فصلنامه جغرافیای طبیعی
پیاپی 29 (پاییز 1394)

The results showed that among nine weathering models in Peltier model, three models happened in the climatic conditions of gharasou basin. Northern part of the study area is savanna area. The dominant features of the savanna are Current water activity with extreme intensity to low and the average impact of prevailing winds in the region. Southern part of the study area due to high temperature and low precipitations are located in arid regions and the most important Geomorphodinamic characteristic of these areas are the effects of wind, Current water activity and weak mass movement. Also result shows in mountainous regions there is weak mechanical weathering. In north of case study due to heavy precipitations and high temperature, Chemical weathering is more moderate type. While weathering in most parts of the study area is mostly chemical.

The main objective of this study is to understand atmospheric circulation patterns, responsible for the development of drought and wet periods. For this purpose, droughts and wet periods during the 30-year period were identified in the six synoptic stations in central Iran. The base component analysis using varimax method of data correlation matrix and during the five hPa geopotential height and sea level pressure was to identify the basic elements of the atmospheric circulation. Then, using cluster analysis method on these components are bonded into circulation patterns were identified drought and wet. The main component of the study showed that more than 42% of the variance drought geopotential height at 500 hPa data by expanding the width of the lower polar low is that high elevation areas such as southern Siberia high elevation and high elevation or pressure tab on the research area is the cold air, air filter and associated cloudiness and creates stability, low rainfall and the occurrence of drought. The principal component analysis showed that the wet period of the first component Maximum percent rise a major role in the circulation patterns that indicate negative step-polar and Siberian high pressure that has two separate bovine eye model and the remaining components are due to negative steps and positive cells indicative of atmospheric instability coming from the Mediterranean and the Black Sea and the Red Sea to penetrate into the area, causing the event to be wet.

Dust is the first Natural hazard in desert and semi-desert world and Iran. In order to identify the days of the dust of South KHorasan, the daily amount of horizontal visibility, wind speed and direction in the spring and summer of 1991 -2008 were received from Meteorological Organization. Then, based on Shao and Dong index, the days were extracted with dust. In order to determine atmospheric pattern led to the dust, the daily Geopotential height 500 HP from the National Center for Environmental Prediction America/ National Center for Atmospheric Research (NCEP / NCAR), was prepared. In this study, to determine the pressure patterns were used the principle component analysis approach in the state S and hierarchical clustering (ward). Then the composite maps of vorticity, geopotential height, and sea pressure and flow pattern for each pattern produced and were analyzed. The results showed that the tow dominant synoptic patterns respectively are the summer pattern with a subtropical high on Iran and high low on Pakistan in the high levels of the atmosphere and the pressure difference between the South-East of Iran (low pressure) and the Caspian Sea (high pressure) on the land surface. In this pattern, the wind from the East of the Caspian Sea and Turkmenistan desert in the dry lands and deserts to eastern Iran flows and causing dust. This atmospheric conditions is this Connection with the 120-day winds of Sistan and Baluchestan in Iran's East. In the spring pattern, the trough of westerly winds in the center and east of Iran in the high level of atmosphere and low pressure on the ground in this area has led to unstable weather conditions in the central deserts of Iran and the West the province that these flows transfer dust particles and reduce visibility. As well as intense pressure difference between the centers lead to dust storms in the South Khorasan province.

Climate change is one of the common problems in today’s societies and considerate as threat for earth. Increasing of earth temperature is cased to extensive changes in earth climates and also it laded to same variations of spatial and temporal of precipitation so that these variations cased to a lot of damages especially in last decade. This study to identify of variations and the trend of season and duration of precipitation in different times intervals. Then it is predicted same changes in the future by the method of artificial neural network. In this study we have us of the data from two synoptic stations Hamadan and Nojeh .The statistic’s years in this study; it seems the rainfall season in the central part of Hamadan province in started later and ended later in last decade. In other words the starter of rainfall season in Hamadan which occurred in the fall season, at present tend to ward the winter season and the fall season is more dryer than before ages. This shows that the rainfall season is interchanged in this district. in using of the method of artificial neural network we should consider to two main points in the predicting of precipitation the first one, the low attention of this method in the long –term predicting of precipitation and the second one, the exaggerate in the minimum and maximum amount of precipitation in different seasons of year.

