فصلنامه پژوهش های جغرافیای طبیعی
پیاپی 75 (بهار 1390)

IntroductionClimate is among the most important factors affecting vegetation condition. AVHRR-NDVI data are used to evaluate climatic and environmental changes at regional – as well as global - scales. Since 1983, Advanced Very High Resolution Radiometer (AVHRR) of the NOAA satellites gave a continuous spatial cover on a regular time scale of the photosynthetic activity, which can be expressed by indices such as the Normalized Difference Vegetation Index (NDVI). The NDVI, defined as the ratio (NIR-VIS)/(NIR+VIS), represents the absorption of photosynthetic active radiation and hence act as a kind of measurement of the photosynthetic capacity of the canopy. Previous studies indicated that there was a significant relationship between AVHRR-NDVI and precipitation or temperature. For example, in the northern Great Plains, many researchers have found close relationships between AVHRR-NDVI and climate, especially precipitation. Various studies (Yang et al 1998, Richard & Poccard 1998, Wang et al. 2001, Ji & Peters 2004, Li et al 2004) found significant correlations between NDVI and rainfall in different regions, including arid and semi-arid environments.In Iran, researchers assessed only relation between drought and NDVI. For example, Taherzadeh (2007) has been studied relation between NDVI and Standardized Precipitation Index (SPI) in the Minab basin. The results of that study showed that there was a good relationship between SPI and NDVI, but there was a negative relation between Land Surface Temperature (LST) and SPI, as well (Taherzadeh, 2007, 173).Shamsipour (2007) has studied drought for the Kashan area using NDVI and VCI. The results of that study showed that there were almost suitable relations between NDVI and VCI with meteorological methods. According to product of utilization NDVI and VCI, the years 2000 and 2001 were with drought condition, and the years 2002 & 2004 were with wetness (Shamsipour, 2007, 1).MethodIn this research, the authors analyzed the relation between vegetation density and the monthly climatic variables of rain, relative humidity (Mean, Max., and Min.), and temperature (Mean, Max., and Min.) in the dense pastures (75-100 percent) of Iran. The climatic data were obtained from the Meteorological Organization of Iran for 134 stations (October2005- October 2006) and vegetation density was extracted from AVHRR-NOAA satellite as the NDVI index for January to October 2006. The vegetation layers (forest and pasture) were obtained from the Forest Organization of Iran, than divided to layers based on density. The authors analyzed AVHRR-NDVI and seven climate variables, using a Multivariate Ordinary Least Squares regression (MOLS) technique. The maximum value composite (MVC) is calculated from a multi-temporal series of geometrically corrected NDVI images. The common maximum NDVI value composite (MVC) method was used to compile monthly NDVI dataset. The maximum value composite method could minimize atmospheric effects, scan angle effects, cloud contamination and solar zenith angle effects.Results and Discussion For interpolation the climatic variables, the researchers applied geostatistic methods such as Inverse Distance Weighting, Kriging, and Co-Kriging. In most of the variables, Co-kriging method showed the lowest of errors; but the mean temperature showed reliable results with IDW method. On the over all, in interpolation the climatic factors with CO-Kriging method results showed that best R2 between observed and predicted values for precipitation, maximum, minimum temperature, maximum, mean and minimum relative humid are 0.436, 0.93, 0.863, 0.672, 0.741 and 0.703; but for mean temperature R2 is 0.881 in IDW method. Previous studies using both observation and simulation models showed that there was a complicated lag effect between vegetation and climatic variables. Lag time was an affect of climatic factors on the vegetation growth, which the lag time varied from several days to 1 year - or even longer. For example, obtained results by researchers i.e. Potter and Brooks (1998) showed lag times of 1 to 2 months for maximum and minimum temperature and rainfall. Conclusion In this paper, the authors obtained the lag time for the vegetation growth response to the climatic factors, two months for rainfall and one month for the other variables.In most of the variables, Co-Kriging method showed the lowest errors; but the mean temperature showed reliable results with IDW method. The results showed that the relation between NDVI was higher relative humidity (mean and max) and maximum temperature, but lower for the rain and minimum temperature. The effect of the warm season climate was higher than that of the cold season. The highest relation of 0.78 was experienced in October, and the lower 0.23 value was computed for January.

