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Flash floods caused by extreme rainfalls are one of the most significant natural hazards. In the present study, the precipitation data of 69 meteorological and climatological stations with temporal intervals were obtained to determine the threshold of extreme precipitation as well as analyzing its significant patterns in the western regions of Iran. To determine the threshold of extreme precipitation, the theory of extreme value method was applied. In this method, precipitation of 22 mm and more than that covers 30% of the area had been identified and extracted as extreme precipitation. Therefore, 119 extreme precipitation events during the study period had been identified. Then, four patterns were analyzed using cluster analysis. After that, network data of geopotential height levels of 200, 300, 400 and 500 hPa for these days, from re-analyzed data series of NCEP/NCAR in the range of 10°-80°E and 0°-70°N and in 13,460 cells 2.5° × 2.5° were extracted by GrADS software. The results of the study showed that the most important humidity source for precipitation was the Mediterranean Sea, the Black Sea and the Red Sea, respectively. The upward vertical speed at different levels, located on the east and southeast cyclones of upper levels, which matches low pressure of the Earth's surface, indicating unstable conditions in the region. Also, placing cutoff lows due to westerlies activities with warm and humid air advection at the surface and upper-level cold air were the main causes of severe atmospheric instability in the west of Iran. KeywordsExtreme precipitation • Threshold • Jet stream • West of Iran (WOI)

Due to the importance of pollution monitoring in marine ecosystems and lack of a coherent and systematic investigation of heavy metal ions along the southern shores of the Caspian Sea, in the present study, the amount of these metals and As ions in coastal waters along its 780-km-long coast in Iran have been studied. Heavy metals (cobalt, nickel, copper, zinc, cadmium, mercury, lead) and a poisonous metalloid (arsenic) were selected in 59 sampling stations and determined using differential pulse polarography method. The multivariate statistical tools were applied to describe and interpret the experimental data. The overall mean concentrations of studied metals (in microgram per liter; μg L) in the samples were found in the order Zn (10.9) > Ni (7.4) > Cu (5.5) > Pb (1.9) > Hg (1.4) > As (1.3) > Co (1.1) > Cd (0.2). The results when compared with reported international standards confirmed that the sampled waters do contain some of these elements above the suggested maximum permissible limits. Hg and Cu were detected in 54.2 and 72.9% of the samples, almost all above the permissible limits. Ni, Zn, Pb, and Co were detected in 100, 96.6, 93.2, and 88.1%, respectively, while 8.5, 22.0, 3.4, and 1.7% were above the permissible limits. Cd and As were present in 61 and 93% of the samples, and their concentrations were higher than the rate presented by Russian System of Management Chemicals (RSMC). In addition, spatial distribution of heavy metal concentrations showed that Gorgan Bay is an ecosystem serving as a filter, trapping natural and anthropogenic materials that are brought from industrial, commercial, and urbanized areas. The multivariate data analysis reveals that Caspian Sea is contaminated by both anthropogenic as well as pedo-geochemical sources.

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Nitrate enters surface and ground waters from the decomposition and corruption of human and animal wastes, industrial products, and runoff from agriculture [2]. It harms the digestive system, causes mouth cancer, creates congenital anomalies on the fetus, increases the size of thyroid gland, creates goiter, increases blood pressure, leads to the emergence of insulin-dependent diabetes, and reduces physiological-and neurological performances [3].