per
دانشگاه تهران
پژوهش های جغرافیای طبیعی
2008-630X
2423-7760
2014-12-22
46
4
407
417
10.22059/jphgr.2014.52993
52993
Full length article
مدلسازی توزیع مکانی بارشهای رعد و برقی مناطق کوهستانی شمالغرب ایران، سالهای 2010 تا 2012
Modeling Spatial Distribution of Thunderstorm Rainfalls
Mountainous Areas of the Northwest of Iran
علی اکبر رسولی
rasouli@tabrizu.ac.ir
1
سحر نصیری قلعه بین
s.nasiri66@gmail.com
2
خلیل ولیزاده کامران
3
استاد گروه جغرافیای طبیعی دانشگاه تبریز
دانشجوی دکتری اقلیمشناسی سینوپتیک، دانشگاه محقق اردبیلی
استادیار گروه جغرافیای طبیعی دانشگاه تبریز
بارشهای رعدوبرقی از پدیدههای آبوهوایی مهم در منطقة شمالغرب ایران محسوب میشود که از تنوع زمانی و مکانی ویژهای برخوردار است، چرا که این نوع بارشها نقش بسیار مهمی در آبوهوای منطقة مورد مطالعه بازی میکند. هدف از این پژوهش بررسی توزیع مکانی بارشهای رعدوبرقی مناطق کوهستانی شمالغرب کشور به منظور مدلسازی بارشهای مکانی مورد بحث در محدودة فلات کوهستانی شمالغرب کشور است. دادههای متنوعی از جمله بارش رادار TRMM و مدل ارتفاعی منطقه استفاده و در محیط نرمافزارهای GIS، IDRISI و ArcGIS تحلیل شد. همچنین، از فناوری GIS به منظور اخذ ویراستاری دادهها، تحلیل، مدلسازی و کارتوگرافی مدلهای مکانی استفاده شده است. در نهایت در نرمافزار IDRISI مدلسازی و تهیة مدل رگرسیون دادهها انجام شد. نتایج تحقیق نشان داد که بارش رادار TRMM، با مدل ارتفاعی منطقه به میزان 63/0 همبستگی مثبتی نشان داد؛ یعنی، در منطقة مورد مطالعه با افزایش ارتفاع، میزان بارش 63/0 افزایش یافت. همچنین، این بارشها در بهار و تابستان از شدت زیادی برخوردار است.
Extended AbstractThunderstorm rainfall is one of the most important climatic phenomena in the northwest of Iran that has specific variability in spatial distribution. These rains have an important role in case study area climates. The purpose of this study is investigation of spatial distribution of Thunderstorm rainfall of Mountainous Areas of the Northwest of Iran to modeling Thunderstorm in northwest. Because of that TRMM images precipitation data from 2009 to 2012 is selected & in the software Arc Gis ,ENVI and EDRISI, have been processed.IntroductionPrecipitation is one of the crucial elements of climate that Temporal and spatial variation can control a variety of geographical area. In this case thunderstorm is one of the most important climatic phenomena of area. Sometimes these rains provide waters to crops & especially in summer leave catastrophic effects on the natural environmental and agricultural economy. Thunderstorm is related to the warm months of the year. In some cases thunderstorm rainfall can cause flooding and destructive disaster in all over the area. Therefore, this type of precipitation can be considered as a representative of regional climate, especially in spring and summer).Identification of geographic factors including elevation with precipitation of the study area and access to the regression model, the aim of this paper.Conrad (1996) in a study had shown high correlation between height and distance from the source of heat, humidity, Cold and warm precipitation in Blorych Mountainous of America. Johansson (2003) in a study about the effect of topography on precipitation distribution on Sweden slopes concluded that, precipitation increases with increasing elevation in windward slopes.Case stydy areaThe study area is located in the range of 40 to 36 degrees north latitude and 49-40 degrees east longitude, Sahand Mountainou and Arasbaran ,sabalan Bozghoush, misho, and Zagros Mountainous in West of Lake Urmia are the most important features in case study area. . Urmia Plain, moghan, plains of Tabriz, Ardabil, Sarab, Ahar are the most regions of the Northwest of iran( Motalab faed ,1386). Overall, the area climate is affected by two major factors, such as the topographic features, synoptic. The first and most important factor that affected the climatic zone, climate system in Synoptic-scale that has main role in Explanation of region climate in long-term (Masuodian , 2003).Materials and MethodsTo modeling thunderstorm rainfall, TRMM images of precipitation days from 2010 to 2012, has been downloaded from the site http://lake.nascom.nasa.gov/tovas/Interpolation This method is mainly a mathematical method that is based on the distance between points of observation that interpolated. The method of inverse distance weighting approach which is an advanced proximity of neighboring stations to estimate of the weight issue uses. in This way nearest station has more weight than the other stations.Elevation modelDEM is a simply statistical representation of the continuous ground By the large number of selected points with coordinates x, y and z of a range of optional coordinates. In the other words, DEM is a digital or numerical display of the true groundResults and DiscussionStudy of Rainfall Fluctuations to height and determine the regional gradient rainfalls relation to estimate the amount of rainfall points , Due to high levels, especially in areas without weather station is important .this is usually done as parametric methods in whether studies ( Jahanbakhsh s.2011). Regression modelThe image height as the independent variable and the dependent variable was selected asTRMM images rainfall. The Average rainfall of TRMM images from 2010 to 2012 is used as the dependent variable. R= 0/63The correlation confident above 63/0, which shows a positive correlation, Because of more than 5/0, it has a good correlation& shows high positive correlation .It means that it increased with increasing altitude, Residual sum of squares is smaller than the, Regression sum of squares .This indicates that the model has high explanatory power . The Model 99/0 is significant .T-test of the model is more than 33/2 ,as a result, T-test of model at 99/0 is meaningful.In this study has shown a high correlation between trmm rain & dem & thunderstorm rainfall is raining in spring & summer too.Keyword: thunderstorm rainfall, Modeling, spatial distribution, Mountainous Areas of the Northwest of Iran.
