عنوان مقاله [English]
Heavy rains every year in all parts of the world, especially in arid and semi-arid regions, cause great damage to the environment and humans. For this purpose, precipitation data of 4 stations of Astara, Bandar Anzali, Rasht (airport) and Manjil from 2021-1993 were obtained from the Meteorological Organization of Gilan Province. Days with heavy rainfall were selected using 95% percentile and were examined for 11/6/2018 due to the brevity of the analysis. Heavy rainfall trend was also evaluated using non-parametric methods of Mann-Kendall, Sense Stimulator and simple linear regression methods. The results of these tests showed that Astara station had a positive, ascending and significant trend, but in other selected stations, despite being ascending, The trend has not been significant. To analyze the representative's day, NETCDF data were obtained from Nova site and maps of sea level pressure, geopotential height of 500 hPa, rainwater, tavaei, wind river, humidity and Huff Müller special humidity were plotted in Gardes software. The maps show that the dynamic clockwise movement in Eastern Europe leads to the flow of westerly and northerly winds towards the study areas, and on the other hand, by placing study stations in front of the landing axis of the bipolar block, which causes rotational and upward movements of the air. And the positive values of Tavaei have proved it, and finally it has led to atmospheric turbulence. The movement of westerly winds has brought the moisture of the Black Sea and the Mediterranean Sea to the atmosphere of the studied areas, especially with increasing wind speed on the day of peak rainfall has increased the amount of special humidity in the lower levels of atmosphere and rainwater.
The importance of precipitation in human societies and all living organisms in general, has caused this climatic phenomenon to be a fundamental issue in climate studies. In terms of geographical location of Iran due to its location in arid and semi-arid regions, the annual rainfall conditions are small, short-term and with severe fluctuations that cause floods and drought at high and low levels, respectively (Asgari et al., 2007 and Quoted from Soltani et al., 2011). Gilan province can be mentioned as one of the important areas in this country where rainfall is a prominent feature. Cloudy and rainy weather is one of the climatic features of this province. Statistical evidence shows that this province is due to the existence of high Alborz mountains in the south; During the passage of migratory rotational systems and the establishment of synchronous patterns and northern rotation, the influx of heavy and super heavy precipitation is not unreasonable; Therefore, suitable conditions are provided for the occurrence of heavier rainfall in Gilan. Ultra-heavy rainfall is one of the various geographical elements that has dangerous life and financial effects that can affect nature and humans (Azizi et al., 2011 and quoted by Zolfaghari et al., 2014). A large amount of rainfall in a short period of time leads to heavy rainfall and gradually to super-heavy rainfall. This phenomenon causes a lot of damage in most places at the time of the event, especially in low-rainfall areas (Arabi, 2000, quoting Khorshid Doust et al., 2016). There is no complete definition of heavy and super heavy rainfall that can be used equally for all different areas, because in each area, depending on the physical, local and synoptic conditions, a certain amount of rainfall can cause a flood. In the popular definition, rainfall that occurs in the region more than 30 mm per hour is called heavy rainfall. It is one of the oldest studies on heavy rainfall conducted by (AII this 1948). He concluded that at the 500 hPa level, landings within the positive rotation forward range caused more intense rainfall. (Maddox, 1978) In a synoptic comparison between the heavy floods of Rapids City and Big Thompson, it was concluded that the main cause of this type of flood is winds that blow at low levels and cause high humidity to reach these two areas. Roughness also causes climbing and eventually heavy rainfall. (Aboutaleb et al, 2007) examined the changes of the annual series of relative humidity in Jordan. Their work showed that there is a significant increasing trend in the annual series of relative humidity. (Bourdieu et al, 2007) investigated the amount of Farin wet and dry periods for the island of Sicily. (Carbolut et al, 2008) In the Samsun region of Turkey, during their studies on the trend of precipitation and temperature, they concluded that there is no significant positive and negative trend between temperature and precipitation (Sen Roy, 2009) in India to study patterns Farin rainfall has shown that the high altitudes of the northwestern Himalayas cause heavy rainfall. (Lupi et al, 2010) A study was conducted over a period of 55 years (1951-2006) of seasonal rainfall in southern Poland, eastern and central Germany. According to their findings, the trend of increasing rainfall is observed in all seasons of the year, but in Poland this trend is reversed. These characteristics are more established in winter.
The purpose of this study is to investigate the statistics and synoptic of super heavy rainfall in Guilan province, during which data related to daily rainfall (24 hours) of Astara, Bandar Anzali, Rasht (airport), Manjil stations of Guilan Meteorological Department in a period of 29 years ( 1371-1399) was extracted. In the present study, the ultra-heavy precipitations of each station have been filtered in 95% percentile according to the topographic conditions and its geographical location. Among the main methods of this research, the non-parametric method of Mann-Kendall and Sens-Eastmotor statistical tests and the simple linear regression method were examined and analyzed to prove its significance or not. Finally, 11/6/2018 was selected as the peak day of precipitation and the modeling of synoptic systems was studied. For this purpose, upper atmosphere data from the National Environmental Prediction Center (NCEP-NCAR) were used to draw and analyze the day of heavy rainfall and the day before. These maps include sea level pressure, 500 hPa geopotential level, rainwater at ground level to the upper atmosphere, Tavaei level at 500 hPa, 250 hP wind and humidity at 500 hPa, especially in Hoffmol. Gardes software was drawn.