Physical Geography Research
Year:2012 | Volume:- | Issue:79|Papers Count:9

Introduction: Vegetation and environmental factors have close relationships; also they affect each other in the rangeland ecosystems. This study was carried out to investigate creation of plant species spatial prediction map based on environmental factors that affect plant species. Prediction of vegetation spatial distribution across the landscape based on spatial distributions of environmental variables affecting vegetation is defined as modeling of vegetation prediction. Environmental variables maps should be available or create vegetation map to be practical and useful mapping prediction of vegetation. These prediction maps are used for biodiversity conservation, ecological restoration and assessment of impacts of environmental changes on the distribution of vegetation. To increase the accuracy of analysis, researchers have to limit the number of variables in study relationships between the environmental variables and plant species. Relationship between plant species and soil characteristics, climate and topographical factors and their effects on the distribution of plant species using logistic regression were discussed in the study area.

Introduction: Drought is a natural disastrous phenomenon that occurs due to the continuous reduction of rainfall over a short or a long period of time. A deficit in precipitation (meteorological drought) can result in a recharge deficit, which in turn causes lowered groundwater heads and a deficit in groundwater discharge (Peters et al., 2003: 3023). Given the importance of water in human life, regulating the access to reliable and sustainable water resources and planning for proper consumption are considered essential in any region. There are two types of limitations resulting from natural phenomena or improper managements by human. An increase in population in the plain of Dehgolan, the agricultural nature of the region and urban / rural development has led to the reduction of the groundwater. This phenomenon is evident when the above mentioned factors emerge. The purpose of this study is to survey the ground water responses to drought in different periods of time according to characteristics of severity and duration.

Introduction Long-term high-resolution climate proxies are essential for understanding climate variability in the region, where few long-term climate records are available. Due to cyclic variations of climate, long term climatic data for understanding of its fluctuations is necessary. One of the major problems of climatic studies in Iran is unavailability of longer useful instrumental data. Trees added annually a ring to their past annual rings in moderate climate. Annual tree rings can provide important information on long-term climate fluctuations. Trees are widespread and silent witnesses of climatic changes during their long life span which record them in their growth ring width and structure. Since annual tree rings are usually distinguishable in woody species grown in cold and temperate ecosystems, they can be used to reconstruct the past climate of different regions with annual or seasonal resolution. This paper presents a reconstruction of October-May precipitation variations in Kermanshah province using Quercuse Infectoria tree rings over the last 305 (1705-2010) years.

Introduction Vegetation has a major role in dynamic and morphology of sand dunes in desert area. Vegetation affects the movement of sands and traps sands that are transported by wind. Nebka is one of the most important accumulations landforms in desert area. The type and species of vegetation can affect on the characteristic of Nebka. This research attempted to identify echo geomorphology characteristic of Tamarix and Prosopis cineraria nebkas in the west of Lut Plain in southeastern of Iran. Lut is a desert area with many especial landforms such as Yardang, Barkhan, Star dunes and other desert landforms covering 175000 sq. kilometers area.

Introduction Entropy not only quantifies the quantity of energy but also quantifies the quality of energy and this quality is the measurement of disorder in a system (Mansly and Colleages, 2008: 145). In summary entropy in the meaning of quantification, discuss the disorder between causes and results and decisions in different topics (Van, 2009: 238).Geomorphologic hazards as a threat cause a lot of damages to human societies. In this concept natural disaster is a harmful element that exists in the physical environment for human (Ayla, 2002: 408). Landslide as one of the geomorphologic hazard cause lots of destructions as direct and indirect costs and plays an important role in destructing human facilities and causes human death, forest destruction and sedimentation in watershed basins. Identifying and classifying the areas that are vulnerable in sliding and its danger has an important role in identifying environmental hazard.

Introduction: Models of observed daily weather sequences are frequently used in water engineering design, and agricultural, ecosystem or climate change simulations because observed ground-based meteorological data are often inadequate in terms of their length, completeness or spatial coverage. These statistical models are also known as ‘weather generators’ since they can fill missing data or produce indefinitely long synthetic weather series by simulating key properties of observed meteorological records (i.e., daily means, variances and co-variances, frequencies, extremes, etc.). To date, the majority of weather generators have focused on the precipitation process in recognition of the dominant control exerted by rainfall on many environmental processes, and due to the complexity of building internally consistent, multivariable models (Hutchinson, 1995). However, companion algorithms that simulate other meteorological variables are also in routine use.Rather than simulating rainfall occurrences day by day, spell-length models operate by fitting probability distributions to observed relative frequencies of wet and dry-spell lengths. This kind of model is sometimes called an ‘alternating renewal process’(Buishand, 1977; 1978; Roldan and Woolhiser, 1982), in that random numbers are generated alternately from the wet and dry spelllength distributions. That is, a new spell length (L) is generated only when a run of consecutive wet or dry days has come to an end, at which point a new spell of the opposite type is simulated.

Introduction Dust originates from arid and dry regions where high velocity winds are able to remove mostly silt-sized materials, deflating susceptible surfaces. Dust storms as the dominant phenomena in arid and semi-arid areas have the greatest impacts on air quality. One-third of the Earth’s land area is covered by dust-producing surfaces, made up of hyper-arid regions like the Sahara that covers 0.9 billion hectares, and dry lands which occupy 5.2 billion hectares (Jickells, et al., 2005). Dust consists of particles in the atmosphere that come from various sources such as soil dust lifted by wind (an Aeolian process), volcanic eruptions, and pollution. This airborne dust is considered as an aerosol and once in the atmosphere, it can produce strong local radiative forcing. Saharan dust in particular can be transported and deposited as far as the Caribbean and Amazonia, and may affect air temperatures, cause ocean cooling, and alter rainfall amounts (Middleton, Goudie, 2001). Dust storms are important parts of air pollution resources, Phenomenon that occurs in large areas of Iran in recent years. Conditions in neighboring countries. Iran is located on the arid belt. More than half of the country's land area is arid and semiarid climate.18 provinces and 82 cities have been identified as a critical focus of wind erosion.

Introduction: Physical development of cities is inevitable and a dynamic process which will change the land cover areas. Urban growth must be led by the most appropriate land use planning. Urban land cover/use maps are used for current and future land use and urban planning. Remote sensing technology and application of satellite data in mapping land cover often will reduce costs, save time, and increase accuracy and speed. There are several methods to classify land cover. If we classify the methods of supervised classification algorithms based on complexity and accuracy, they can be divided into two main methods (the average distance to the minimum, maximum likelihood, etc.) and advanced methods (neural network, fuzzy classification methods and knowledge base methods). In support of image classification, two different methods including, Fuzzy ARTMAP classifier and Multilayer perceptron neural network classifier were used. In this study, in order to produce land cover map of Isfahan city, digital image of LISS-III scanner that was acquired on 8th August 2008 were employed.