jalal behzadi - Department of Agriculture and Natural Resources, Lahijan Branch, Islamic Azad University, P.O. ۱۶۱۶, Lahijan, Iran

Minimum and maximum precipitation and their oscillations in a specific period of time is a common phenomenon all around the world, which depend on the type of climate. With the climatic variety present in Guilan province, precipitation oscillations are so complicated compared to the average. Precipitation data were collected from weather stations of the Guilan Regional Water Authority and the Meteorological Organization, and they were then reconstructed using the Minitab software. Using the statistical analysis, the minimum and maximum precipitation of twelve stations were estimated, and next to the thirty-year recurrence interval was calculated using the HYFA software. Due to the number of data and stations, the five weather stations of Manjil, Lahijan, Rasht, Rudkhan Castle and Anzali were picked out using the clustering method, and the map of precipitation and their area was created using the GIS. Anzali and Rudkhan Castle stations possess the highest precipitation in their statistical period, while Manjil possesses the lowest amount of precipitation in the whole province, and suffers from more water shortage and aridity compared to other stations. Lahijan and Rasht stations can be classified as stations with medium precipitation, i.e. both conditions equally affect the area. The authorities should be more careful and sensitive when making plans for this region. Unbalanced oscillations and highly severe recurrence intervals must be considered in environmental, agricultural and tourism planning, to reduce the potential losses resulting from strong and weak precipitation, and to prevent the failure of various projects due to lack of correct information and plans.

climate, the return period, Guillen, precipitation