Comparative Study of Multi-Day Intense Precipitations over Iran

Precipitation is one of the meteorological variables that have highest spatial and temporal variability. There is increasing attention to variations and trends of extreme values of such a variable in local, regional and global scales. Extreme events of precipitation have caused serious effect on human lives and properties. In this paper, we examine extreme precipitations in view of monthly maximum 1-day (Rxlday) and monthly maximum consecutive 5-day (RxSday) precipitations over those Iranian synoptic stations having reliable data. These indices can also be defined seasonally, but seasonal indices are more spatially coherent than the annual indices, spatial coverage remains generally poor in global scale. We mainly worked on 16 Synoptic stations that are distributed well over the country. Highest 1 day and 5 days precipitations among the stations under study are 353 mm from Bandar Anzali on September 17th, 1962 and 487 mm from Ramsar on 2-6 October of 1993 respectively. Lowest ones are 41 mm from Bam on January 26, 1991 and 5 1 mm from the same city on 20-24 January of 1957.We got negative trends for Rx5day in NW, West of Zagros mountain ranges, Caspian Sea coastal area, NE, SE and some stations located in the south of Iran. We did not find a clear pattern for Rxlday over the Country. Whole Country actually showed a mixed pattern. We also got significant negative trends for this index for Shiraz and Zahedan, and a significant positive trend for Abadan at 0.05 significant levels.

Keywords:

1-day extreme precipitation , 5-day extreme precipitation , Extreme event and trend