https://jphgr.ut.ac.ir/article_52993_4a2b880b04467b87c778df73850dec42.pdf
بارشهای رعدوبرقی
توزیع مکانی
مدلسازی
مناطق کوهستانی شمالغرب کشور
Keyword: thunderstorm rainfall
modeling
Spatial Distribution
Mountainous Areas of the Northwest of Iran
per
دانشگاه تهران
پژوهش های جغرافیای طبیعی
2008-630X
2423-7760
2014-12-22
46
4
419
434
10.22059/jphgr.2014.52994
52994
Full length article
ارتباط پوشش گیاهی با دما و آلبدوی سطحی در دورة گرم سال با استفاده از دادههای مودیس در شمال ایران
Relating Vegetation Cover with Land Surface Temperature and Surface Albedo in Warm Period of Year Using MODIS Imagery in North of Iran
حامد ادب
adabgeo@gmail.com
1
ابولقاسم امیراحمدی
amirahmadi1388@gmail.co
2
آزاده عتباتی
az.atabati80@gmail.co
3
استادیار گروه جغرافیای طبیعی، دانشکدة جغرافیا و علوم محیطی، دانشگاه حکیم سبزواری
دانشیار گروه جغرافیای طبیعی، دانشکدة جغرافیا و علوم محیطی، دانشگاه حکیم سبزواری
دانشجوی دکتری گروه بیولوژی دریا، دانشکدة علوم دریایی، دانشگاه علوم و فنون دریایی خرمشهر
پوشش گیاهی عامل عمدة نقلوانتقال انرژی بین زیستکره و جو محسوب میشود که آثار متفاوتی بر عناصر هواشناختی مناطق پیرامون خود دارد. در این مطالعه ارتباط بین مقادیر شاخص گیاهی تفاضلی نرمالشده با دمای سطحی و آلبدوی سطحی در نواحی شمالی ایران با استفاده از روشهای آمار کلاسیک رگرسیون و زمین آماری کوکریجینگ بررسی شد. سه معیار آماری میانگین قدر مطلق خطا، انحراف جذر میانگین مربعات و متوسط درصد خطای مطلق نشاندهندة توانمندی به مراتب بهتر روش زمین آمار کوکریجینگ نسبت به رگرسیون کلاسیک در برآورد دمای سطحی و آلبدوی سطحی است. نتایج تحقیق در دورة مورد مطالعه نشان میدهد که دمای سطحی و آلبدوی سطحی تحت تأثیر مقادیر پوشش گیاهی است. سپس، از روابط بهدستآمده در تعیین میزان خشکی مناطق استفاده شد. نواحی ساحلی و جنگلی دامنههای شمالی البرز با بیشترین مقدار سبزینگی (85/0) از حداقل درجة حرارت (23 درجة سلسیوس) و آلبدوی سطحی (7 درصد) مشخص است. همچنین، نواحی جنوبی رشتهکوه البرز و قسمتی از مناطق ایران مرکزی با کمترین مقدار سبزینگی (09/0-) از حداکثر درجة حرارت به مقدار 45 درجة سلسیوس و بیشترین مقدار آلبدوی سطحی (38 درصد) مشخص است.
Extended Abstract
Introduction
The most important indicator of climate in a region is vegetation community. Climate can be different over large areas, because of changes in vegetation community. Vegetation influences weather and climate in its surrounding areas mostly by way of evapotranspiration and albedo so they play a role in the earth’s energy balance. These effects on the earth’s energy balance are taken through air temperature, relative humidity, rainfall, solar radiation and cloud cover on their own micro-weather (Neilson, 1986, Small and Kurc, 2003 and Weiss, et al 2004). Disasters such as drought, flood, forest fire and among them can occur whenever the global energy balance become outside of normal range.
Remote sensing data provide valuable information for vegetation studies because it presents a quick look evaluation of the vegetation conditions. Normalized Difference Vegetation Index (NDVI), Land Surface Temperature (LST) and land surface albedo are key biophysical variables for studying land surface processes and surface-atmosphere interactions. These variabels can be calculated by transforming raw satellite data. The aim of this paper was to study relationship between NDVI, LST and land surface albedo due to the impact of vegetation on surface temperature and albedo and identify dryness status in the northern Iran.
Methodology
Study area is located in the northern part of Iran which covers with dense vegetation such as Hyrcanian forests in the north and sparse vegetation in the southern part of the Alborz Mountain range. This area is an alteration bio-climate region lying between the humid climate in the north and arid and semi-arid climate in the south.
The methodology used in this study consisted of remotely sensed data processes. The remotely sensed data processes involved data acquisition of Moderate Resolution Imaging Spectroradiometer (MODIS), data pre-processing (i.e. atmospheric correction, geometric correction, and data masking), and data processing (i.e. derivation of vegetation, biophysical indices such as NDVI, LST and land surface albedo variables). In this study, MODIS data was selected because the MODIS sensor has several benefits compared to other instruments for example MODIS has a wide swath of 2330 km that covered the entire study area. The MODIS dataset had a variety of products that each contained different levels of data processing. In this study, Level 1B dated July, 2010 (MOD021KM and MYD021KM calibrated and geolocated) was used to derive NDVI and surface albedo, and retrieving LST. This level 1B collection contains calibrated and geolocated radiances at-aperture for all 36 MODIS spectral bands at 1km resolution. In this study, Simplified Model for Atmospheric Correction (SMAC) was used for atmospheric correction of MODIS data.
Absorbtion in visible light (solar radiation) occurs in live green vegetation because of photosynthesis. Scattering (reflectance) of solar energy in the near infrared occurs at the same time. This difference in absorption and reflectance lead us to NDVI. NDVI is an vegitation index which measures this difference to show vegetation density and condition. NDVI value ranges between -1 and +1. The values close to zero means no green vegetation and close to +1 (0.8 - 0.9) represents the highest density of green vegetation. LST is an important parameter in determining the earth radiation budget and heat and moisture flow between the surface and the atmosphere and temperature strongly influence vegetation processes. Thermal bands of MODIS data (band 31 and 32) converted to radiance then converted to brightness temperature using plank law for calculating surface temperature. Albedo is also an important bio-physical indicator of reflecting land surface energy distribution and balance. In the process of broadband albedo retrieval, an empirical regression was used for MODIS data (Liang et al., 2002). Finally, regression and geostatistical approach (e.g. CoKriging) was used in this study to estimate LST and surface albedo using NDVI of MODIS data.
Results and discussion
In this study three criteria such as mean absolute error, root mean square error and mean absolute percentage error have been used to measure the differences between the values estimated for LST and Albedo using regression and CoKriging geostatistical method. The results obtained in this research indicate that the geostatistical method of cokriging has good potential to estimate LST and surface albedo using normalized difference vegetation index. The results of the study show that changes in vegetation cover alter the LST and surface albedo, leading to a local temperature change. Plants and forest have a very low albedo and absorb a large amount of energy. The relationship between normalized difference vegetation index and LST and surface albedo equations were then used to found the surface dryness condition in the study area. The result of 3D feature space of Albedo-NDVI-LST spectral shows that it has a suitable index for extracting drought information. The study revealed that coastal and forested northern slopes of the Alborz Mountain are identified with high normalized difference vegetation value (0/85), minimum surface temperature (23° C) and albedo (7%). The southern part of Alborz Mountain and the central Iran experiences low normalized difference vegetation value (-0/09), high surface temperature of 45 ° C and high surface albedo (38%).