IntroductionPrecipitation is one of important climatic elements that vary considerably over space and time. One of the important aspects of precipitation study is the extreme precipitation. Because of economical effect, in recent years extreme climatic events have proved to be one of the most popular topics in contemporary climatology. It is well understood that climatic features in precipitation records are hidden in relative variables such as monthly and annual precipitation amounts, 24-hour annual precipitation extremes, rainfall intensities and temporal scale of rainfall variation ranges from minutes in a storm cell to decades and longer. The variability and spatial distribution of precipitation at different scales are the main cause of flood and drought events. For analysis of variability of precipitation, we can use harmonic method. Harmonic analysis is a particularly useful tool in studying precipitation temporal patterns as it reveals the spatial variation of various precipitation characteristics. It delineates the geographic extents of various precipitation regimes and highlights the boundaries between them.Materials and MethodsNorth of Iran as a particular region has very different climatic condition. Harmonic analysis with the aid of forty years data of the well distributed network of 32 stations used to study of precipitation variability at this region. A brief explanation of the principles of harmonic analysis is presented concerning the nature and interpretation of this technique.For the monthly values of the examined frequencies ft (f_t=0 At the origin), harmonic analysis can be written as follows:(f_t) ̂=f ̅+∑_(k=1)^6▒(A_k cos⁡〖2π/12〗 kt+B_k sin⁡〖2π/12〗 kt) (2)Where A_k, B_k are the coefficients of the kTh harmonic (k=1, 2. .. 6). These coefficients are given by (Panofsky and Brier (1958) and Wilks (2006)) asA_k=1/6 ∑_(t=1)^6▒〖f_t cos(2π/12 kt) 〗 (3)andB_k=1/6 ∑_(t=1)^6▒〖f_t sin(2π/12 kt) 〗 (4)Where f_t represents the monthly frequency of the annual 24-hour maximum precipitation amounts at the tTh month. The amplitude of a given harmonic isC_k=[〖A_k〗^2+〖B_k〗^2]^(1/2) (5)The variance of each harmonic can be calculated (Livada et al. 2008) as:V_k=(C_k^2)/2 (6) And the percentage of variance (PVR(k)) of each harmonic can be determined by the ratio:PVR(k)=V_k⁄(∑_1^6▒〖V_k 〗) (7)The phase angle of the th harmonic can be obtained (Wilks 2006) by:ϕ_k={█(tan^(-1) (B_k/A_k),〖 A〗_k>0 @tan^(-1) (B_k/A_k)±π,or±〖180〗^°,A_k<0@π/2,or 〖90〗^°, A_k=0) (8)┤And the date of the occurrence of the maximum of each harmonic is given by (Livada et al. 2008):T_k=(12/360k) ϕ_(k) (9)Results and DiscussionWith aim of 32 stations harmonic analysis of the inter-annual variability of the frequency of month-to-month monthly maximum precipitation for north region of Iran was applied. With the separation of the data into orthogonal components, in the form of harmonics, the variation of the data can be explained. Harmonic analysis produces the maximum and minimum occurrence instances along a time axis. Normally in the monthly data, six harmonics are adopted for application, but in practice, the first three harmonics are used over the western and central parts of region, in order to explain the variability of the examined annual frequency patterns of the monthly maximum precipitation amounts. First harmonic PVR(1) value at the western part of this area is high Generally the PVR (1) values decrease from north to south and west to east. With increase the distance of sea and costal area PVR (1) values decrease.Second harmonicThe spatial pattern of the second harmonic over area shows that the effectiveness of the second harmonic is the same at most part of northern IranThird harmonicThe spatial pattern of the third harmonic shows over the eastern parts of this region three or more harmonics are needed to describe the month-to-month variation of precipitation frequencies.AmplitudesThe amplitude of the first harmonic describes the natural variation in a single cycle. Amplitude charts show the spatial distribution of the size of particular types of seasonal variations. The amplitude of the first harmonic describes the tendency towards a single annual variation in the observed frequency curves. High amplitudes occur over coastal parts of western part of area. With increasing longitude a reduction in amplitude of first harmonic is observed.ConclusionThe main results of the estimated percentages for the first, second and third harmonics, as well as the amplitudes and the phase angles, are plotted as contour charts from which the following conclusions can be drawn: the first harmonic at this region explain more variances after first harmonic second harmonic has more role for explain of variances Over eastern parts that precipitation occurrence is chaotic, values of PVR(2,3,4) explain the variance time of first harmonic varies from October to April Generally yearly cycle is dominant variability in maximum monthly precipitation at the most parts of this region.