The purpose of this research is to study the method of distribution of thermal models of land surface and the normalized indicator of vegetation and the relationship between these two variables in the cold and hot seasons in Isfahan city as one of the most important population centers in Iran. In line with this objective, employing the four images of the Landsat TM sensor, the land surface temperature and the normalized Index of vegetation in a 19-year time span was made in the dates of January 7, 1991, June 16, 1991, December 29, 2010 and July 4, 2010. The results of the research showed that: On 7 January, 1991, the minimum temperature of-1/1 centigrade, the maximum temperature of 16 centigrade with an average of 5/1 and standard deviation of 1/4 were calculated. On 16 June, 1991, the minimum temperature of 16, the maximum temperature of 33 centigrade with an average of 28 centigrade and standard deviation of 3, On 4 June, 2010, the minimum temperature of 18, the maximum temperature of 37 , with an average of 29 centigrade and standard deviation of 3/2, On 29 December, 2010, the minimum temperature of -3/6, the maximum temperature of 19, with an average of 7/7 centigrade and standard deviation of 3/2 were calculated. Also, the index minimum On 7 January, 1991 of -0/96 and its maximum of 0/78 with an standard deviation of 0/1 and On 16 June, 1991, the minimum index of -0/36, the maximum of 0/66 and the standard deviation of 0/14, On 4 June, 2010, the minimum index of -0/23, the maximum of 0/68 and the standard deviation 0/11 and on 29 December, 2010, the minimum index of -0/4, the maximum of 0/56 and the standard deviation of 0/066 were calculated. The dispersion of the hot temperature range in the regions of 5, 6 and 13 and in the cold period of the year and the hot temperature range in the regions of 6 and 5 and cold in the peripheral regions of Zayandeh Rood (River) in the hot period of the year is observable.

soil erosion is one of the most important factors that a large part of the territory of the country annual threat and reduce the quality of agricultural land and destroys the same addressing the problem of soil erosion and management strategies for prevention and weakness of the negative effects it is important, Also in area where neo tectonic movements caused by tectonic activity in the area and shape responses to these impacts will occur and continue drainage area in a regional tectonic model net work waters effect drainage patterns and drainage net work and is heavily influenced this study attempts to investigate these dement delivery and activities in neo tectonics in Koor - chamriz basin its north western Fars province. The investigation method in this study was based on applicable goal and related to descriptive- analytic method and approach. The results show that the development of geological formations susceptible Vf (1/33 and 1/42) and Bs (2/02) in the drainage system and causes erosion and sedimentation in the basin. The results of morphometric data of the drainage system, geometry, with some indicators to evaluate the susceptibility to erosion groove area and empirical formulas for estimating the extent and severity of damage and sediment deposition in the region. Erosive average annual rainfall in the basin, 502/6383 ha estimated and indicated that soil erosion. 16.6average acidity of soil in the basin is for ideal for growing plant.

Drought is a climatic phenomenon caused by a period of unusual dry conditions which is stable enough to cause instability in the hydrological situation of an area. The average annual rainfall of the country is about 250 millimeters that is less than the average rainfall of Asia and about one-third of world’s average rainfall. According to Khuzestan station’s rainfalls and based on the Belter’s method, Khuzestan is located on the dry to mid-humid climatic region. Due to the importance of drought and its effect on the economic, social, biological, and even cultural issues, it is necessary to exactly assess this phenomenon. One of the significant and fundamental elements in drought studies in each area is the detection of some indexes for the intensity and lasting of drought period. In this paper, drought phenomenon in two stations of Mahshahr and Andimeshk in a period of twenty years (1370-1389), was analyzed by using the rainfall standardized index (SPI), percent ofnormality (PN), Nietzsche method, normal Z and decileindex. The results proved that in all the indexes, the years with normal rainfalls are more stable and lasting than the dry and humid years. So, based on the SPI index, Andimeshkstation has 13 years of almost normal rainfall.
During this twenty years period, a terrible drought had happened on the year 87. Mahshahrstation has 15 years of almost normal rainfalls that is 2 years more than Andimeshk. Very strong humid year only happened on the year 76 and on the year 87,and the average drought was recorded for this station. According to PN index, on the year 87 on both Andimeshk and Mahshahr stations a terrible drought happened. According to Nietzsche method, 13 normal years in Andimeshk and 15 normal years for Mahshahr had happened. According to normal Z index, 2 years on Andimeshk(1381-1387) station and 1 year on Mahshahr (1387) was attributed as a rainfall with drought. According to deciles index, the driest years in both Andimeshk and Mahshahr stations are 87 and 78 which are in the first decile.

Drought is one of the natural hazards that humans are constantly exposed. Therefore, it is necessary to recognize and analyzed. Drought indices, in fact Indicate the normal limits of droughts occurred during Time period to do possible to evaluate different spatial and temporal scales. Daily precipitation data in a 57-year period (1951-2007) were received. Data in this database is in form of cell 0/25× 0/25 degree arc to the Middle East. To convert the database to a text file (TXT) format, it converted to useable formation MatLab software by programming in Grads software. The next step is the calculation of the indices described in MatLab software. To map the output data, the Surfer and ArcGIS software were used. In this study the data output is seasonal and annual, ultimately standard rainfall index shows the drought rate and has been compared with DI index. Comparison annual maps of deciles Index and the Standardized Precipitation Index shows that the eastern part in Northwest of Iran is Wetter than the western part according to a period of 58 years and The western and central regions of Azerbaijan have drought.