عنوان مقاله [English]
Rainfall time pattern has a marked influence on design of dams, urban runoff collection systems, culverts, drainage systems and or determining, flood potential and soil erosion. In this research, data of 18 rainfall autographic stations of Khorasan province of Iran were used to implement the rainfall time pattern. Rainfall depths were extracted for each time interval from rainfall charts and were categorized to four quarters. A ranking method was used to arrive at rainfall time patterns corresponding to time intervals of 1, 3, 6, 9, 12, 18, and 24 hours. After normalizing the rainfall mass curves, every quarter of rainfall was ranked, where rank 1 was given to the highest. The final pattern was derived by averaging the quarter ranks and percentage of rainfalls corresponding to each duration. A contingency table was used to verify the independency of rainfall time patterns by a chi-square test. The results showed that in Khorasan province: a) most of short duration rainfalls are first quartile, b) most long-term rainfalls are second quartile, and c) on overall more than 50% of rainfall amounts for nearly all rainfalls in this arid and semi-arid region occurred in the first half of their period.