فهرست مطالب

Natural Environment Change - Volume:3 Issue:1, 2017
  • Volume:3 Issue:1, 2017
  • تاریخ انتشار: 1396/07/30
  • تعداد عناوین: 7
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  • Manuchehr Farajzadeh *, Mohammad Ahmadi Pages 1-9
    Simplifications used in regional climate models decrease the accuracy of the regional climate models. To overcome this deficiency, usually a statistical technique of MOS is used to improve the skill of gridded outputs of the Numerical Weather Prediction (NWP) models. In this paper, an experimental synoptic-climatology based method has been used to calibrate, and decrease amount of errors in GFS numerical weather prediction model. Usually, physiographic characteristics, climatic behavior and synoptic climatology of the region are not included in MOS techniques. In this regard, an experimental model for Precipitation potential using Synoptic-climatology and Physiographic characteristics (PSP) of the region has been developed for statistical downscaling of the NWP outputs over the study region under study. A Climatic and Physiographic Index for surface weather stations is defined to represent their climatic and physiographic characteristics in MOS technique. CPI covers monthly mean precipitation, temperature, monthly number of wet and dry days, and latitude and height of station. CPI index which is defined in this paper can be used as climate classification index. In this study daily gridded outputs from Global Forecast System (GFS) has been used for calibration and running the PSP experimental model. Inputs of the model are gridded meteorological parameters in 500 hpa and surface layer from GFS model. Data from more than 85 daily weather systems have been used to find synoptic climatology characteristics, and coefficients needed as input for PSP equations in the period of 2002-2007. Coefficients are computed by using regression equation between observed and computed precipitation over each station with. 85.
    Keywords: climatic, physiographic index, Iran, numerical weather prediction, precipitation forecast, synoptic climatology
  • Ahmad Nohegar, Fatemeh Norbakhsh *, Mehdi Yazdan Panah Pages 11-18
    Qomrood river is one of the rivers that located in arid and semiarid area which has a seasonal fluvial. The river is faced many changes, because of floods or natural- human factors. This study, as a geomorphologic study, tries to survey and identify geometric changes between Kocherey dam and 15-Khordad dam. The study method is a mix of library research and field studies. In library method all papers in journals and sites that related to this topic were collected. In field studies, the data were collected through direct and indirect (satellite image) observations. For this goal, TM (1989), ETM (2000) and IRS (2009) satellite images were used. Accordingly, the tree central lines belonging to different periods of study were extracted. Then these lines separated to 6 parts with emphasize on geological and geomorphologic base. In order to change detection, fitted tangent circle model was used. This research showed that the curves of the river face to decrease, while in some parts that are located on harder geological segments, or always have water, face to increase. It means in these parts all curves and meanders are more than previous. Sinus numerical coefficient in all intervals indicates approximately 1.5 that indicates the average sinus condition of the river at present intervals, and this factor has not changed in these 20 years.
    Keywords: geometric changes, geomorphology, Qomrood river
  • Sahar Abedian *, Abdolrassoul Salman Mahiny, Hadi Karbakhsh Ravori Pages 19-32
    Soil erosion can be considered as one of the most important obstacles in the way of sustainable development of agriculture and natural resources. The aim of this study is to estimate erosion and sediment yield of basin using Erosion Potential Method, in Gorganrud basin, north of Iran. The main factors in the EPM (slope average percent, erosion, rock and soil resistance, and land-use) were evaluated using a GIS software. Then, each of the parameters has been classified in different categories based on the importance. Finally, the prepared layers integrated and overlaid in EPM model, and soil erosion map are calculated. The spatial distribution of erosion intensify classes showed that 7.4% of the total basin area had tolerate erosion, 25.9% slight erosion, 27.96% moderate erosion, 10.46% strong erosion, 9.91% very strong erosion, and 18.34% destructive erosion. The highest amount of erosion occurred in the northwest to northeast regions with lithological units including loess, and alluvial deposits and agricultural use despite the fact that slope factors in these areas were less than 10%. In the central, western, and eastern parts of the basin, in spite of 15%-55% of slope, the areas depicted a slight to moderate potential of erosion. This is supposed to be due to the dense forest coverage in the region that decreases the energy of rain droplets. Results showed that about 66.7% of the study area is classified in moderate to destructive erosion intensify (Wsp >15 t ha-1 year-1). For avoiding soil erosion in this basin, soil conservation operation should be performed.
