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Mr Ali Hasanzadeh, Mr Hooshmand Ataei, Mr Nader Parvin, Mr Amir Gandomkar,
Volume 6, Issue 1 (5-2019)

Agricultural crops have damaged a lot due to the aftermath of late spring frost, and because low temperatures have damaging effects on agricultural production, it is essential to anticipate and prevent potential damages. Often, atmospheric temperature variations are very urgent due to the high temperature of the systems and the plants cannot adapt themselves with severe oscillations and, have been damaged. The aim of this study was to analyze the climate of the spring frost in Kermanshah, identifying the sea level equations and the late spring freezing frost of the period from 1990 to 2015. This survey has been done to determine the period of the freezing phenomenon, determine the minimum daily temperature of 7 stations placed in Kermanshah,  Hamedan, and Ilam. After analyzing the data of spring frost freezing of Kermanshah province using the main component analysis technique and hierarchical clustering method, the most common 10 patterns of late spring coldness of the area were studied and determined. In 10 resulting cluster, 8 clusters were related to the high-pressure pattern of Siberia. From the total 91 days of spring frost freezing in Kermanshah province (79% (72 days)) is due to the high rainfall of Siberia, 12% (11 days)  is due to the Mediterranean climate and 9% (8 days) is due to the Van lake climate. These pressure patterns were named according to the location of their deposition, which caused the loss of the environment and the freezing frost of the spring.
Khabat Derafshi,
Volume 7, Issue 3 (11-2020)

In this study, the risk map as an index to define the said complexity was prepared in 5 categories of risk by combination of Tehran metropolis flood hazard and vulnerability maps. To analyze the risk varieties, the hydrological catchments of Tehran were extracted by Arc Hydro model and 12 catchments were selected. Using land use, roads network, and the percentage of residential floor area, bridges, altitude, slope and drainage density variables, the flood hazard map was calculated. Dilapidated urban blocks, population density, land use, bridges, slope and drainage density layers were used as variables which affecting the flood vulnerability. Covariance index was applied for matched variables and considering the locational coherence between the values of them. Based on the new raster layers, flood risk variability in Tehran metropolis as well as in each of the catchments were analyzed using stepwise regression model. Explanation of locational changes of risk between the catchments needs to calculate the weighted average risk and the independent variables in 12 catchments that obtained by zonal statistics. Based on these average values the factor analysis used to determine the varifactors or main components of the variability in flood risk between the catchments. Finally, fractal geometry models (perimeter-area and cumulative number-area) were used to demonstrate the chaos of the flood risk value in 5 categories of risk. According to the flood hazard zoning map of Tehran metropolitan area, the extent of high hazard zone is 129.6 square kilometers. High risk zone covers 28.6% of Tehranchr('39')s area, indicating that most of the citychr('39')s extents (174.4 square kilometers) are located in the high flood risk zone. After that, the moderate hazard zone is 28.5% of the city area. Very low zones with 3.53% of the total area are the smallest zones in the city, which are only 21.5 square kilometers. Overall, 78.3 percent of the total area of the city is located in the moderate to very high zones of flood hazard, reflecting Tehranchr('39')s challenge to flooding. The vulnerability map defines that 138 km2 of the Tehran city area is located in high and very high zones of the flood vulnerability. According to Tehran metropolitan flood risk zoning map, 163.1 km2 of Tehran city area is located in high risk zone which has the highest rate among flood risk categories in Tehran metropolis (26.9%).

- Mahmoud Roshani, - Mohammad Saligheh, - Bohlol Alijani, - Zahra Begum Hejazizadeh,
Volume 8, Issue 4 (1-2021)

In this study, the synoptic patterns of the warm period of the year that lead to the cessation of rainfall and the creation of short to long dry spells were identified and analyzed. For this purpose, the rainfall data of 8 synoptic stations were used to identify the dry spells of the warm season for 30 years (1986 to 2015). The average daily rainfall of each station was used as the threshold value to distinguish between wet and dry spells. Then, according to the effects of dry spells, they were defined subjectively and objectively with different durations. Thus, 5 numerical periods of 12 to 15, 15 to 30, 30 to 45, 45 to 60 and more than 60 days were identified. By factor analysis of Geopotential height data at 500 hPa, 4 components were identified for each period and a total of 20 components for 5 dry spells. Therefore, 5 common patterns control the stable weather conditions of dry spells. Most dry days are caused by subtropical high-pressure nuclei, which have a wide, even, dual-core, triple-core arrangement. The effect of subtropical high pressure on the dryness of the southern coast of the Caspian Sea is quite evident. Other dry days were caused by southerly currents, weakening of northern currents, and the trough Anticyclones’ area. Also, the anomaly map of the components days at the 500 hPa level showed that the anticyclones and cyclones correspond to the positive and negative phases of the anomalies, respectively.

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