Regionalization Of the Rainfall Temporal Patterns,Less Than 6 Hours In Iran

Storms, as the main cause of producing floods, runoffs, soil erosion and the like, have important specifications which affects differently on the resulting floods. Temporal patterns are functions of rainfall intensity in time. These patterns in their one-peak states are estimated by triangle. If the length of the storm peak point is given, then the triangular shape of the storm intensity function for the basin is available. In the present study, a new profile for storm intensity function in different regions in Iran is considered and according to other important specifications such as rainfall amount, rainfall duration, and storm peak intensity, the storm peak time is measured in a nonlinear relationship. The total number of storm gauging stations throughout Iran is 396. The number of the acceptable stations in terms of the rainfall duration less than 6 hours is 130. According to maximum daily precipitation, Iran is regionalized to 7 areas. A sample of each area’s storm with different duration is selected by systematic sampling method. The results showed that the storms with duration less than 6 hours behave properly in all our regions and about 43.6% of them have one-peak. About 34.6% of the total storms in Iran have one-peak and contain 10 to 48 hours duration. In this study, the analyzed storms had one-peak and less than six hours duration. Through linear and nonlinear regression and multiple regressions, the relationship between peak-time and other storm specifications was gained for all the regions in Iran. The most fitted patterns were nonlinear (log-regression) patterns. These patterns include 3 log-regression variables, namely duration specifications (Td), the proportion of rainfall amount (P) to rainfall intensity (IP), for regions 1 to 5. The best pattern for regions 6 and 7 was gained through 2 log-regression variables according to rainfall duration. Comparison of the presented patterns in this study showed their advantageous over other patterns which had been suggested so far.