Conclusion
In this study, the relationship between NDVI and LST and surface albedo was analyzed to estimate LST and surface albedo derived by regression and CoKriging methods. It has been recognized that there is a strong correlation between albedo, LST and NDVI. By comparison of the regression relationship among LST, Albedo and NDVI, results exhibit that LST and Albedo are negative correlations with NDVI. In this paper, a 3D feature space of Albedo-NDVI-LST spectral is analyzed for monitoring surface dryness condition. The result represents that surface albedo nad LST is affected by the change of vegetation. This 3D feature space is reliable index to show surface dryness status for soil and plant cover. it is recommended that 3D feature space of Albedo-NDVI-LST spectral can monitor to the surface dryness condition and also it is easy to operate for quick surface dryness assessment. Studies are underway to incorporate other variables in surface dryness condition.
https://jphgr.ut.ac.ir/article_52994_0cbed48c2e76d0705fa91e016581f832.pdf
آلبدوی سطحی
پوشش گیاهی
دمای سطح زمین
رگرسیون
زمین آمار
Vegetation Covers
Albedo
Land surface temperature
Regression
Geostatistical Method
per
دانشگاه تهران
پژوهش های جغرافیای طبیعی
2008-630X
2423-7760
2014-12-22
46
4
435
444
10.22059/jphgr.2014.52995
52995
Full length article
تحلیل تغییرات ناهنجاریها و چرخههای آب قابل بارش جوّ ایران
Analysis of anomalies and perceptible water cycles in Iran atmosphere
حسین عساکره
asakereh@znu.ac.ir
1
مهدی دوستکامیان
s.mehdi67@gmail.com
2
هوشنگ قائمی
asakereh@znu.ac.ir
3
دانشیار اقلیمشناسی دانشگاه زنجان، زنجان، ایران
دانشجوی دکتری تغییرات آبوهوایی دانشگاه زنجان، زنجان، ایران
استاد هواشناسی وابسته به پژوهشکدة هواشناسی ایران، ایران
هدف از این مطالعه بررسی ناهنجاریها و چرخههای آب قابل بارش جوّ ایران زمین است. بدین منظور دادههای فشار و نم ویژه طی دورة 1950-2010 از پایگاه دادههای NCEP/NCAR وابسته به سازمان ملی جوّ و اقیانوسشناسی ایالات متحده استخراج و تجزیهوتحلیل شد. برای انجام محاسبات از امکانات برنامهنویسی در محیط نرمافزار Grads و Matlab و نیز برای انجام عملیات ترسیمی از نرمافزار Surfer بهره گرفته شد. نتایج بررسی ناهنجاریهای آب قابل بارش جوّ ایران نشان داد که نواحی سواحل به دلیل همجواری با منابع عظیم رطوبتی خلیجفارس، دریای عمان و دریای خزر دارای ناهنجاریهای مثبت و نواحی مرکزی، نواحی مرتفع و شمالغرب و شمالشرق کشور به دلیل دور بودن از منابع رطوبتی و متأثر بودن از ارتفاعات دارای ناهنجاریهای منفی است. نتایج حاصل از تحلیل چرخهها نشان میدهد که چرخههای کوتاهمدت دو تا پنج ساله بیشترین حاکمیت را در کشور داشتند. با وجود این، بیشترین چرخههای کوتاهمدت در نواحی جنوبشرق رخ داده است. بیشتر دانشمندان چرخههای دو و سه ساله را با النینو – نوسانات جنوبی و گردش عمومی جوّ و جریانات مداری مرتبط میدانند. همچنین، چرخههای دو تا پنجساله را به رخداد النینو مربوط دانستند.
Extended AbstractIntroductionWater vapor is considered to be one of more significant atmospheric constituents as it contributes in precipitation and is also a critical element of the climate system. This climate element extended from earth surface to upper level of troposphere that potentially precipitable. Accordingly it called perceptible water. Therefore The total atmospheric water vapor contained in a vertical column of unit cross-sectional area extending between any two specified levels, commonly expressed in terms of the height to which that water substance would stand if completely condensed and collected in a vessel of the same unit cross section. The total perceptible water is that contained in a column of unit cross section extending all of the way from the earth's surface to the “top” of the atmosphere.The water vapor component of air requires monitoring because of its importance to weather and climate and the essential role it plays in the operation of the global water cycle. This is the reason that atmospheric perceptible water determines the potential value of precipitation as well as an index for forecast precipitation for a certain time of year. So it is an important variable in climatic study and climate change survey. Precise calculation of perceptible water needs to know about the atmospheric water vapor amount. However the amount of water vapor is determined by many factors including atmospheric density, temperature, cloudiness, wind direction and velocity, humidity in top of geographical situation. All of these factors determine the capacity of humidity, distances from the water bodies as well as leading the water vapor to any location. In this paper it has attempted to calculate perceptible water in atmospheric column from the earth's surface to the top of troposphere. This purposeful effort has been done to achieve the long term trends of precipitable water over Iran atmosphere. In order to accede this purpose the NCEP/NCAR data has been applied.Data and MethodsConsider a column of liquid water with cross-sectional area, and certain height. This height is the perceptible water. One way to determining the mass of water vapor (in grams) in a vertical column one square centimeter in cross-sectional area that extends from Earth's surface to the upper reaches of the atmosphere. Mathematically, if x(p) is the specific humidity at the pressure level, p, then the perceptible water vapor, PW, contained in a layer bounded by pressures p1 and p2 is given by Where g refers to gravity acceleration.For the purposes of our study, the pressure and specific humidity of NCEP/NCAR which exist for each 6 hours has been used. This data characterized by 2.5 longitude*2.5 latitude degree resolution. In order to find out what we had decided to find, many software including Grads, Surfer and Matlab have been used. So at first general characters including mean and coefficient of variation of percipitable water has been mapped. Then the trends maps have been represented. In addition we have used sequential Man-Kendal method to diagnosing trends during the time sequence.To find the cause and the result of this trends, humidity advection and long term change in temperature as well as precipitation over Iran has calculated. DiscussionThe mean of precipitable water in Iran is about 14.3 mm. According to coefficient of variation, the most stationary amount of the mean is at 18:00 o’clock meanwhile the most non stationary take place at 06:00 o’clock. Central Iran which located in dry region as well as far from water bodies, it contains much more precipitable water in compare to Zagros mountain chain. The most precipitable water as well as lowest coefficient of variation is happened in Caspian Sea coast as well as Persian Gulf coasts. In general mountains area has experienced more variation in compare with law areas. In regard for trend analyses, spatial distribution of daily trends has been mapped in fig 1. As it is clear almost all over Iran (except in Bandar Abass and Chabahar) decreasing significant trend by -0.000043 to -0.000067 mm/day especially in south as well as southwest of the country has been occurred. Fig 1: Spatial distribution of precipitable water over Iran (Mm/day) In order to survey temporal variation and base on Man-Kendal test has been used. The result is displayed in fig 2. As it is clear since the first year under investigation, trend had decreasing behavior, while it beams significant in 1987. Fig 2: Trend changes in precipatable water over Iran Using Man-Kendal Sequential testThese trends caused by decreasing in water vapor advection also result in increasing in temperature in addition to decreasing of precipitation over Iran.ConclusionSurveying precipitable water over Iran has shown that this climatic parameter is dramatically depending on local as well as global factors. Accordingly the most spatial variations take place in 00:00 and 06:00 o’clock. Trends analyses have shown decreasing significant trend by -0.000043 to -0.000067 mm/day in the country.
