فهرست مطالب

Desert - Volume:13 Issue: 2, Summer - Autumn 2008

Desert
Volume:13 Issue: 2, Summer - Autumn 2008

  • 224 صفحه،
  • تاریخ انتشار: 1388/06/20
  • تعداد عناوین: 12
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  • Khoush Akhlagh F., Ouji R., Jafar Beyglou M. Pages 89-103
    The effective patterns and mechanisms of synoptic systems during the wet and dry spells in Midwest of Iran (MWI) analyzed and discussed on seasonal scales from 1974 to 2003. Synoptic Analysis is based on synoptic charts on Sea Level Pressure (SLP), 850 and 500 Hpa levels. The results of synoptic analysis show that dry spells in MWI are mostly corresponded to Azores High (AZH) intensifying and its central movement to east and northeast of normal position. Furthermore the Siberian High (SH) ridge is extended from northeast to Iran. The linkage between SH and AZH ridges through Iran, Mesopotamia (Iraq) and Arabic Peninsula lead to drought occurrence in the Middle East especially Iran. The Sudan Low (SL) and Mediterranean Trough (MT) have a limited extend during drought periods (dry spells). The most important occurrence index of droughts in upper charts is reinforcing and extending northward of Arabia South High (ASH) to Iran and Mesopotamia. This event is marked by a strong ridge in 500 Hpa charts over study area. The Circumpolar Vortex (CPV) is contracted to polar area during dry spells and expanded equatorward in wet spells. In Summarized SH extends during wet spells but dose not reach to Iran. In addition Mediterranean East Trough (MET) reinforced and extended from 25°E to 40°E and its meridional expands reaches to the Red Sea (RS) and Sudan Low. The other result is that during wet and dry spells, the orientation of Blocking Highs ridges in the north of Caspian Sea and over Ural Mountain (UM) causes different climatic conditions in Iran.
    Keywords: Synoptic climatology, Wet spell, Dry spells, Atmospheric action centers, Midwest of Iran
  • Shamsipour A.A., Alavi Panah S.K., Mohammadi H., Azizi G., Khoush Akhlagh F Pages 105-115
    Drought is a major problematic phenomenon for the mostly semi-arid country of Iran. The north central regions of Iran (north of Esfahan and Ghom province) have suffered from severe droughts several times during the last three decades. The frequent occurrence of drought in these regions is due to low and inconsistent precipitation, abnormally high temperatures, increases in surface albedo and evapotranspiration; especially during spring. The surface characteristics of Kashan and Ghom regions consist of salty flats and sandy hills covered by sparse vegetation. The average elevation of the area is 1987 mASL. In the present work, NOAAAVHRR data have been employed to assess vegetation indices and environmental conditions in the study region for the years 1998 – 2004; which are then compared to actual ground data such as rainfall, temperature and relative humidity for a detailed drought analysis. Spatial and temporal variations of meteorological droughts in Kashan have been analyzed using Standardized Precipitation Index (SPI) at annual and seasonal scales, and have been generated through GIS based interpolation. Vegetative and thermal drought indices have been calculated using NDVI, VCI, and TCI values derived from NOAA-AVHRR data. Results from applying remotely sensed data show that this area is generally of low vegetation index values. The artificial forests and farmlands at the foothills of the mountains northwest of Kashan region showed relatively high vegetation index values. TCI and VCI generally show a good relationship with meteorological observations. According to the output of utilization NDVI and VCI, 2000 and 2001 years were characteristic of drought conditions, while 20 and 2004 did non represent drought years. Since TCI index is completely dependent on surface temperature, the combined analysis of the May and April results were influenced by the low land surface temperatures experienced in April, and therefore it was very different from the other indices i.e. NDVI and VCI. Therefore thermal IR channels can be employed used to monitor drought conditions in the semi-arid and arid regions of Iran to assess these regions, environmental conditions.