IntroductionMeanders are among beautiful landscapes as well as hazardous geomorphologic - hydrological forms on floods plain in mountainous areas. River meanders are major factors responsible for creation, development and or on the surface of the Earth and have long fascinated people by their apparent regularity. They play a major role in floodplain construction and evolution and are major components of the fluvial landscape. Thay can be highly dynamic features and so pose practical problems associated with channel movement. Many movement meanders and lateral movement of rivers channel. The floods and the excess of energy on rivers bed are main causes for creation of these phenomenons. Meanders are the signs of flood hazards in occurrence area. Shor river (from 36° 05' to 37 °20' N and from 46 °43 to 47° 15' E) have many curvatures on length of channel rivers. This river have typical meander in many parts of the channel.Materials and methods In the present study, changes in channel morphology along the Shor River floodplain were investigated using areal and satellite photographs. And then rate of sinuosity of channel is calculated by index of sinuosity. In this article, in order to investigate the meanders and with aim of study on rate of flood hazard, LFH index has been used. In this study some parameters of meander, for example, wide of channels and belts of meanders have been used too, … In order to investigation on flooding risk on all lengths of channel of Shor River, the channel is shared to 21 segments. All accessory calculations are made in these segments. For investigation on flooding potential of river channel, the parameters of channel curvatures and meandering of course river flow have been used.Also for calculating of flood potential, because of lack data and information by using of different index and coefficients, we explain the situation of flooding in different part of region. Indexes that use in this research are basin relief, drainage density, roughness number, constant of channel maintenance, stream frequency, texture ratio, form factor, elongation ratio. for calculation of flood potential on meandering course of river, we use different experimental equation such as Villiams equation and flood way reduction by using of actual meander amplitude (Aact) and The possible largest meander (Amax). Local flood hazard (LFH) is very important index for calculating risk of flood hazard in meandering river. equilibrium between FR and CA calculate for access to local flood hazard (LFH). in this research by using of meander length, average of debit calculated. For calculating of meander length we use satellite images. Also by using of meander arc and arc angle and width of channel, relation between them calculated. For measuring of parameters mentioned above, we use aerial photos on 21 segments of Shor river.Results and Discussion The results of this study suggested that LFH in length of river channel is very varying. The average of LFH is 0.77. This means that the potential of flood hazard in many parts of channel meandering on Shor river is high. Movement of curvature of meander to lateral of flood plain is cause of increase the bank erosion in length of Shor river and increase of hazards in flood plain. The results suggested also, Rn in Shor basin is high. These results show that the Shor basin treated by flood. Curvature of meanders experiment flooding and since flood Crossed on curvature, channel of river lateral movement. Lateral movements cut the banks and are amang the major causes of the increased sediment. The structures are located near the banks, due to the curvature movement, so the risk of this structure is too high, because flooding and lateral erosion. Also the result show that the first order of drainage network in Shor river is higher than other order or steps. For this reason more tributary reach to higher order and can discharg more runoff to higehr order.ConclusionMany parts of meandering of Shor River have high potential flooding. The results of the study show that this river experiments floods every years. When flood is occurred, curvature of courses is movement. These movements are widening the floodplain. This widening is made by cutting of bank. These movements are very hazardous for the structures which are located near the river channel. The lateral erosion increases when the curvature moves into the bank of channel.

