مجله مخاطرات محیط طبیعی
پیاپی 4 (بهار 1393)

In this study the temporal and spatial patterns of drought with the use of daily precipitation data of 30 synoptic weather stations for common period of forty years, and for five temporal series (3-, 6-, 12-, 24- and 48-month) by using SPI index, with three characteristics of intensity, frequency and duration on a national scale were investigated. The results show drought's maximum frequency in the 3- and 6-month scale in the extremely dry category is Sanandaj Station. In the 6-month scale in the moderately dry category is Ahvaz Station, in the severely dry category is Noshahr Station, and in the extremely dry category is Sanandaj Station. In the 12-month scale in the moderately dry category is Orumieh Station, in the severely dry category is NoshahrStaion, and in the extremely dry category is BabolsarStaion. In the 24-month scale in the moderately dry category is Bandar Abbas staion, in the severely dry category is Noshahr Station, and in the extremely dry category is Ramsar Station. In the 48-month scale in the moderately dry category is Bandar Abbas station and among of two other stations, Noshahr Station has the drought's maximum frequency. Moreover, the highest intensity is occurred in Semnan Station in the 3-monthscale with amount of -3.89.

Despite the extensive studies on geomorphological phenomena in Iran, since investigation of meteorite impact craters h not been considered. Based on both remote sensing technique and field work we have recognized the circular structure of Zirouki crater in the Samsour desert, southeast of Iran, which is claimed by MansouriDaneshvar and Bagherzadeh as possible impact crater on 2011 and 2013. The Zirouki crater is defined as one of potential impact sites by Baratoux et al, (2012) and registered as first possible impact carter of Iran in Expert Database on Earth Impact Structures (Web Encyclopedia on Natural Hazards, Novosibirsk, Russia). When the crater confirmed as an impact structure then would be the third impact structure candidate in the Middle East after the Wabar craters in Saudia Arabia and Jebel Waqf as Suwwan in Jordan. Investigation of the possible impact structure of Zirouki crater was done using the geomorphological interpretations in different levels of topographical, geophysical, geological and petrographical studies. The main results of the present study revealed that quite obvious crater shape morphology with mounded rims and a central uplift projection; as well geophysical pattern provided very strong evidence for possible impact structure, indicating the presence of circular negative gravity anomaly at the whole of the craterwhich distinct it from igneous patterns and other erosive forms.

Heat island forming in big cities is one of the modern environmental hazards due to the uncontrolled urban development. The global temperature is increasing slowly from the 19th century. The heat islands of big cities have two components: global warming and urban development (population growth, urban development, land use changes and etc.). The purpose of this paper is to study these components in Mashhad city with 127 years of long-term temperature data. Change point of Mashhad annual temperatures was achieved with Grey relational patternin 1980. Mean annual temperatures before and after 1980 are respectively 13.5 and 15.1 by difference 1.6 which shows increasing trend. This increasing is about 3 degree end to 2013. The linear trend line equation for Mashhad after change-point has coefficient of determination and the trend test statistic is 0.0993 (show trend), While this statistic before change point is 0.0035 (show no trend). Moreover annual temperatures of three stations: Kortian, Bar and Olang-Asadi which located outside of Mashhad and adjacent to it analyzed for comparing heat island too. The grey relational pattern showed that change points of the three stations are between the years of 1976 to 1980.This analysis showed that the increasing in annual temperature of Mashhad and suburb are nearly at the same time.The slop of Mashhad's trend line compared with Olang-Asadi. The reason of choosing Olang-Asadi is that its elevation similar with Mashhad and it is being adjacent to Mashhad.The final result showed that the heat island in Mashhad began from 1981 with a slope of 0.093. The annual difference temperature of Mashhad is degree from 1981 to 2013. The relation of temperature difference and population growth provided to a standardized pattern that confirms the existence of heat islands.

This study aimed to identify the cause of intense rainfall occurred on April 30, 1994 in Kermanshah, The maps of surface pressure in the upper atmosphere Sudan and low pressure systems result in precipitation patterns were identified The role of this system as one of the major systems of the West was to climax. Maps and atmospheric pressure at the upper and lower levels, it was determined that Starting with the establishment of precipitation over the Mediterranean trough Turkey and Iraq and the location of the study area at the front of the upper levels, Sudan is associated with low pressure at the surface occurs. There is a high pressure system over the Arabian Peninsula and North-West Indian Ocean This system leads to amplification. Omega plans and volubility of the story of instabilities weather is rainy day. The moisture content of the maps, Most moisture levels 850 hPa and the Mediterranean Sea to be supplied the region is imported from the West. But the 700 hPa level is the main source of water that flows from the Red Sea to the south west of the study area appears.