    Keywords: erosion potential method, sediment yield, soil erosion
  • Mehran Maghsoudi *, Asghar Navidfar, Ayub Mohammadi Pages 33-43
    Understanding the situation, behavior and the nature of sand dunes and also their location, transport and deposition are very important. On the other hand, the importance of sand dunes is due to the impacts that they have on water and soil resources, flora and fauna and human infrastructure. This study, looks at the development patterns of sand dunes in Mesr erg region. In the first part, data and satellite imagery were analyzed with different time intervals. In the second part, wind data of Ardestān, Isfahan, Kashan, Natanz, Khoor and Byabanak stations were studied to monitor the status of the wind regime, and its impact on the dynamics of the Mesr sand dunes. The results indicate that the area affected by the prevailing winds from Northwest Southeast direction during the cold days during the entire year, so that major translocations fit this trend in the erg surface. However, average Migration over the dunes was measured 8 meters per year. During the summer, following the establishment of a low-pressure system over the Dasht-e Kavir, winds from the Northeast direction result in irregularities in the sand dunes morphology, therefore evidence of these irregularities, is the dunes Migration to the Southwest direction.
    Keywords: Mesr Erg, sand dunes, Sand Migration, satellite imagery, wind data
  • Tayebeh Shojaee*, Gholamabbas Fallah Ghalhari Pages 45-58
    The present study aims to investigate the structure and trend of climate parameters affecting grape growth in Khorasan Razavi (north eastern Iran) in the period of 1991-2015 in 8 weather stations. Effective climate elements such as temperature, precipitation, the number of hot days, the number of frost days, sunshine hours and parameters such as maximum temperature, annualaverageannual average of temperature and precipitation, the growing season and phenological stages were calculated, and their effects on the quality of grapes were assessed. In general, Thethe results indicatedd that in general, the warming in the growing season with a significant increase in great accumulation indices, particularly the increase in the maximum temperature, mean temperature, the number of days with maximum temperature bigger than 90th percentile, and the number of days with the maximum temperature greater than 30 °C. Precipitation during the growth period particularly in the germination and blooming for all stations is reduced. This issue indicates potential soil moisture stress during this vital growth stage. Analyzing the crop evapotranspiration (ETC) indicated that because of warming, demands for water in the region have increased from 10% to 20% percent. These observations along with the continuation of global warming indicate that grape growth with favorable quality is impossible without adopting adaptations to the future climate changes.
    Keywords: climate change, grape, phenology, precipitation, temperature
  • Mohammad Saligheh, Fariba Sayadi * Pages 59-70
    Indian Ocean is known as a source of moisture for southeast of Iran due to summer precipitation. In this study, in order to investigate the role of SST of Indian Ocean, and the convergence and divergence fields in the precipitation of southeast of Iran, precipitation data of five synoptic stations were used during 2000-2010, including Iranshahr, Khash, ChahBahar, Zabul, and Saravan. To investigate synoptic circumstances of precipitation, different atmospheric levels of data was obtained from National Oceanic and Atmospheric of United States (NOAA) website with the horizontal resolution of 5.2 degree. Afterward, maps of wind, heights, and moisture flux were prepared. The results show that these three important factors (including Indian Ocean surface temperature (SST), convergence and divergence fields, and monsoon returned east jet stream) have one important role in the summer rainfall event for the study region. In addition, summer precipitation is influenced by the wet and shallow summer monsoon, sea surface temperatures, and convergence and divergence in continental regions. East jet stream have also been effective in these regions. Summer rainfall patterns. have played roles in this region, including the convergence of the wind in southeast of Iran and the divergence of wind in the southeast of Arabian Peninsula in first pattern. The above circumstances as well as high temperatures of sea surface are considered in second pattern, and high sea surface temperature and the monsoon East jet stream in third pattern.
    Keywords: convergence, divergence, geo-potential height, sea surface temperature, the upper divergence
  • Tahereh Ensafi Moghaddam*, Shirin Mohammadkhan Pages 71-80
    Water resources in arid and semi-arid regions are heavily influenced by climate change, water shortage, water regulations, and increased water demands. Monthly discharge is one of the most important factors in hydrological studies. Some of the basins are not equipped with adequate hydrometric equipment. In such a case, average monthly discharge could be estimated by regional monthly water balance models of representative basins. In this study, the following collection of data including: temperature, precipitation and average monthly discharge, and the potential evapotranspiration was calculated by Thornthwaite equations. Remaining parts of water balance equation including: Actual evapotranspiration, soil moisture supply of the area in each month and later months are also estimated via Thornthwaite model. The net water requirements were estimated using the model by assuming that evaporation is the only path for water loss. The results have indicated that timing of recharge is very important in preserving sub-basin hydrology in this region. This modified climate diagram prompts an intuitive understanding of the relationship between recharge and consequent wet spell in Mighan sub-basin of Arak. It may be used as a standard tool to determine adequate water demand in water resources management of the arid regions for wetland protection or restoration.
    Keywords: evaporation, monthly water balance, Mighan sub-basin, Thornthwaite, Water resources