IntroductionSince 1960s, heat balance models of the human body have become more and more accepted in the assessment of thermal comfort. The basis for these models is the human energy balance equation. One of the first as well as still among the most popular heat balance models is the comfort equation defined by Fanger (1972).Climate and tourism have a great dependence to each other, so that existence of a desirable weather condition is an advantage and potential for tourism, and most of the travelers notice to weather conditions in selecting their travel place and time. Climate comforting conditions usually are expressed by indexes which a series of meteorological, human and environmental factors have been played important roles in, and the possibility of comparison among different places is provided by.Comfortable climate condition generally state by indexes that involve the sets of meteorology, humanities and environmental elements. Several thermal indices such as Predicted Mean Vote (PMV), Physiologically Equivalent Temperature (PET) and Standard Effective Temperature (SET*) may be calculated for the assessment of human bioclimatic in a physiologically relevant manner as shown in several applications (Matzarakis et al., 1999; Blazejczyk, Matzarakis, 2007; etc). All indices have the known grades of thermal perception for human beings and physiological stress (Höppe, 1999). PET is defined as a certain air temperature related to fixed standard indoor conditions at which the heat balance of the human body is maintained with core and skin temperature equal to those under the conditions being assessed. In this research, PET index has been used for several cities in different locations in Iran. Material and MethodsIn this research, touristy cities including Mashad, Rasht, Isfahan and Kish Island have been selected for comparative of comfortable climatic condition. In this research, the authors have used the PET index.The Munich energy balance model for individuals” (MEMI) (Höppe 1993) is one of the thermo-physiological heat balance models. It is the basis for the calculation of the physiologically equivalent temperature (PET).In detail the MEMI model is based on the energy balance equation (9.1) for the human body: M +W + R +C + E D + E Re + E Sw + S = 0The individual heat flows in Eq. 9.1, are controlled by the following meteorological parameters (Verein Deutscher Ingenieure 1998; Höppe 1999):- Air temperature: C, Ere – Air humidity: ED, ERe, ESw – Wind velocity: C, ESw – Mean radiant temperature: RThermo-physiological parameters are required in addition:- Heat resistance of clothing (clo units) – Activity of humans (in Watt)The following assumptions are made for the indoor reference climate:1– Mean radiant temperature equals air temperature (Tmrt = Ta). 2– Air velocity (wind speed) is fixed at v = 0.1 m/s. 3– Water vapor pressure is set to 12 hPa (approximately equivalent to a relative humidity of 50% at Ta = 20°C).The calculation of PET includes the following steps:Calculation of the thermal conditions of the body with MEMI for a given combination of meteorological parameters.And then Insertion of the calculated values for mean skin temperature and core temperature into the model MEMI and solving the energy balance equation system for the air temperature Ta (with v = 0.1 m/s, VP = 12 hPa and Tmrt = Ta).In this research, the requirement data have been used in the long-term period on the daily scale. The calculations of PET index have been done using Reymen 2.1 software. Results and Discussion The length of Climatic comfort period which is recommended to be the best time for tourism affairs is 35 days of a year in Mashhad and Esfahan, 37 days in Rasht and 85 days in Kish. The most important tourism limitation for Mashhad, Esfahan and Rasht cities is the existence of excessive cold stress during months Azar (November 22 until December 21), Day (22 December until 21January) and Bahman January 22 until February 21). The results of this research show that duration of climatic comfortable period in the selected cities is short and is located in the separated period on the early spring and autumn. Between of selected cities, Kish island in the cold months of the year and spring season has been the best comfortable climatic condition. The cold stress in the duration of cold season has been main limitation for Mashad, Isfahan and Rasht. Among the selected cities, Kish island has been the best comfortable climatic condition that can recommend for the entire travelers in the early spring. Isfahan town that is one of the most Famous Iranian touristy cities only during the months Ordibehesh (April 22 until May 21) and Mehr (September 22 until October 21) have suitable condition for traveling. ConclusionAccording to the results of this research, comfortable climatic period in the studied cities is short and is located in the second separated periods in the early of autumn and spring. The length of this period, in Isfahan, Mashhad, Rasht and Kish is 35, 35,37 and 85 days of years respectively. Result comparatives of this research show that the best destination for spending of Nowrooz holidays as well as winter travelling is Kish Island. For summer travelling, only Mashhad and Rasht cities have nearly suitable conditions on the second half of September.

