فصلنامه پژوهش های جغرافیای طبیعی
پیاپی 81 (پاییز 1391)

Erosion is the process by which soil and rocks are removed from the Earth's surface by natural processes such as wind or water flow, and then transported and deposited in other locations.Human activities have dramatically increased (by 10-40 times) and accelerated the rate of erosion globally. Excessive erosion causes problems such as desertification, decreases in agricultural productivity due to land degradation, sedimentation of waterways, and ecological collapse due to loss of the nutrient rich upper soil layers. Water and wind erosion are now two primary causes of land degradation; combined, they are responsible for 84% of degraded acreage, making excessive erosion as one of the most significant global environmental problems. Water is the most important erosion agent and erodes most commonly as running water in streams. Raindrops (especially in dry environments) create splash erosion that moves away tiny particles of soil. Water affecting the surface of the soil as it moves towards tiny rivulets and streams and creates sheet erosion.In streams, water is a very powerful erosion agent. The faster water moves in streams, the larger objects it can pick up and transport. This is known as critical erosion velocity. Fine sand can be moved by streams flowing as slowly as three-quarters of a mile per hour.

Growth in our understanding of active tectonics and tectonic geomorphology during the past 25 years has made it clear that tectonic processes happen at a variety of scales relevant to human history. This fact has presented researchers with an important question that what is the impact of active dynamics of earth's crust in continental region on human societies in both our past and future. A review of published studies shows that there are two viewpoints about the relation between active tectonics and humans. Some of the researchers emphasize the dangers of active tectonics for human beings. The other group of researchers believe that tectonic is an important factor in the evolution of humans, civilization, and the formation of ancient complex cultures.

Within a synoptic weather, the classification of ambient weather conditions into categories is a useful tool for numerous climate impact applications.Air mass is a large and homogeneous volume of air which is adequately located over a certain area and captured properties of its below area. In order to form air masses, it is necessary that air remains stable in an area for a long period of time. Ultimately, general flows of air make them move. While moving and passing different regions, characteristics of air masses are changed, modified and also transformed into another air. A location’s climate follows air masses entering to that region and, reflects geographical conditions of that location. One of the objectives of synoptic climatology is to carry out synoptic categorization or to determine dominant air types (climate) in a location in a year. Air masses are generally categorized based on potential temperature and humidity. However, other criteria are considered as bases for their categorization.The Sistan basin is located in a arid zone with less than 60mm precipitation. This region in the east of Iran and northern regions of Sistan and Baluchistan Province has special climate that is affected by severe winds and dusty air.This climate distinguishes this region from others in Iran. The region depends onHirmand river and its embranchments inflows that import more than billions cubic meter waters and can support the survival of Hamoon international wetland and the populations of region.The occurrence of periodic fluctuations in water inflows and potential climatic, geomorphologic and hydrologic conditions cause the surface to be exposed in winds flows. In Sistan region winds are blown throughout the year, but during the June to September the direction, frequency and intensity of wind blows are more pronounced. This wind is distinguished as 120 days winds and is one of the most famous moderate scale wind systems in the northern hemisphere.Identifying effective air masses on this region is of considerable importance in order to better plan and make use of available resources in this region. It is because of the fact that by the analysis of its effects on the surface phenomena (e.g. dust), environmental planners would be able to find better ways for decreasing environmental problems. Finally recognizing these relationships allows us to predict many environmental accidents in order to, at least, decrease their harmful effects by these predictions.MethodologyIn this paper, to identify the prevailing air masses in the North of Sistan and Baluchestan province (East of Iran),daily data of 14 climatic variables of Zabol weather station were used.The data were considered against atmospheric variables and utilized as a P matrix from 21/03/1975 till 20/03/2005. At first, to explore the major source of variance in climatic variables in the region, a Principle Component Analysis (PCA) was applied to the Z scores of primary data in a 10825*14 cells matrix. Findings showed that three principle components (Thermal-humidity, Wind and precipitation) could account for 87 percent of data variances and were selected as the most effective factors. Then, the principle components matrix was used as input variables in a cluster analysis for identifying prevailing climatic conditions of the region. Principal Component Analysis (PCA) involves a mathematical procedure that transforms a number of (possibly) correlated variables into a (smaller) number of uncorrelated variables called principal components. The first principal component accounts for as much of the variability in the data as possible, and each succeeding component accounts for as much of the remaining variability as possible. To obtain classes from a PCA, the component scores can be grouped via cluster analysis. A common procedure involves hierarchical clustering. HCA is a technique of choice for exploring and visualizing large data sets. HCA consists in calculating the dissimilarity, usually called the distance, between the individuals with one individual corresponding generally to one column of the data matrix.

Some of phenomena have certain relationships which cannot be raised as correlation, but they considered as duality. Concept of duality is regarded when a phenomenon with another phenomenon is dual. Although each of these phenomena are independent in nature, there is a relationship between them. So, we will analyze the behavior of phenomena in relation to other phenomena.Earth subsidence has been one of the important issues jeopardizing environment and there are many studies, which blame shortage of underground water resources for having uplift and subsidence. However, many argue such conclusion and believe that earth subsidence has been studied in the past without considering the changes in the hill over a long period. In this study, we use SAR interferometry study to investigate earth subsidence in many plains of Iran and explain duality theory in the geomorphology. Concept of duality in geomorphology is mostlyrely on the land subsidence and the uplift in the adjacent hills.Mahyar plain is located 25 kilometers south of city of Isfahan, Iran. The region is covered with calcareous rocks of cretaceous and there are many rocky mountains. Many sediment erosions cover the areas of desert and there are various faults.Yazd- Ardakanregion is located in central part of Yazd and it contains many well-known faults. Ardabil plain is located in west northern part of Iran.