    Keywords: Drought Indices, Remotely Sensed Data, AVHRR, NOAA, NDVI, Central plains of Iran
  • Esmaeili A., Ahmadi H., Feyznia S., Ghodousi J. Pages 117-127
    Soil erosion results from an interaction of several parameters, which vary in space and time. Awareness of environmental changes and their impact on the intensity and spatial pattern of water erosion can effectively help in recognition of erosional reactions versus the affecting factors. The aim of this paper is to describe the development of a methodology based on present knowledge and available data, for evaluation of water erosion behavior and risk as well as an estimation of soil erosion. Accordingly, based on the conducted research on different types of water erosion in some areas of Baleghli Chay Watershed, between two hydrometric gauging stations were studied, with an exclusion of erosion due to mass movements. Four major types of water erosion namely: sheet, rill, channel and streambank which play a considerable role in sediment yields of the area, were separately studied. In order to determine the inter-effects of erosive factors, the study was conducted using multivariate statistical tests. For each erosion type, an individual model was then presented. The results indicated complex and different interactions between the likelihood of water erosion and environmental changes in the study area. Sheet and rill erosions act differently from channel erosion while streambank erosion is completely different from others. Therefore, a study of individual types of water erosion can help in recognition of accelerating factors that effectively influence water erosion, and consequently to come up with appropriate models.
    Keywords: Water erosion, Erosion model, watershed, Baleghli Chay, Ardebil, Iran
  • Moeinrad H Pages 129-136
    To determine the relative salt tolerance and/or resistance in seedlings of pistachio genotypes, four pot experiments were conducted. In experiments 1 and 2, the effects of salinity on growth indices were studid. Experiments were done in the form of split plot based on RCBD. In each experiment, mainplots consisted of different electrical conductivities of irrigation water (ECiws). In experiment 1, the seedlings of seven cultivars (cvs.) of Pistacia vera L. (Momtaz, Akbari, Kale-ghoochi, Owhadi, Ahmad-aghai, Sarakhs, Badami-riz) and also P. atlantica sub. Mutica (Baneh) were allocated in subplots. In the second experiment, three cvs. of P. vera L. (Badami riz,Momtaz and Owhadi) with different salt tolerances were used. In order to determine the resistance of pistachio cvs. in respect to seedlings survival, experiment 3 was done. In experiment 3, salinity treatments continued upto 70% of leaf damaging in seedlings. In experiment 4, the effects of salinity on pistachio seedlings in regards to chlorophyll-meter figures and proline contents studied. Nevertheless, the ratio of damaged leaves, K/Na ratio and total dry weight was determined. In experiment 4, the relationship between some physiological traits and salt tolerance in pistachio genotypes determined. We observed that not only salt tolerance varies cv. to cv., but also it changes in different sources of a given cv. In order to determine the salt tolerance of pistachio genotypes, the sensible traits (relative percent of total dry weight and seedlings survival) were more reliable than traits such as K/Na ratio, chlorophyll meter figure, and/or a single physiological character as same as leaf proline content.
    Keywords: Chlorophyll meter figure, Growth indices, Pistachio, Proline content, Salt tolera Seedlings survivalnce, resistance
  • Fatahi E., Nouhi K. Pages 137-146
    Frost is one of the atmospheric phenomena which seriously threaten crop production. It also causes numerous accidents in mountainous roads. In this research the Spatial Synoptic Classification SSC method was employed to classify the type of air masses. For the classification, such meteorological data as: temperature, dew point, mean sea level pressure, cloudiness, direction and speed of wind were collected for a period of 45 years from 1961 to 2005. For a classification of air masses a discernment method was applied and while typical characteristics of seed days being used as input for this discernment function method. The results indicated that, spring season air masses, Dry Polar (DP) air masses, Moist Polar (MP) and Moist Moderate (MM) air masses have contributed most to the occurrence of advection frosts respectively. Dry Polar air masses bore the lowest temperature and dew point, along with northerly and easterly wind components and a clear sky. These air masses caused the occurrence of the most severe and most extensive advection frosts in south west basins of Iran.
    Keywords: Air masses, Spatial Synoptic Classification SSC, Principal Component Analysis (PCA), Frosts, Iran
  • Shamekhi T., Mohammadi Kangarani H., Blanchez J.L Pages 147-154
    Desertification of the arid and semi-arid lands of the world has been proceeding for more than a thousand years. Human-induced degradation in these areas is regularly cited as one of the principal causes of desertification. Euphrates and Tigris Basin as the case study of this research in some aspects is almost unique in the world. But this basin has been confronted to progressive desertification. This research was done for proposing appropriate policies in terms of main driving forces in order to combat desertification in this basin. So qualitative analyses of data banks of the countries involved in this basin have been collected by FAO consultants, showed desertification in Euphrates and Tigris Basin is characterized by climate factors and human activities; water scarcity and unequal distribution of water are major climate factors. The main human activities are overgrazing of rangelands, deforestation, and land use changes. Because of negative impacts of human activities on climate factors and also deep dependency of livelihood in this basin, there is an urgent need to plan an integrated watershed management in order to managing people, water, forests, and range lands together for combating this progressive desertification.