IntroductionInvestigating the trends of hydroclimatic components as a result of climate change has been an interesting task for the scientists and water resources managers. So far, numerous case studies have been conducted to exploit the possible trends in temperature and precipitation which imposed by climate change events. Unfortunately, there is a few research works to address the long term variations in some hydrometeorological components such as evaporation and evapotranspiration, perhaps for their complexity. Majority of the recent studies in America, China, India and Australia have reported a decline (reducing) trend in reference evapotranspiration (ET0). The downward trend in pan evaporation and evapotranspiration over most of the United States and former Soviet Union implies that, for large regions of the globe, the terrestrial evaporation component of the hydrological cycle has been decreasing. One explanation is that increased global cloudiness, especially low cloud cover, would be an expected consequence of higher global temperatures. Some increases in annual mean cloudiness have been observed over Europe, Australia, the Indian sub–continent and North America. When cloudiness over the oceans is also considered, it is not possible to be confident that average global cloudiness has really increased. The main purpose of this article is to explore the possible trend in daily ET0 in some selected sites located in warm regions of Iran. The assessment of trend in daily ET0 would be an important tool for the decision makers in water resources engineering and agriculture sectors.Data and MethodsThe authors have used a 50-year (1957-2006) dataset of the observed meteorological variables (mean of daily maximum temperature, mean of daily minimum temperature, relative humidity, wind speed, water vapor pressure, dew point temperature, and air pressure) which recorded in 13 synoptic sites (IRIMO, 2007) during the period of study. Prior to the analysis, all datasets were tested for quality check and gaps. The annual and seasonal trends of ET0 were derived by Mann-Kendall Test and Sen's estimator as non-parametric methods. To compare the daily means of ET0 (50-year and 16-year), Mann-Whitney test was applied. For each selected site, the 50-year ET0 trends were compared against the ET0 trends of 16-year (1991-2006) period. The trend analysis from Sen's method was capable to perform better results, because of eliminating the effect of repeating data in ET0 time series.Results and DiscussionThe either tests (Mann-Kendall and Sen) confirmed that the maximum and minimum significant trends (annual and seasonal) have occurred in summer (47% of total stations) and winter (7% of total stations), respectively. Therefore, the first hypothesis of the study (the existence of significant trend in ET0 values was confirmed. The comparison of the trends in different climates showed that the slope of the ET0 trend during the recent 16 years (1991-2006), which is slightly greater than that of 50-year (1957-2006), has the same overall sign (negative) for most of the stations. As a result, the second hypothesis of the study (the existence of similar trends in recent decades) was also confirmed.Main Findings and ConclusionsIn general, 65% of the stations revealed a negative (decline) trend in ET0 time series at the specified significant level (P< 0.05). The highest and lowest slopes of ET0 were observed for summer (-4 mm/year) and winter (2.56 mm/year), respectively. The comparison of the ETo trends for 50-year period with those of 16-year period presented a good consistency. The results obtained for 16-year analysis showed that 67% of the study sites have experienced negative trends. This suggests that a higher number of sites had the chance to experience reduction in annual ET0 during the recent years. Trend analysis of Mann-Kendall and Sen methods were generally in good agreement. It was shown that 47% of the case studies have no significant trend (positive and negative) in reference evapotranspiration values. In seasonal scale, summer seasons experienced higher number of significant ET0 trends, in comparison to other seasons. This result is in good agreement with most findings from other research works reported from outside Iran. The detection of trends in ET0 for other climate types is required for a national comprehensive work. Further study is also required to find out the reason for different trend signs.

