Probable Maximum Precipitation for 24 Hour Duration over Four Central Provinces in Iran

Probable maximum precipitation (PMP) is a common way to synthesize corresponding probable maximum floods (PMF) to design large hydraulic structures in short-data cases. The PMP for many stations in Iran and other places using the Hershfield formula is routinely estimated as the mean plus 15 standard deviations processed from one-day yearly maximum rainfall values. However, the value of 15 may not be suitable for all stations with different climatic specifications. In this paper, yearly maximum one day rainfall data of 23 synoptic and climatology stations in the four central provinces of Iran were analyzed in an attempt to estimate PMP for a one day duration based on an appropriate frequency factor. Based on the actual maximum daily rainfall data of these stations the highest value of frequency factors was found to be 7.63 for one day duration. The frequency factor obtained for each station was subsequently used to estimate one-day point PMP values. The mean ratio of one-day PMP values to the highest observed one-day rainfall was about 1.3 over the study area. The PMP maps are considered important tools to determine reliable and consistent estimates for any location in the area for large hydraulic structure designs. Using these PMP estimates a generalized pattern for the spatial distribution of one day PMP could be demonstrated.