    Keywords: Desertification, Proposed Policies, Integrated watershed management, Institutional framework, Human activities, Climate factors
  • Motaghian H., Mohammadi J., Karimi A Pages 155-165
    Soil hydrau-physical data are important for many hydrological modelings. They are the main variables controlling the key processes such as water and chemicals movement and transport in the soil profiles. This study was conducted in order to analyze the spatial distribution of selected soil hydrau-physcial characteristics including infiltration rate (IR), saturated hydraulic conductivity (Ks), bulk density (BD), clay, silt, and sand content. The study area was sampled on a pseudo-regular sampling scheme with initial grid spacing of 1 km during June and July 2007. Maximum coefficient of variation (CV) was found for IR (72%) and Ks (67%). While, BD showed a minimum CV of 9%. Statistical analyses illustrated that there is a significant difference (P<0.05) in the mean values of IR in two different landforms, i.e., plateaus and alluvial plains. However, different land uses including rangelands and dry farming revealed no significant differences in the mean values of measured IR. The contrasting results were obtained for Ks. Geostatistical analyses revealed that the spatially dependent stochastic component (structure) was predominant over the nugget variance (noise). The developed and modeled variograms of each variable were used in generating kriged maps. As expected, these maps exploited spatial similarities among soil properties.
    Keywords: infiltration rate, Kriging, Saturated hydraulic conductivity, Variogram
  • Azimzadeh H.R., Ekhtesasi M.R., Refahi H.Gh, Rouhipour H., Gorji M Pages 167-174
    Wind erosion is a significant problem on 20 million ha of Iran, especially in central plains and coastal areas. Wind erosion samplers, meteorological equipments and measurement procedure have been developed over the last two centuries to measure the particles moving across the field in modes of creep, saltation and suspension. In recent research as the first technical measurement in Iran, wind erosion was measured with these advanced procedures. Field data was collected from a small (1.9 ha), square, fallow field with nonerodible boundaries. Wind erosion measurement equipment containing 14 clusters with samplers at 0.05, 0.10, 0.25, and 0.50 and 1.0m above the soil surface and a 4× surface creep sampler (0 to 0.02m height by 0.005m wide) was arranged in a circular pattern. The sampling cluster consisted of an array of five samplers each attached to a pivoting wind vane and each mounted at a different height on a central pole. This permitted field erosion data collection regardless of the wind direction and provided a range of field lengths with a minimum number of sampler locations. A combination equation of power and exponential functions expressed the variation of transition material to a height of 2m. An exponential model described the horizontal distribution of transported soil in the field. Twelve single events were recorded and analyzed between May 2006 and May 2007. Several inherent soil properties such as soil texture, organic matter and calcium carbonate content affect the erodibility of soil and change very slowly in research time. Other properties, such as surface roughness and aggregate crust strength are temporal and change rapidly in response to climatic conditions. Total soil mass transported across the fallow field was measured at 220.93 kg/m per year and soil loss at 1.356 kg/m2 (13.56 ton/ha) per year.