IntroductionArchaeology as a scientific system is indeed indebted to geography for processing of models and comparative studies on reconstruction of paleo-environments and paleo-landscapes, as wall as the patterns of human settlement. It is obvious that different types of existing settlements on the earth are the results of consequential interaction between human behaviors and environmental situation. This communication is obviously clear, in particular, in the case of soil and sedimentary lands, which are very important elements for husbandry and food production. Human impressibility of environment has always been the main reason for spatial differences of settlement and population aggregate and has caused the formation of specific settlement pattern in the ancient times. The aim of this paper is focusing and analyzing the role of natural and geographical elements as well as the environmental in appearance the human settlements in different periods of Mazandaran provinces in Northern Iran. In this region the Alburz chain, such a high natural wall with approximately 70Km wideth, extends from West to East of Mazandaran until Gorgan valley. While the natural and geographical conditions of Mazandaran province prevent easily access to the mountainous area located in the south part of Caspian Sea, it is also causes many problems to investigate and explore the evidence of human remains at this region. The other reason for deficiency of information about the ancient settlement situation of Mazandaran province acts as a kind of limitation for archaeological research in the region. Thus, the initial action for the purpose of this research was archaeological study.Materials and MethodsTo conduct the research, the methodology applied for data gathering will pervasive surface survey. Accordingly, all archaeological and historical remains will be identified and then record in details. The collected data, including 2475 sites and monuments from Neolithic to late Islamic period, were reported in 21 volumes. Dating the sites have been carried out based on sample recognition and comparing studies of collected surface data. The material gathered were divided into four general groups: prehistoric period, Iron Age, historic period and Islamic are. According to current research, from the total 2475 sites, 123 of them belong to pre-history periods, 256 of them belong to Iron Age, and 648 of sites present the culture of the Achaemanid, Parthian and Sassanian era. Finally, 1986 sites and monuments have shown the traces of the Islamic period which some of them show only a particular time of Islamic era and mostly present the monuments and architecture of this period.Results and Discussion For achieving the considered goals, the authors have implemented and analyzed geographical information, using Arc GIS 9.2 software and then, for interpretation of data, SPSS 11.5 software was applied. By establishing a data bank for the study, which is in the form of geographical information system, they carried out an analysis on spatial distribution of the sites. Thus, they focused on natural factors such as height, climate, flowing waters, rivers, flora (forest and pasture), and rainfall to understand the role and efficacy of each factor in appearance of the sites. The study made it clear that the ancient settlement patterns of Mazandaran was highly affected by natural factors such as flora, water sources, rainfall, and climate. ConclusionIn addition, according to this research it has been specified that each natural factors have played different roles in distribution of the ancient sites and there is no the same precept for all. Thus, it is necessary that the role of each natural factor to be studied separately. Among the natural factors studied in this research, there are a positive and meaningful connection between distribution of the sites and the area of the raining layers, distance to the river, flora (forest and pasture). However, there is no significant relationship between the area of the layers of the height and climate, and the distribution of ancient sites.

IntroductionThe Zagros fold-thrust belt in SW Iran is a part of the Alpine-Himalayan system whichconsists of a variety of structures with different sizes or geometries. Morphology of the Zagros Mountains is too complicated, because of impaction of different basement faults during the orogeny. The Izeh fault (N-S trending) is one of these deep-seated faults which its movements had been modified sedimentation patterns and deformation styles of geological units in the Central Zagros. Moreover, it's expected that hydrocarbon migration and accumulation in SW Iran had been affected by this fault system. This paper presents new findings concerning deformation style and mechanism of the Izeh fault. Inasmuch as the RS (Remote Sensing) imagery is one of the valuable means available to geologists for locating geological/ geomorphological features expressing regional fault or fracture systems, therefore, the satellite images were used for structural analysis of the Izeh fault. The study area lies