Comparison of physical and statistical methods for estimating probable maximum precipitation in southwestern basins of Iran

The probable maximum precipitation (PMP) is the greatest depth of precipitation for a given duration that is physically possible over a given size storm area at a particular geographical location at a certain time of the year. In this study a physically based method was compared with a statistical procedure to calculate PMP in the southwest arid regions of Iran. In order to estimate PMP using a physically or meteorologically oriented method, such climatological elements as precipitation, dew point temperature, and wind speed were studied in seven synoptic stations in the region. Synoptic maps of appropriate time scales were also studied. Then widespread and severe storms with various durations were selected and Depth-Area-Duration (DAD) curves for all the selected storms extracted. Using the physical method, PMP estimations were obtained at different locations and then the results applied to areas of 1000, 5000 and 10,000 km2. PMP estimations were also obtained through statistical analysis of the series of annual maximum 24 hour precipitations. The result showed that the values obtained through statistical procedures are more than two times those of meteorological method, for all the stations. Comparison of estimates indicated that least difference between two methods belongs to Abadan and the most difference to Bushehr, the magnitude of PMP in physical method is 39.2 and 22.8 percent of statistical method, respectively. Thus using statistical method for an estimation of PMP in the region leads to unacceptable consequences for a construction of water structures.