https://jphgr.ut.ac.ir/article_52995_6dcf9f35d3f3af2420feaf5883ab400f.pdf
ایران
آب قابل بارش
تحلیل همسازهها
ناهنجاریهای آب قابل بارش
Keywords: Perceptible Water
anomalies
Harmonic Analysis
Iran
per
دانشگاه تهران
پژوهش های جغرافیای طبیعی
2008-630X
2423-7760
2014-12-22
46
4
445
462
10.22059/jphgr.2014.52996
52996
Full length article
توسعة بهینة شبکة بارانسنجی با استفاده از روش کریجینگ و آنتروپی در محیط GIS (مورد مطالعه: حوضة آبریز کرخه)
Optimal Development of Rain Gauge Network using Kriging and Entropy in Geographic Information System (GIS), (Case Study of Karkhe Basin)
حسنعلی فرجی سبکبار
hfaraji@ut.ac.ir
1
هادی محمودی میمند
mahmoodi.gis@alumni.ut.ac.ir
2
سارا نظیف
nazifsara693@gmail.com
3
رحیم علی عباسپور
abaspour@ut.ac.ir
4
دانشیار دانشکدة جغرافیا، دانشگاه تهران
کارشناسارشد GIS & RS دانشکدة جغرافیا، دانشگاه تهران
استادیار دانشکده مهندسی عمران، پردیس دانشکدة فنی، دانشگاه تهران
استادیار دانشکدة نقشه برداری، پردیس دانشکدة فنی، دانشگاه تهران
با توجه به محدودیت امکان توسعة ایستگاههای بارانسنجی، تعیین بارش در تمام نقاط و به تبع آن تخمین دقیق بارش منطقهای امکانپذیر نیست. لذا، باید در انتخاب محل و تعداد ایستگاهها در تخمین بارش منطقهای دقت کافی به عمل آید. در این تحقیق از آنتروپی انتقال اطلاعات و واریانس تخمین بارش منطقهای برای تعیین نقاط بهینة توسعة ساختار موجود شبکة بارانسنجی استفاد شده است. در ساختار پیشنهادی، نقاط دارای حداکثر واریانس تخمین و حداقل آنتروپی انتقال اطلاعات در سطح حوضه کاندید ایستگاههای جدید در نظر گرفته میشود. مدل بهینهسازی برای ترکیب نتایج این دو روش توسعه داده شده و در نهایت موقعیت پیشنهادی تأسیس ایستگاههای جدید تعیین میشود. در ساختار پیشنهادی، از محیط GIS برای ارائة بهتر نتایج تحلیلهای مکانی استفاده شده است. حوضة آبریز کرخه با توجه به اهمیت بالایی که از بعد منابع آبی کشور دارد، مطالعة موردی این تحقیق در نظر گرفته شده است. نتایج بررسیها و تحلیلهای صورتگرفته در این تحقیق نشاندهندة این است که با استفاده از ایستگاههای پیشنهادی در حوضة کرخه که هفده موردند میتوان دقت نتایج تحلیل مکانی بارش را به میزان زیادی افزایش داد.
In the water resources planning and management, rainfall is considered as the main representative factor of region's hydroclimate system. There is a high level of spatial and temporal variability in rainfall events. Rain gauges are used for precipitation measurement in different points of the region. Due to limitations of rain gauges development, it is impossible to measure the exact distribution of rainfall over an area, so it is needed to select the optimal number and locations of the rain gauges in a region. There are several factors that affect the optimal number and location of stations, thus, development of an optimization model for development of rain gauges network is necessary. In this study an optimization model is proposed for determining location of the rain gauges considering the transformation entropy and the regional rainfall estimation error. In this model, the points with the minimum transformation entropy and the maximum rainfall estimation error are considered as candidates for development of new stations. The results of two considered criteria are combined to determine the location of the new stations. Geogrpahic information system (GIS) is used to better represent the results of rainfall spatial analysis and explain results of the proposed optimization model. A sub basin of Karkhe basin in South West of Iran has been considered as the case study of this study. Results show that using new rain gauges which are determined to be 17 using the proposed approach could improve accuracy of spatial analysis of rainfall siginficiantly. Keywords:Variance estimation, entropy, rainguage network optimization, GIS, Karkheh BasinMethodolgoyThis proposed methodology in this study involves the following steps: (1) Data collection and analysis (2) application of kriging to existing rainfall data to calculate the rainfall spatial analysis variance (3) calculating the transformation entropy in the basin surface (4) selection of candidates points for rain gauge development considering the minimum transformation entropy and the maximum rainfall estimation error (5) presentation of rain gauge network final map.In this paper, the best combination of sampling stations in a monitoring network is selected using the entropy theory by considering the maximum uncertainty (minimum redundant information in the system) and the maximum rainfall estimation Kriging error. Hence, in this study, a new model composed of variance estimation and entropy is proposed to relocate the rainfall network and to obtain the optimal design with the minimum number of rain gauges. Results and DiscussionThe rainfall data of the 49 stations in the study region are for the period of October to April are utilized.The correlation coefficient higher than 0.6 in rainfall and height, Cokriging method was used to analyze the spatial rainfall. Kolmogorov Smirnov test (K-S) with a confidence level of 95% of normal monthly precipitation data is verified. In case of non-normal data conversion Cox - Box or log normal distribution, the data are close to normal distribution. The estimated variance is calculated for each month. After calculating variance estimates for each month, the layers can be weighted according to the average rainfall. The final layer of the overlapping layers are obtained and as a measure of the objective function be considered. The transformation entropy layer such as variance estimation layer obtained. A new model composed of variance estimation and entropy is proposed to relocate the rainfall network to obtain the optimal design with the minimum number of rain gauges. As a case study, the application of the proposed method to an existing rain network over the Karkhe catchment region under a minimum transformation entropy of 30% and maximum Kriging error of 60% resulted in 17 new rain stations to be added to the original network.CnclusionsIn this study a methodology is proposed to suggest new locations for rain gauges development using kriging and entropy methods. On the basis of the rainfall data from the current rain gauge stations, the rainfall of the candidate rain gauge stations are generated by estimation Kriging error. The information entropy is based on the concept of probability to measure uncertainties. A network optimization model based on minimizing the estimated variance and by rain gauge data suggest that the implementation of this new model, 17 stations were added to the network location. Most of the stations in the eastern and north-eastern border of the basin, in the highlands and in places where the space station is too high, they were located. The results show that using the theory of Entropy with geostatistical methods, a higher accuracy in rainguage network development, can provid. By combining the two methods can be used to determine the best places established stations, so that the two factors cover each other. Spatial design using model proposed in this paper, the best combination for rainguage stations using the minimum transformation entropy and the maximum rainfall estimation Kriging error is selected.
