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Firooz Mojarad, Razieh Kheiri, Zahra Noorisameleh,
Volume 14, Issue 35 (3-2015)
Abstract

Iran's Potential for the occurrence of drought at various severities illuminates the need to examine this phenomenon with new indexes. The major deficiency of the current indexes is that they cannot monitor the droughts in daily scale. Effective Drought Index (EDI) overcomes this defect. The goal of this study is to analyze the frequency of daily droughts by EDI in 43 synoptic stations in a 30-year period. Accordingly, the frequency of daily droughts in the stations was calculated by EDI during the seasons and the year. Then the stations were divided into five groups using cluster analysis based on total frequency of mild to most severe droughts (categories 1 to 4), and frequency patterns in each group were examined. The results showed that the most severe droughts have not happened in the stations except for Gorgan, Zanjan and Torbat-Heydariyeh. In contrast, the frequencies of mild, moderate and severe droughts, all being equal, are much more than most severe droughts, and their frequencies are almost equal. In 56 percent of the days, a variety of droughts (mild to most severe) has occurred in the whole country. Based on the output maps, frequency distribution of droughts in the country does not follow a certain geographical pattern, so it could be cocluded that all types of droughts have happened in all regions of the country. However, maximum total frequency of daily droughts (mild to most severe) is observed in the east and center parts. The decrease in the EDI values over time shows the tendency of the most stations towards drought.

Fariba Sfandyary Darabad, Mansour Kheirizade, Masoud Rahimi,
Volume 22, Issue 66 (9-2022)
Abstract

Floods are one of the most abundant and destructive natural disasters that every year are caused heavy losses of life and property. Due to human activity in river systems and construction in rivers, flood damage has an upward trend. One of the most important actions to reduce flood damage is the provision of flood hazard zoning maps and their use in spatial planning. In this study, the risk of flood in the Nirchay River Basin that located Ardebil province was investigated. For this purpose, the HEC-HMS model was used to simulate rainfall-runoff and to identify flood zones and fuzzy logic in order to overlay the layers and prepare a flood hazard zoning map.The simulation results show the high performance of the HEC-HMS model in simulating rainfall-runoff of the Nirchay River Basin and estimating peak flood discharges. Rainfall conversion to runoff at the Nirchay River Basin controlled by slope and land-use.The most runoff height and peak flow in Nirchay River Basin are located in the upstream sub-basins. This is due to the steep, low permeability soil, frequency impervious surfaces and high CN. The combination of layers using fuzzy logic has shown that about 8.6% of the surface of the basin are located with a high risk of flooding. These zones are located mainly on the floodplain of the Nirchay Basin. Due to the Low valley width and low slope, these lands are always at flood risk. Most settlements in the study area are located at downstream of the basin. This has increased the risk of flooding.
 

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