between latitude 31° 30  to 31° 52  N, and longitude 49° 30  to 49° 53  E. The geological setting of the area is just between the Izeh Zone and the Dezful Embayment. It has rugged topography and elevation ranged between 548 m to 1499 m (from sea level). Materials and MethodsIn this research, the ASTER image (with high spectral resolution), IRS-PAN images (with high spatial resolution), and Tectonic & Geological maps covering the study area have been used for structural analysis of the Izeh fault system. Furthermore, in order to 3D analysis of geological structures in the area, a detailed Digital Elevation Model (DEM) has been constructed, using digital Topographical maps (with scale 1:25,000). Geometrical correction and digital image processing techniques have been carried out by ER Mapped 6.4 software. The enhancing techniques (e.g. Data Fusion, Spatial Filtering, etc.) were applied for modification satellite images to highlight structural elements and deformational features of the Izeh fault. Moreover, the Sun angle (Directional) filters were applied for increasing geometrical parameters of structural lineaments (e.g. fracture traces) on the images. Also, to increase structural contrast on the DEM and improving visual description of fracture edges, Color dropped images and Shadow images (i.e. 2D DEM) of the area have been prepared. As well, by overlaying the DEM with satellite images and geological maps, 3D Models of the area have been constructed. Then, based on these models, the deformation geometries of the rock units were interpreted and mapped precisely. At last, in order to produce the digital Fracture Trace Map of the study area, all the acquired fracture traces data were integrated in Geographic Information System (GIS) environment by using ArcView 3.2a software. Results and DiscussionRS observations show that morphotectonic of the central Zagros has been modified by the Izeh fault system. Throughout the study area, a few Asmari formation outcrops (e.g. in Kamar-Deraz, Tanowsh, and Tukak anticlines) have been dragged and rotated in a way which is implied on right-lateral displacement of the Izeh fault. Moreover, the movements of the Izeh fault system had been associated with rupturing and/ or displacement of the Fars group (Mio-Pliocene) and the Bakhtiari formation (Pleistocene), too.The Fracture Trace Map of the study area is suggested that the Izeh fault had a great force on fracturing. For investigating about the Izeh fault effects on fracture patterns of geological units, the study area has been divided in 9 subzones. In each subzone, the structural data (e.g. azimuth, length) of the fracture traces were taken from the Fracture Trace Map. This can be done by using Distance/ Azimuth Tools v. 1.6 extension of ArcView 3.2a software. Then, in order to clarify the main fracture trends in each subzone, the Rose Diagrams of orientation data of fracture traces were calculated and plotted by using Rockworks 2006 software. In this matter, to compare the relationships between Number and Length of fracture sets, rose diagrams of orientation data have been plotted based on both Frequency and Cumulative length of fractures.The structural analysis of the fracture trace data are shown several fracture systems with varied lengths and orientations. The rose diagram plots indicated that fracture distributions in different subzones were not the same. Generally, throughout the area there are two main fracture sets (NW-SE and NE-SW trending) which are comparable to fold-related fracture system. However, in each subzone, there are few fracture sets which seem to be independent from folding. These fracture sets usually crossed through rocks with different ages and/or structural settings. Structural evidences suggested that these sets were related to reactivation of the Izeh fault during the Zagros orogeny. ConclusionThe RS observations and surveys in the Central Zagros show that the Izeh fault system is associated with complexity in the structural styles of the deformed rocks. The modification of geological units - with different ages and/ or structural settings - had been occurred through an extensive zone. From a morphotectonic point of view, the Izeh fault zone has been marked by right-lateral dragging and rotation of fold axes, and rupturing and/ or displacement of sedimentary strata, too. Moreover, the Izeh fault movements had been modified fracture patterns of the geological units. Throughout the study area, there are main fracture sets which had been associated with many subsidiary fracture sets. Structural analysis of the fractures suggests that some fracture sets are independent from folding mechanisms, and are related to reactivation of the Izeh fault during the orogeny.Consequently, morphotectonic and structural evidences are shown that throughout the Izeh fault zone, there are many structural features which have been created by different mechanisms, along with different stages of the Zagros orogeny. Furthermore, some evidences implied that this fault has been reactivated during juvenile phases of the alpine orogeny.