https://jphgr.ut.ac.ir/article_52996_434cf4f413ec02628d01c6c3cbb72c01.pdf
آنتروپی
بهینهسازی شبکة بارانسنجی
حوضة کرخه
سیستم اطلاعات جغرافیایی
واریانس تخمین
Karkheh basin
Entropy
rainguage network optimization
GIS
Variance estimation
per
دانشگاه تهران
پژوهش های جغرافیای طبیعی
2008-630X
2423-7760
2014-12-22
46
4
463
476
10.22059/jphgr.2014.52997
52997
Full length article
نقش عوامل آبوهوایی در تعیین تاریخ آغاز کشت و طول دورة رشد کلزا با کاربرد مدل CropSyst (مورد مطالعه: استانهای ساحل دریای خزر)
The Role of Climatic Factors in Determining the Start Date of Planting and Growing Period of Colza with Application of CropSyst Model, Case Study: Coastal Provinces of Caspean Sea in Iran
فیروز مجرد
f_mojarrad@yahoo.com
1
بهمن فرهادی
bfarhadi2001@yahoo.com
2
راضیه خیری
raziye.khairy@yahoo.com
3
دانشیار گروه جغرافیا، دانشگاه رازی کرمانشاه، ایران
استادیار گروه مهندسی آب، دانشگاه رازی کرمانشاه، ایران
کارشناسیارشد اقلیمشناسی، گروه جغرافیا، دانشگاه رازی کرمانشاه، ایران
استفاده از متغیرهای آبوهوایی و طبیعی در تنظیم فعالیتهای کشاورزی از اهمیت ویژهای برخوردار است. در مطالعة حاضر، میانگین تاریخهای آغاز و خاتمة دورة بارش اصلی در ده ایستگاهجنوب دریای خزر با استفاده از شاخص درصد تجمعی میانگین بارش کل سال در دورههای پنج روزه (pentads) با نرمافزار Instat محاسبه شد. بر اساس تاریخهای آغاز بهدست آمده از نرمافزار و با استفاده از آمار روزانة عناصر آبوهوایی شامل بارش، دماهای حداکثر و حداقل، رطوبت نسبی حداکثر و حداقل، تابش خورشیدی و سرعت باد در دورهای 26ساله و نیز بهکمک خصوصیات خاک ایستگاهها طول دورة کشت و عملکرد پتانسیل کلزا با استفاده از مدل CropSyst برآورد شد. در نهایت، بر اساس بیشترین عملکرد بهدست آمده از بین تاریخهای مختلف، مناسبترین تاریخ شروع و طول دورة کشت محصول تعیین شد. نتایج تحقیق نشان داد که تاریخهای آغاز دورة بارش اصلی در ایستگاهها از 8 شهریور تا 10 آبان متغیر است و این تاریخها در مقایسه با تاریخهای خاتمة بارش نوسان کمتری دارد. مناسبترین تاریخهای آغاز کشت کلزا در ایستگاهها از 13مهر تا 29 آبان با طول دورة کشت 173تا 209 روز تعیین شد. عملکرد پتانسیل محصول در منطقه با میزان بارندگی رابطة مستقیم و با دوری از ساحل رابطة معکوس دارد.
IntroductionThe use of climatic and natural variables in the regulation of agricultural activities has a particular importance. Of the important characteristics of climate are the onset and retreat dates of main rainy season which have a determining role in the agricultural activities such as seeding time, cultivation period and other agricultural programs and strategies like irrigation. Iran residing in the arid and semiarid region has a variety of climates and consequently experiences high irregularities of spatial and temporal distribution of precipitation and other climatic elements. Southern coasts of Caspian Sea in Iran as a region with the highest precipitation in the country, has good potentials for agricultural activities. Among the most important crops for the development of cultivation in this plain is colza (canola). Since colza can be cultivated under rainfed conditions in high precipitation areas, therefore the analysis of precipitation characteristics in the region on the one hand, and onset and retreat dates of main rainy season in that plain on the other hand, can play an important role in the development of cultivation area.Materials and MethodsAverage onset and retreat dates of main rainy season were calculated at selected stations of the region using an index called “cumulative percentage of mean daily rainfall during the year in 5-day periods (pentads)” with Instat software, and the relevant graphs were plotted. Average onset and retreat dates of main rainy season are the dates of year when 10% and 90% cumulative mean annual rainfall during pentads are obtained respectively. The length of the main rainy season is taken as the time interval between the rainfall onset and retreat. The cumulative rainfall based on pentads is used to decrease the daily rainfall fluctuations during the year, so that the detection of onset and retreat dates of main rainy season is much more convenient. Based on the dates obtained from the software and using the daily data of climatic elements including rainfall, minimum temperature, maximum temperature, minimum relative humidity, maximum relative humidity, solar radiation and wind speed in a 26-year period (1984-2009), and also with the aid of soil properties at the stations, the cultivation period and potential yield values of colza were estimated by CropSyst model. Finally, based on the highest yield obtained from the dates entered to the model, the most suitable planting date and duration of cultivation were determined. Results and Discussion The results of this study showed that the onset dates of main rainy season in the stations vary between 30 Aug to 1 Nov, and these dates have had less fluctuations in comparison with the retreat dates; since the retreat dates have had differences about 50 days, i.e. from 17 Mar in Bandar Anzali in the west to 6 May in Gorgan in the east of the region. The low differences among onset dates of main rainy season in the stations prove the regularity of rainfalls which result from the regularity of rainfall-producing mechanisms in the region. This occurs especially in September as the onset of rainy season in the region and the onset of advection rainfalls originating from Siberian high pressure, particularly around the Rasht and Bandar Anzali. It seems that determining the onset and retreat dates of main rainy season using rainfall amounts leads to more reasonable results than the use of number of the rainy days. Also the length of the main rainy season in the stations varies from 185 days in Manjil to 234 days in Ghaemshahr, which represents a few weeks difference in comparison with the graph illustrated by Sedaghat (2007: 36) regarding the cumulative mean monthly rainfall in Iran. The most appropriate planting dates for colza in the selected stations of the region were suggested from 5 Oct in Manjil to 20 Nov in Bandar Anzali. Relevant cultivation durations in the stations vary from 173 to 209 days. Potential yield of the product in the region shows significant direct correlation with amount of rainfall, and significant inverse correlation with distance from shore.ConclusionRecognition of characteristics of main rainy season and its onset and retreat dates has a determining role in the various activities especially agricultural activities. In this research average onset and retreat dates of main rainy season were calculated at selected stations of coastal provinces of Caspean Sea in Iran using an index called “cumulative percentage of mean daily rainfalls during the year in 5-day periods”. The results showed that the onset dates are more regular than the retreat dates due to regularity of rainfall-producing mechanisms in September. Differences in suggested planting dates in this study and the report of the Ministry of Agriculture can be related to different varieties of colza used in the studies, and different calibrations of models based on the climatic and natural circumstances at the various parts of the country; Hence our special offer for respected researchers in the future studies is to calibrate the CropSyst model with regard to the climatic and natural circumstances of the study area.
