Seasonal Analysis of Days of Heavy Rainfall in Talesh-Anzali Basin

Heavy Rainfall are one of natural dangers. Heavy rainfalls, directly or indirectly, affect human lives and their activities. In this study Talesh-Anzali wet land basin in the west of Guilan province has been investigated. To determine the probability of heavy rainfall events (seasonal) and the trend existence, non-parametric Men-Kendall test, to determine the probability of rainfall event 30mm Poison’s method and to identify local patterns of precipitation event IDW method have been applied. The data in this study include daily precipitation of 30mm in 20 synoptic stations in a period of 30 year (1987-2016). The results showed the trend is mainly increasing, so that the stations located in the center towards the north of the study district in every four seasons and the stations in Anzali in spring and Masoleh in three seasons of summer, autumn and winter have increasing trend, but in some cases, some stations mainly toward the south half of the area such as kasma in summer, Bashmahalleh and Rasht in winter and Ghalehroudkhan in autumn and winter have extreme decrease trend. Also, in all seasons of the year, in some stations, irregular and accidental changes are observed in the event frequency. This irregularity results from lack of continuity increase or decrease of the event frequency and rainfall or lack of rainfall of 30mm in some stations. Poison’s distribution showed that the probability of lack of event in stations with non-humid climate is so high and addition of lack of event with an event is more than 90% frequency of rainfall event 30mm. Furthermore, in the north and central stations of the region, the most possibility for different events in all seasons of the year has been recorded. In the end, the results showed Poison’s distribution has a proper evaluation of precipitation events in this region.