In arid and semi­arid areas, dust storms occur frequently. When surface winds are strong, large amounts of sand and dust can be lifted from bare, dry soils into the atmosphere and transported downwind affecting regions hundreds to thousands of kilometers away. Dust storms are most commonly caused by strong pressure gradients which cause an increase in wind velocity over a wide area. For countries in and downwind of arid regions, airborne sand and dust presents serious risks to the environment, property and human health. In recent years, systematic research on dust storms has been carried out. Dust storm in the east of Asia, is quite well documented through the analyses of synoptic records over the past 50 years (Sun et al., 2001; Zhou, 2001; Chun et al., 2001; Qian et al., 2002; Natsagdorj et al., 2003; Kurosaki and Mikami, 2003; Shao and Wang, 2003). Sun et al. (2001, 10331) analyzed the synoptic reports over the 40­years period between 1960 and 1999 and found that Gobi in Mongolia and north of China are major dust sources. In this paper, we identify the main sources of dust production, test forward trajectory technique and investigate characteristics of pressure patterns of dust events in July 2009 in Western Iran.

Air pollution is one of the major anthropogenic related productions which has had direct or indirect impact on environment during past recent century. Tehran metropolitan is one of the polluted cities in the world, in such way that in 2010, 120 days out of 365 days, were much polluted with one or several polluted elements. The major aim of this work is to map air pollution of Tehran metropolitan using new technique and method of magnetometry of tree leaves. Application of magnetic measurement is known as a new advanced method in investigation of the magnetic mineral emitted in to the air in industrial area.In recent years magnetic measurements have been increasingly used as a proxy for the heavy metal content in soils and sediments influenced by industrial emissions. Also, Magnetic particles are found almost invariably amongst atmospheric particulate pollutants. But sometimes it is difficult to judge if the measured distribution really reflects the present situation or if it is a product of past industrial activities. Therefore, we tested,to what extent, magnetic measurements of tree leaf samples can give information on the current spread of magnetic dusts. In fact, this project examines the capability of Tehran air pollution to produce some pollutant elements applying magnetic parameters leaves in urban green space. These elements deposited by vehicles and plants. Tree leaves with large surface areas can accumulate efficiently urban dust on their surfaces. This dust is partially washed out during rain precipitation, and therefore, monitoring pollution through the magnetic properties of tree leaves provides time-averaged results, which are more useful when studying regular patterns of urban pollution, than the direct measurement of air pollutants in a short period. Due to their widespread distribution, tree leaves allow for the construction of sampling grids of different scales (e.g., from streets to entire urban areas), with a high density of sampling points and with a spatial resolution which is hard to achieve with monitoring stations.

The importance of atmospheric precipitation in human life turns it into one of the most common subject of various studies. Minimal changes in the amount and intensity of precipitation would face the communities’ social and economic infrastructures to serious problems. Even though these studies have yielded very precious results but in most cases atmospheric precipitation patterns were analyzed not only at a limited regional scales but also only for heavy precipitation (high intensity precipitation). However, synoptic weather patterns, creating precipitation or other atmospheric phenomena, are formed within hemisphere-scale pattern. Among them, blocking pattern is one of the most important large scale circulations. As sometimes blockings embrace a wide range of western Atlantic coast to the Far East. Undoubtedly the identification of these patterns naturally requires a study area much wider than synoptic scope. In addition, understanding of the extreme natural phenomenon like heavy precipitation requires the knowledge of their normal modes. Therefore, this study aims at examination of hemispheric and synoptic circulations along with both heavy (high) and normal (moderate) precipitation (intensities) in Khorasan Razavi and Khorasan Shomali provinces. Investigation of relationship between precipitation amount in Khorasan Razavi and Khorasan Shomali provinces and blocking pattern is the main purpose of this study.

The Urban Heat Island (UHI) effect refers to the temperature rise of any man-made area. It is a phenomenon in which cities become warmer than the surrounding suburbs. In other words, there is a temperature difference between the cities and the area surrounding them. Generally, the UHI effect could be a result of excessive and unplanned growth of urbanization. The behavior of artificial urban texture in terms of absorption of short-wave and long-wave radiation, transpiration, releasing of anthropogenic heat, and blocking prevalent wind is significantly different from that of the rudimentary nature. Surface geometry on the other hand, decreases wind speed in urban regions which plays a great role in formation of UHI. As the energy balance inside a city alters, UHI intensity varies. This means that UHI intensity is not spatially and temporally similar in different cities. Also it must be noticed that UHI formation in a city usually has diurnal or seasonal patterns which are mostly affected by synoptic weather conditions. There are three main synoptic and local climatology parameters affecting UHI formation: air pressure systems, cloudiness, and wind speed. Under stationary high-pressure system conditions temperature differences between urban and rural areas become large. UHI intensity is largest in calm air and cloudless sky conditions and tends to disappear in cloudy and windy weather.