مجله مخاطرات محیط طبیعی
پیاپی 12 (تابستان 1396)

In terms of climate, Iran is an arid and semi-arid country, where vital water resources in this country are highly dependent on atmospheric precipitation. Understanding the characteristics of climatic dry periods such as frequency, severity, and duration of periods is important in environmental planning. In this regard, characteristics of the country's dry climatic periods based on "dry days after the last day of the rainfall" (DDSLR) using statistical data of 48 synoptic stations in Iran over a 30-year period from 1979 to 2008 were studied. DDSLR index trend changes with a probability of 25, 50, 75 and 90 percent (optimistic, average, pessimistic and very pessimistic) as an indicator of the severity of the drought periods of low, medium, high and very high determined for each of the stations and dry period features including start, stop, frequency, and duration of driest days was determined for each station. Finally, based on the length of dry period and through interpolation method Kriging zoning maps for the entire country was drawn. The results showed that climatic dry periods in stations of southeast of the country, especially port stations such as the Oman Sea (Chabahar and Bandar Abbas), before other stations begin. Also dry period ends earlier in the Caspian Sea coast stations. The shortest period of drought on the northern coast of the country and the longest period of drought occurs in the southeast of the country. The driest days at most stations will happen in October. It also turned out that with an increased probability of 25% (probably optimistic) to 90 percent (likely very pessimistic) the area has a very long period of drought in parts of the south; southeast and northwest of the country will increase.

Blocking can be effective in Occurrence of damaging climatic hazards. In order to investigate the role of blocking in the event of heavy snowfall and persistent 31January 31 to5 February 2014, maps Average air pressure at sea level, 850, 500, 300, layer thickness map between 1000 and 500, the position of zero degree isotherm at ground level, U-Wind, V-Wind, Omega (Vertical Velocity, relative humidity, temperature and potential temperature are analyzed. The results showed that Iran is located influence strong and deep right, blocking trough of Omega has a very strong ridges width of 70 degrees north. With the falling of cold air from higher latitudes along with strong high pressure center located in the Caspian Sea with 1050 hpa pressure, With plentiful moisture and temperature conditions especially at the level of 500 and 850 hpa, Regarding the nature of blocking and quasi-stationary conditions continue for 6 days, most parts of Iran was accompanied with snow and some areas due to their position and other conditions were exposed heavy, sustained snow. Investigation the dynamic components showed that in adulthood blocking these components reached its peak and led to continuous heavy snow in most parts of the country. Identification blocking systems that led to heavy snowfall prediction using maps and issue timely early warnings can help planners and decision makers affected areas to prepare for and prevent further damage.

Drought is a climate phenomenon with a lack of moisture and rainfall compared to normal conditions. This phenomenon strongly affects all aspects of human activity. In this Article, were discussed the drought situation in Urmia Lake using MATLAB software and system capabilities combined indicators SEPI on two-time scales 6 and 12 months. Therefore was used climate data of temperature and precipitation for 5 synoptic stations basin of Lake Urmia (Tabriz, Maragheh, Urmia, Saghez, and Mahabad). Results indicated that SEPI index show features of SPI and SEPI index. As well as it enters temperatures as a powerful factor in the drought severity in order to the investigation of the drought conditions; So SEPI drought index is better than the SPI for the study of drought. Drought studies on SEPI index indicated that drought trend in Urmia Lake Basin is increasing. The temperature has an increasing trend with more intensity. The longest duration of drought in the basin of Lake Urmia is in Urmia station on a scale of 6 months from May 2005 to November 2006 for 19 months. The highest percentage of drought observed in Urmia and the lowest percentage in Mahabad stations.