https://jphgr.ut.ac.ir/article_52997_fc307df757f1fc83fc89794c5b8b1ce5.pdf
: استانهای ساحلی دریای خزر
تاریخ آغاز کشت
طول دورة رشد
کلزا
مدل CropSyst
Coastal Provinces of Caspean Sea
Start Date of Planting
growing period
Colza (Canola)
CropSyst Model
per
دانشگاه تهران
پژوهش های جغرافیای طبیعی
2008-630X
2423-7760
2014-12-22
46
4
477
494
10.22059/jphgr.2014.52998
52998
Full length article
امکانسنجی نواحی مستعد توسعة اکوتوریسم در شهرستان تالش با بهرهگیری از GIS
Feasibility Study of Ecotourism Regions in Talesh County Using GIS
سعید خدائیان
saeed.kh1332@gmail.com
1
نازنین فکری زاد
nazanin_fekrizad@yahoo.com
2
بهروز ارسطو
beharas2@gmail.com
3
استادیار، ژئومورفولوژی، دانشگاه شهید بهشتی
کارشناسیارشد، مدیریت جهانگردی، دانشگاه سمنان
پژوهشگر سنجش از دور و GIS، مرکز تحقیقات کشاورزی و منابع طبیعی استان سمنان
به منظور اجتناب از پیامدهای نامطلوب گردشگری، توسعة آن باید اندیشیده شده باشد. یکی از اولین اقدامها جهت حصول به این مهم، شناسایی مکانهای مناسب برای توسعة گردشگری و برنامهریزی زمین است که در نهایت به الگوی بهینة توسعة مقصد گردشگری منجر میشود. شهرستان تالش به دلیل برخورداری از جاذبههای کمنظیر طبیعی، از منظر اکوتوریسم دارای پتانسیلهای بسیار مناسبی است؛ اما، متأسفانه عدم مدیریت صحیح گردشگری و توسعة ناپایدار آن، با روندی فزاینده منجر به نابودی این منابع منحصر به فرد شده است. لذا، در این پژوهش با هدف شناسایی پهنههای مستعد توسعة اکوتوریسم بر آن شدیم تا ضمن شناسایی بهترین مکانها، راهکارهایی جهت توسعة پایدار اکوتوریسم در شهرستان تالش ارائه دهیم. بدین منظور با بهرهگیری از ابزار GIS و با استفاده از مدل اکولوژیکی اکوتوریسم برای ایران، پهنههای مستعد توسعة اکوتوریسم شناسایی شد. یافتهها حاکی از آن است که 406 کیلومترمربع از پهنههای شهرستان مناسب برای اکوتوریسم متمرکز و 1541 کیلومترمربع، مناسب برای توسعة اکوتوریسم گسترده است. همچنین، بخش مرکزی از بیشترین توان برای توسعة اکوتوریسم متمرکز و گسترده برخوردار است.
IntroductionTo avoid the adverse consequences of tourism, some decisions must be made about its development. To achieve this purpose, one of the first steps is to identify the suitable regions for tourism development and land use planning which will eventually lead to optimum model of development of tourism destination. Due to having unique natural attractions such as mountains, dense forests, rivers, up-country - historical villages, waterfalls and natural springs as well as beautiful beaches of the Caspian Sea, Talesh County has a very good potential for ecotourism. However unfortunately, the lack of proper tourism management as well as the unsustainable tourism development have led to destruction of these unique resources with a growing trend. As the largest county of Gilan province, this county is located in the west of this province. Materials and MethodsAccording to the intended evaluation features of the research which aims at identifying the ecological capabilities and the regional zoning in terms of ecotourism development capabilities and nature-based tourism planning, the feasibility of the areas of ecotourism of the region was performed by the use of Geographical Information System (GIS) and the ecological model of ecotourism for Iran and with regard to the special conditions of the region. In this survey, the researcher used the Arc GIS 10 software in order to overlay the maps and create the layers. Moreover, she used the information which had been obtained through climatic data (temperature, precipitation, humidity, number of sunny days), topography, vegetation, soil texture, geology and protected areas. The model used in this study was the ecological model of ecotourism of land use development which had been proposed for Iran and had been based on the systemic analysis and multiple criteria evaluation. This model classifies the region into two groups of intensive and extensive ecotourism and each of which are classified and analyzed in two classes. The first class represents the most suitable condition and the second one represents the suitable condition for the development of ecotourism. Results and discussionsTo achieve an optimal model for the evaluation of the ecological potential of ecotourism, in the first step of the research, in this model the effective spatial and descriptive data were collected and then through georeferencing these data and linking them with the descriptive tables, the data layers were created. To achieve this purpose, the researcher used the Arc GIS 10 software. After the data layers were preparing based on data classification in evaluation model, the classified information was obtained. Then, through overlaying the maps, the spatial information was integrated together and based on their ratings, the potential regions for ecotourism development were identified and the extent of which were determined. To overlay the maps The findings suggest that 406 square kilometers of Talesh lands have the potential for development of intensive ecotourism and 1541 square kilometers of Talesh lands have the potential for development of extensive ecotourism. In addition, Markazi district has the most potential for the development of intensive and extensive ecotourism. ConclusionsGiven that the regions which are related to intensive and extensive ecotourism of the first type are mostly seen in plains and coastal areas of Talesh County, these regions have the necessary conditions for the development of water- base and coastal tourism activities as well as the rural tourism and agritourism. The regions which have the potential for intensive and extensive ecotourism of the second type are mostly located in the highlands of the county. These regions have the necessary conditions for the development of the mountain Sports and activities. Due to the existence of Marian and Agh Evlar up-country-Historical villages, the scientific and specialized tours are also recommended in this area. In general it can be concluded that most parts of the county have the necessary conditions for the development of ecotourism and it indicates that Talesh County has a high potential for ecotourism development. It is in such a way that about 19% of the total area of the county (406 square kilometers), is suitable for the development of the intensive ecotourism and 71% of its total area (1541 square kilometers) is suitable for the development of the extensive ecotourism. Moreover, given that Markazi district is of the most regions for the development of two types of intensive and extensive ecotourism, planning for the development of infrastructures and providing programs for tourism development in this region is very essential.
