چکیده:
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.
خلاصه ماشینی:
Noohia a Faculty member, Atmospheric Science and Meteorological Research Center (ASMERC), Iran Received: 2 October 2009; Received in revised form: 11 August 2010; Accepted: 3 January 2011 Abstract 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 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.
2. Materials and methods Statistical procedures for estimating PMP may be employed wherever sufficient precipitation data are available, and are particularly useful where other such meteorological data as dew point and wind records are not available.
Climatological elements that are applied in estimation of PMP values in physical method are: -Dew point temperature (mean monthly, mean ten day and maximum 12-hour) -Wind speed and direction (mean monthly, mean ten days and maximum 12-hour) -Pressure (mean air QFE1 pressure) -Precipitation (maximum 24-hour) -Synoptic maps of sea surface and upper levels in stormy days.
Then, by using equation (1) humidity coefficients were calculated: FM=Wm/Ws (1) Where: Wm is the maximum precipitable water at 1000 to 200 millibar levels which can be obtained on the basis of maximum 12-hour duration dew point with 100-year return period in a simultaneous period with storm.