IntroductionDendrogeomorphology, which was first introduced by Alestalo (1971), is a subdiscipline of dendrochronology that, based on the analysis of annual tree rings and their growth morphology, addresses the spatial and temporal aspects of earth surface processes in Holocene period. The applications of dendrogeomorphology is dating and determining changes of various geomorphic processes such as floods, glaciers, storms, river channel migrations, mass wasting, earthquakes, volcanism and soil erosions, etc. Dendrogeomorphological research has mainly concentrated on tree trunks. Only to a lesser extent, roots have been studied for evaluation of sheet erosion rate and gully erosion. Estimating the rates of erosion based on the exposure of roots is based upon the changes in the wood anatomical pattern which occurs as soon as a root is exposed. Materials and MethodsThe study area is located in southern part of Gharachay catchment in Ramian County (Golestan province, Iran), between 36ْ 48ََ to 36ْ 57 N lattitude and 55ْ 6ََ to 55ْ 17 W longitude. Gharachay catchment drains an area of 143 km2. The altitudinal extend of the area ranges from 560 m in the northwest to 2650 m in the southwest. Geologically the studied area is a part of the Gorgan-Rasht zone in the Alborz mountains. The geological formation of this area includes Khosh Yeylagh (Kh), Lower part of Khosh Yeylagh (LKh), Mobarak formation (Cm1), Ghezel Ghaleh formation (Gh), Doroud formation (D), Lower Shemshak (Js1), Middle Shemshak (Js2), Upper Shemshak (Js3), and Old Alluvial Fans (Qt1). The aim of this research is a dendrogeomorphological analysis of tree roots for estimating the rate of sheet erosion in Gharechai (Ramian) Catchment. At first, DEM, slope and aspect map of the study area have been generated based on the topographic map at a scale of 1:50000 from Iranian National Geography Organization toposheets. Lithological formations were derived from the Geologic map of the studied area at a scale of 1:100000 by means of GIS (Integrated Land and Water Information System (ILWIS)). Before sampling of tree roots, the location of the exposed roots recognized by field observations and a detailed geomorphic mapping of the mentioned area. Before cutting each section, a detailed delineation of the spatial and morphological characteristics of the surroundings of the root-such as tree type, geographical location (UTM coordinates), altitude, aspect; slope of the specific root-was made. A total of 42 samples of tree roots from conifers and broadleaf species that were nearly and uniformly distributed in the catchment (Fig. 5) were obtained. Following detection of exposed roots, 38 sections of conifers (33 sections from yew, 1 section from cypress, 3 sections from juniper, and 1 section from pine) and 4 sections of broadleaves (2 sections from ash and 2 sections from oak) were provided during August 2008. During the cutting of tree root samples, sun-exposed part of outcropped root, contact of root and soil surface, the vertical distance between the upper part of the root and the present soil surface were measured for every section. Results and DiscussionIn this study, the height of eroded soil layer since the time of exposure (Er) has been calculated by Gartner method (2007, P. 248). Several parameters have been calculated for reconstruction of Er. At first, the exposed part (height) of the root (Ex) for samples was recorded. Reconstructing the first year of root exposure was carried out by analyzing the changes in the ring-growth pattern (from concentric to eccentric) and thereby the size of the root (excluding bark) at the time of exposure (R2) was determined. Then, the size -or height- of whole root (including bark) in cross section (R1), thickness of the upper (B1) and lower (B2) part of the bark were measured. Based upon the Gartner method (2007), Er has been calculated as follows: Er=R2+ (B1+B2) /2-R1+Ex (1) The value of Er was divided by the number of rings growing since the year of exposure (NRex) to calculate the annual erosion rate (Era): (2) Whereas conifers show more observable growth rings in comparison with broadleaves, most of the root cross sections of this study have been derived from conifers such as yew that have distinguishable growth rings. The mean sheet erosion of study area, based on sections of exposed tree roots, has been estimated 0. 541 mm/y. erosion rates in sections with 200-250, 150-200, 100-150, 50-100 and less than 50 years old are 0. 25, 0. 30, 0. 40, 0. 48 and 0. 86 mm/y respectively. ConclusionThis represents that the rate of erosion has been increased since the past 250 years. Analyzing the erosion rate in vegetation types reveals that the mean erosion rate is lower in denser forests than sparse forests. Evaluation of erosion rate in geological formation reveals that the mean erosion rate in soils over geological formations that have less dense forests, such as Lower Shemshak (Js1) and Middle Shemshak (Js2), is higher. This study also shows that conifers like Yew and Cypress that have more obvious and countable rings, have more capabilities in estimating erosion than broadleaf species like oak and ash.