https://jphgr.ut.ac.ir/article_52998_45cb3d3e8595c42408945f3cf89769e6.pdf
اکوتوریسم
امکانسنجی
توسعة پایدار گردشگری
شهرستان تالش
GIS
Ecotourism
Feasibility
Sustainable Tourism Development
Talesh County
GIS
per
دانشگاه تهران
پژوهش های جغرافیای طبیعی
2008-630X
2423-7760
2014-12-22
46
4
495
508
10.22059/jphgr.2014.53000
53000
Full length article
ارزیابی روشهای تحلیل شبکه (ANP) و تحلیل چندمعیارة مکانی در بررسی پتانسیل وقوع زمینلغزش در محدودة محور و مخزن سدها (مطالعة موردی: سد قلعهچای)
Assessment of Analysis Network Process and Heuristic Method in the Investigation of Landslide Potential in the Axis Range and Reservoir Dams
(Case Study: Ghalea Chai Dam)
شهرام روستائی
roostaei@tabriz.ac.ir
1
لیلا خدائی قشلاق
khodaeileila@yahoo.com
2
فاطمه خدائی قشلاق
khodaeifatemah @yahoo.com
3
استاد گروه ژئومورفولوژی، دانشگاه تبریز
کارشناسیارشد سنجش از دور و GIS، دانشگاه تبریز
دانشجوی کارشناسیارشد هیدروژئومورفولوژی، دانشگاه تبریز
ارزیابی پتانسیل وقوع زمینلغزش در منطقهای که به دلیل وضعیت جغرافیایی و ساختوسازهای انسانی مستعد لغزش است ضروری است. سد مخزنی قلعهچای عجبشیر یکی از این نوع نواحی است. در این مطالعه، به منظور بررسی پتانسیل وقوع زمینلغزش روشهای تحلیل شبکه (ANP) و چندمعیارة مکانی ارزیابی شد. در این مطالعه از تصویر TM، 2011 ماهوارة لندست استفاده شد. فاکتورهای مؤثر بر وقوع زمینلغزش (شیب، جهت دامنه، لیتولوژی، کاربری زمین، فاصله از گسل، فاصله از رودخانه، فاصله از جاده، طبقات ارتفاعی) در محیط GIS آماده و سپس با لایة پراکنش زمینلغزشها قطع داده شد و نقشههای پهنهبندی خطر زمینلغزش در روشهای فوق تولید شد. نتایج نشان داد که در بررسی پتانسیل وقوع زمینلغزش در منطقة مورد مطالعه، فرایند تحلیل چندمعیارة مکانی نسبت به روش فرایند تحلیل شبکه عملکرد بهتری دارد. همچنین، تفسیر ضرایب نشان داد که کاربری اراضی، طبقات ارتفاعی و جهت دامنه نقش مهمی در وقوع زمینلغزش دارد و با استفاده از نقشة پیشبینی احتمال وقوع زمینلغزش، منطقه به پنج گروه حساسیت بسیار پایین، پایین، متوسط، بالا و بسیار بالا تقسیم شد.
Extended AbstractIntroduction:Natural disasters management requires local information in order to be ready against dangers and reduce their procedure. Hence, evaluation of landslide occurrence in the area which is prone to landslide due to geographical condition and human constructions is high crucial. Ghale Chai dam located at Ajabshir Watershed is one kind of such areas. So the aim of present investigation is to identify hillside instabilities and movements and their influencing factors to prevent their harmful effects on natural resources and other parts of economical and engineering development and recognize points with high prone of danger. Hence, the aim of present investigation is to assess analytical network process and Heuristic method in determining the landslide prone areas in range axis and reservoir of Ghale Chai dam of Ajabshir.Methods and Materials: The efficiency of network analysis process and logistic regression method were studied to investigate landslide potential in studied area dam. ANP model building requires the definition of elements and their assignment to clusters and a definition of their relationships (I.e. the connections between them indicating the flow of influence between the elements). Like AHP, ANP is founded on ratio scale measurements and pair wise comparisons of elements to divide priorities of selected alternatives. In addition relations among criteria and sub-criteria are included in evaluations, allowing dependencies both within a cluster (inner dependence) and between clusters (outer dependence) (Saaty: 2001). Pairwise comparison is now done, both for weighting clusters (criteria) and for estimating the direction and importance of influences between elements, numerically pictured as ratio scale in a so-called super matrix. Network analysis process was used for the first time in Iran in order to evaluate landslide, done using super decision and arc GIS software. However, to assess landslide susceptibility using heuristic method there are two common approaches: direct and indirect method. The first method applies direct assessment to interpret susceptibility in the field on the basis of detailed maps (geomorphological maps, for instance). The latter does not assess directly in the field, but via data integration techniques in any particular software. This study uses indirect heuristic method. Heuristic approach is a semi-qualitative method. Besides uses knowledge properties (expert opinions, previous research results or literature recommendations), it also uses index-based procedures such as simple ranking and rating or analytical hierarchy process (AHP) in assigning weight and creating model. Concerning this, scoring and weighting process are crucial to build a model in heuristic approach.Results and Discussion:Considering research questions, a three-layer network model composed of target layer, criteria layer and options layer was designed and organized in network analysis process. The priority of danger classes was determined based on their coefficients after doing paired comparisons among elements and clusters. Zoning map was classified in five classes from very high to very low. The weighting judgment process in pair-wise comparison gives a weight for every Influencing factor. From the calculation, the final criteria tree (with weight in 2 digits) was created. Bigger weights indicates that, the pertinent factor gives bigger influence toward the model .Aspect has the biggest contribution (0.2519), followed by distance to road and litology with value 0.1786 and 0.1747, respectively. On the other side, the lowest contribution is given by slope (0.0387), followed by Dem (0.0590). No negative weights in heuristic method. The inconsistency value is 0, 0 62194: smaller than 0, 1. It means, according to SMCE validation, the choosing process is consistent. No improper stage while positioning the factor based on its importance to another After running paired comparisons between elements and clusters the priority of the danger classes based on their significance was determined and the coefficients of the factors showed that the aspect factor has the maximum effect in occurrence of the landslides if the area .the zoning of map were classified in five classes of very high to very low risk classResults:Results obtained from this investigation indicated that from eight influential factors of landslide occurrence in the area, land use, height classes and domain direction have the highest influence in landslide occurrence. Moreover comparisons of distributed landslide proportion degrees with zoning maps of above mentioned models indicated that Heuristic model with 86.25 percent of proportion had better performance than network analysis. So from two statistical models obtained from two methods used in this study, statistical model obtained from Heuristic method administration (2nd equation) is selected and introduced as the best model. Moreover, considering results obtained from landslide danger zoning in studied area, using two early mentioned methods, it was conclude that 67.33% of zone total area has very high danger of landslide occurrence. Keywords: Ghale Chai Dam, Analytic Network Process (ANP), Heuristic method, Landsat Satellite, Landslide.