Drought is natural phenomenon’s which can damage were and has a significant loss to human and natural structures. The occurrence of this phenomenon cannot be predicted with complete certainty. The main objective of this study is clustering of drought tradition stations and assessment Climate drought based on the triangular relationship between drought and Hydrometeorology and meteorology variables Such as rainfall, solar radiation and sunshine hours. In this study, using data from meteorological synoptic stations in Iran where twenty solar radiations were recorded, was conducted in the period 1970-2010.The stations studied using Minitab17 software based on the standardized precipitation index solar radiation and sunshine duration, Clustering, Standardized monthly precipitation and from each cluster a station were selected and to examine the relationship between drought and solar variables, and to examine the relationship between drought and solar variables the standardized precipitation same value curves map was drawn and then Angstrom equation variables such as solar radiation and sunshine duration as reference variables was drawn. The results showed solar variables divided into eight different Clusters in all studied stations coefficient of Angstrom equation 0.62-0.96 determinate except Bojnoord, Ramsar and Shiraz are 0.038, 0.067 and 0.36, respectively. The statistical mean period shows most station that started in March and continues in June, July, September, and October and continues in the late of November. In this period, the most sunshine hours and sun radiation are recorded.

In this research was assessed the climate change in 2011-2030 periods with A2 emission scenario by using of AOMCM models and uncertainty related that for this purpose were utilized of 6 models in Rineh and Baladeh stations. Climate change is effective on, river flow shortages, floods, and the declining water system that with predicting the climate change can perform fair management of water resources. The Haraz Watershed with 4012 square kilometer area is located in Mazandaran Province. To assess the impact of these changes on the watershed outlet, SWAT hydrological model was used. This model is sensitive to changes in terrain and weather. The time horizon 2000-2014 was used in order for calibration and validation the model. Then, after ensuring the performance of the SWAT model, the downscaled climate change data were determined by the study models for each climate factors input to SWAT model runoff change in future periods were assessed. The climate model results showed that the annual minimum and maximum temperature will be increased 0.7 ° C and 0.62 respectively. The average annual rainfall for the study area will be decreased at a rate of 18 percent. Compare current flow simulation showed that the peak flow for the future period will increase nevertheless the average flow discharge will decrease in the amount of 12 percent. Therefore the climate change should be considered in order to tackle with environmental hazards and Long-term planning.

Rapid population growth and physical expansion are the main problems of cities in the developing countries. It is necessary to recognition and analysis of land properties and it’s suitability in addition to socio-economic analysis for appropriate control of physical development and urban sprawl. The aim of this study is analysis of gully erosion phenomena and its effect on the physical development of Mohr city in the southern of Fars province. According to this, the goal this study is recognition of phenomena and geomorphological process effect on the physical development of city with an emphasize on gully erosion and its limitation. The materials used in this study consist of topographic maps (scale 1:25000), geology, land use data and aerial photos of the years 1957, 1995 and 2014. After preparing all of the data, AHP method has been used for zoning of gully hazard erosion in the study area. The result shows that physical development of Mohr city is face to the geomorphological limitation in all direction. But the processes of gully erosion and slope are the main limitations of urban development. It seems that the most of these constraints are in the north, northwest, northeast and south of Mohr city. Also, the results of gully erosion zoning show that lithology, land use, distance from the streams, slope and distance from the roads have the most value respectively in gully erosion and the Mohr City is in the high and very high zones. Engineering methods for controlling streams in short term and watershed management for controlling runoff in long term and management program for soil modification are the main approaches to preventing gully erosion increasing in Mohr city.

This study investigates hydrocarbons and heavy metals pollution in air, soils, and plants in Baghershar and its peripheral located in about 4 km south of Tehran by using an analytical descriptive method. As area study has a favorable situation near Tehran megacity and has had proper geographical conditions, many giant plants including Tehran oil refinery and its relatives and so many other pollutant plants and workshops have been located here since the 1960s. The analysis is based on sample measurements of 12 samples of air, 24 samples of soils and 24 samples of perennial plants. The finding shows that the region is polluted by hydrocarbons and heavy metals origin from the plants and their relative transportations. The high density of the contaminants in the air could be harmful to human life and so could leave harmful effects on soils and plants. High values of hydrocarbons and zinc in samples show that the soils in the region are polluted too. Although the values of nickel and vanadium were lower than the standard level, but the high levels of contaminants in the soils could be a risk for plants and water resources. Measurement of sample plants indicates that hydrocarbon and zinc contaminants had a higher density than others and the higher values obtained from Baghershar urban areas. Although the concentration of the heavy metals in plants are far from crisis level, but as the values are high, its expect them to increase in the future and cause many harmful effects. Finding also shows that pollution in the area study has being affected by the oil refinery and relative activities in storing, distributing and transporting of oil products.