, defined from the exponent obtained when adjusting IDF climatic curves to MAI curves. That index provides information about how maximum precipitation is achieved in a certain climatic area, according to the relative temporal distribution of maximum intensities. From the climatic analysis of index “n”, large areas could be distinguished in the Iberian Peninsula, characterized by rain maxima of a stormier origin (peninsular inland), and areas characterized by rain maxima of a more frontal origin (southwest, Atlantic coast and Mediterranean coast). Additionally, these areas could be more specifically divided according to the persistence of maximum precipitation.