    Keywords: BSNE, Iran, measurement, Near Surface Sampler, Wind erosion
  • Baghestani Meybodi N., Jankjou Borzelabad M., Taghi Zare M Pages 175-179
    One of the key factors in managing a rangeland is to determine the relative preference of its major plant species by the grazing livestock. Preference value of each plant species is affected by plant type, companion plants, availability by animals, phenological stage, climate condition, and the livestock species. We investigated the grazing behaviour of a native goat (Garizi) in the steppe rangelands of Iran, from May to November 2004. The study was conducted within or outside of an enclosure, representing a Good Condition (GC) or a Poor Condition (PC) rangeland, respectively. Flocks of six goats were selected randomly and their grazing behaviour was monitored by chronometers. Grazing preference was considered as the time goats had spent for grazing each plant species. The grazing season was divided into 4 grazing periods, 45 days each. Data recording in the GC and PC sites was repeated 3 times during each grazing period. The experiment was designed as the completely randomized blocks. In the GC site, grazing pressure on the perennial grass Stipa barbata and the perennial chenopod Salsola rigida was low at the beginning of the grazing period, but it was increased towards the end of the grazing season. In the PC site, the main grazing pressure was on noxious plants such as Scariola orientalis, Launaea acanthoides, and Cousinia deserti. For both GC and PC sites, the time of grazing had significant influences on relative abundances of annual plants and plant litter, which subsequently changed diet selection by the Garizi goat.
    Keywords: Preference value, Arid rangelands, Garizi goat, Yazd, Iran
  • Kalteh A.M., Hjorth P Pages 181-191
    Over the last decade or so, artificial neural networks (ANNs) have become one of the most promising tools for modelling hydrological processes such as rainfall runoff processes. However, the employment of a single model does not seem to be an appropriate approach for modelling such a complex, nonlinear, and discontinuous process that varies in space and time. For this reason, this study aims at decomposing the process into different clusters based on self-organizing map (SOM) ANN approach, and thereafter modelling different clusters into outputs using separate feed-forward multilayer perceptron (MLP) and supervised self-organizing map (SSOM)ANN models. Specifically, three different SOM models have been employed in order to cluster the input patterns into two, three, and four clusters respectively so that each cluster in each model corresponds to certain physics of the process under investigation and thereafter modelling of the input patterns in each cluster into corresponding outputs using feedforward MLP and SSOM ANN models. The employed models were developed on two different watersheds, Iranian and Canadian. It was found that although the idea of decomposition based on SOM is highly persuasive, our results indicate that there is a need for more principled procedure in order to decompose the process. Moreover, according to the modelling results the SSOM can be considered as an alternative approach to the feed forward MLP.
    Keywords: Artificial neural networks, Forecasting, Monthly, Rainfall, Runoff, runoff, Self, organizing Map
  • Keshtkar A.R., Keshtkar H.R Pages 193-202
    Land degradation is a major danger which restricting different areas of Iran. Systematic description of the environment for detection of environmental changes and the human-related causes and responses is essential in land cover change study. Use of land cover data allow detection of where certain changes occur, what type of change, as well as how the land is changing. Existing systems for classification of land cover is limited in the storage of the number of classes and is often internally inconsistent. Therefore, Food and Agriculture Organization of the United Nations (FAO), developed the land cover classification system (LCCS), a comprehensive parametric classification based upon systematic description of classes using a set of independent quantifiable diagnostic criteria. With this approach land cover change detection becomes possible at the level of conversion of a class, whereas modification within a certain class type becomes immediately identifiable by a difference in classifier, or through the use of additional classifiers as is shown in a series of examples illustrating the application of the approach to primarily vegetated areas. Our study showed this approach is match with exist information and dates for land cover mapping in Iran.
    Keywords: Boolean formula, Classifier, Degradation, LCCS method, environment
  • Dastorani M.T., Hakimzadeh M.A., Kalantari S Pages 203-210
    During past decades, increased wastewater production by human activities intensified the problem of wastewater use without causing undesirable impacts on the environment and human life. However, practice of wastewater use in irrigation crops and green spaces needs careful control because of the potential presence of unwanted constituents such as heavy metals and organic contaminants. This research was designed to evaluate the effects of industrial wastewater on soil properties in Yazd, Iran. For this purpose, two plots were prepared and irrigated for five years, one with industrial wastewater and the other with local groundwater. Finally, soil samples collected from both plots were analyzed in laboratory and important factors and elements including EC, pH, SAR, K, N, P, Ca, Pb, Fe, Cd, CaCO3 and OC (organic carbon) which are important in soil degradation and land desertification were determined. According to the results obtained from this research it should be reported that this type of wastewater may cause soil degradation due to increasingSAR, EC, pH and Pb and also decreasing N, K and OC. It is clear that soil degradation is the main factor which causes and accelerates the process of desertification.
    Keywords: Industrial Wastewater, Irrigation, Water Reuse, Land desertification, Soil degradation