https://jphgr.ut.ac.ir/article_53000_918587653536dfa6e0910c6edce93308.pdf
سد قلعهچای
تحلیل شبکه (ANP)
تحلیل چندمعیارة مکانی
ماهوارة لندست
زمینلغزش
Ghalea Chai dam
Analytic Network Process ( ANP )
Heuristic method
Landsat satellite
landslide
per
دانشگاه تهران
پژوهش های جغرافیای طبیعی
2008-630X
2423-7760
2014-12-22
46
4
509
524
10.22059/jphgr.2014.53001
53001
Full length article
واکاوی همدید رخداد سیلاب آبانماه 1390 در شهرستانهای بهبهان و لیکک
The Synoptic analysis of flood occurrence on November 2011 in Behbahan and Likak cities
فرامرز خوش اخلاق
fkhosh@ut.ac.ir
1
رضا صفایی راد
rezasafaierad@yahoo.com
2
داود سلمانی
salmanidavoud@yahoo.com
3
استادیار دانشکدة جغرافیا، دانشگاه تهران
دانشجوی دکتری اقلیمشناسی، دانشکدة جغرافیا، دانشگاه تهران
کارشناسارشد اقلیمشناسی، دانشکدة جغرافیا، دانشگاه تهران
در پژوهش حاضر به منظور واکاوی همدید سیلاب 29 آبان 1390 (20 نوامبر 2011) که در شرق خوزستان و غرب کهگیلویه و بویراحمد رخ داد، تغییرات الگوهای همدید در نقشههای سطح زمین و تراز 500 هکتوپاسکال از دو روز پیش از رخداد سیلاب تا یک روز پس از آن واکاوی شد. بررسیهای انجام شده نشان داد که تشکیل و گسترش مراکز کمفشار مدیترانه- سودانی بهدلیل قرارگیری بین مراکز پرفشار اروپا و پرفشار جنب حارهای جنوبشرق عربستان، سبب تشکیل کمربند همگرایی روی سودان و دریای سرخ میشود. وجود دو مرکز پرفشار یادشده بهترتیب سبب فرارفت هوای سرد و گرم به درون کمربند همگرایی دریای سرخ و سامانة سودانی میشود و موجبات تقویت آن را فراهم میکند. همچنین، وجود ناوه عمیق شمال آفریقا که محور آن از شرق مدیترانه تا شمال سودان امتداد دارد، سبب تشدید تضاد دمایی در ترازهای بالای جوّ و پویایی بیشتر این سامانه شد. قرارگیری منطقة پژوهش در خروجی جتباد جنبحارهای نقش مهمی در تقویت و عمیق شدن کمفشار مدیترانه- سودانی و حرکت شرقسوی آن داشته است. در این شرایط آرایش الگوهای همدید به نحوی بود که منجر به ورود رطوبت از منابع رطوبتی دریای عرب، دریای سرخ و خلیج فارس به منطقة پژوهش شد و سبب شد تا در روز بیستم نوامبر در منطقة پژوهش بارش شدید و در نهایت سیلاب رخ دهد.
Extended AbstractIntroduction The Recognition of behaviors of the atmospheric circulation patterns and effective climatic elements in occurrence of flood is very important, especially because abnormal climate changes such as global warming in recent years tend to change in atmospheric circulation patterns and outbreak climatic inelegances in many areas in the world. Intensive and torrential precipitations in anomalous time and space is very important for a country like Iran with specific climatic characteristics and is always among the factors which in different geographical regions has some irrecoverable effects on humans life and finance and has affected human beings and nature widely .The south-west region of Iran that has been located in the windward slops of Zagros mountains and in the path of westerlies and rainbearing air masses, is among the regions which due to different atmospheric circulation patterns and receives heavy precipitations and is exposed to destructive floods. That flood of 20 November 2011 which has occurred in Khuzestan and Kohkilou-e-va-buyer-Ahmad provinces is obvious among them. This flood imposed many death tolls and caused a big mass of financial damages to those regions. Coordination before occurring accidents and hazards is the key factor in crisis management. Therefore identification of flood causing patterns and their punctual prediction can facilitate better management of crises and hazards and minimize mortality and financial damages caused by these type of natural disasters.Materials and methods This flood in the study area created by an extreme storm in western and southwestern regions of Iran. In order to analyze the synoptic pattern of this flood, the data of sea level pressures, surface wind directions, surface temperatures, geopotential heights of 500 Hpa and specific humidity and wind directions of 850 and 700 hpa and data representing omega values from NCEP/NCAR website has been collected and then synoptic maps were drawn by using GrADS software which were related to 2 days before flood until a day after that. Then the causes of flood were revealed by synoptic analysis of the maps.Result and discussion Analysis of synoptic maps reveals role of some systems in creating the flood. By positioning the pressure center of Sudan low between European high pressure and Arabian subtropical high pressure has been resulted to form a convergence belt over the Sudan and the Red sea. European high pressure caused the advection of cold air from high latitudes and in other hand, Arabian subtropical high pressure caused to advection of warm and humid air from low latitudes into the Sudan low - Red sea’s convergence belt. Convergence of northern cold air and southern warm air in this belt, tend to intensify the belt. Gradually, with intensification of the system and its NE move, the convergence belt lied over SW regions of Iran. Pressure map of 500 hp shows a deep trough in North Africa. This trough intensifies temperature gradient in upper levels of the atmosphere and following of this event, the trough becomes deeper and its axis lies over the Red sea. Analysis of specific humidity and wind direction maps of 850 and 700 hpa indicated that the humidity sources for the rainfall systems were the Red sea, Arabian Sea and Persian Gulf in 850 hp level and Red sea and Persian Gulf in 700 hp level. Conclusion Locating Sudan low pressure between Arabian subtropical high pressure and European high pressure tends to create an air convergence belt with SW-NE trend from Sudan to north of Arabian Peninsula. Cold Advection from European high pressure and warm advection from Arabian high pressure finally intensify temperature and pressure gradients in the convergence belt and the transformed the system into a dynamic system. In result of advection of cold air to back part of the system, its eastward movement became faster and pull the system over SW areas of Iran. Movement of cold air in back part of the system caused an extreme updraft of air and generated a severe rainfall. The Arabian subtropical high pressure provided required humidity for this rainfall from warm waters of Red sea and, Arabian Sea and Persian Gulf into the system and eventually resulted in a heavy rainfall that in a short time generated the disastrous flood with abundant damages in study area.
https://jphgr.ut.ac.ir/article_53001_dc9cf14791d7321485210a9be8273497.pdf
آبوهواشناسی همدید
سیلاب
پرفشار جنبحاره
جنوبغربی ایران
کمفشار سودانی
synoptic climatology
Flood
Sudan Low pressure
subtropical high pressure
Southwest of Iran
per
دانشگاه تهران
پژوهش های جغرافیای طبیعی
2008-630X
2423-7760
2014-12-22
46
4
1
20
10.22059/jphgr.2014.53328
53328
چکیده های انگلیسی
English Abstracts
https://jphgr.ut.ac.ir/article_53328_0236c2768e145cb0ade499dba6924f16.pdf