فصلنامه پژوهش های جغرافیای طبیعی
پیاپی 69 (پاییز 1388)

This paper deals with the numerical tracking of Middle Eastern cyclones. Cyclogensis regions and their movement tracks can be determined by respective algoritms. In this paper, re-analyzed NCEP data with the temporal resolution of 24 hours and the spatial resolution of 2.5 2.5 degrees, were used for the cold period (December, January, February, and March), of the years 1993-94 to 2002-03. The area study is located at 10oN-45oN and the longitude 0oE-65oE. An algorithm written in C++ language was used for locating the points, and ArcGIS software was utilized for drawing the tracks. As a result, Five main tracks were characterized as most important tracks originated from western and northwestern areas; each month exhibits its own particular climatology. In January, the tracks tend to extend along the northern Mediterranean area. In March, the Atlantic low pressures increase noticeably. Most of the tracks have two-or three-day lifetimes; the effect of topography factor on formation of cyclogenesis regions is more outstanding than on leading the tracks. Cyclones which enter Iran are along three main tracks and three sub-tracks. The most important track is the one that enters from the west, originating from Cyprus region; the frequency of occurrence of cyclones exhibits an ascending trend.

Soil erosion by water is one of the most important processes of land degradation in arid and semi-arid regions of Iran. In this regard, gully erosion is a well-known process degradation which being controlled by verity of environmental conditions. The main aim of this research consist of assessing multi-parameter fingerprinting method to discriminate the sediment contributions of gully erosion through the combination of tracer properties (organic carbon OC, Nitrogen N), Phosphorous P, C/N and 137Cs) in three catchments. Results indicate that gully erosion is responsible between 86 and 99% of the catchments sediment. Due to same conditions of soil, lithology and climate different achieved contribution of gully erosion could be addressed to geomorphic parameters (e.g. area, drainage density, hillslope length and gully distribution). Generally, at a given gully density when the catchment area increase the hillslope length, which reduce the transportation of soil eroded on the hillslopes by sheet and rill, will increase and consequently gullies would deliver more sediment than hillslope processes. Further more, radionuclide 137Cs with the amount of residual root mean square error (RRMSE) (0.12%) was the most informative tracer properties to separate top-soil and gully sediment source. Finally results indicate that a gully erosion rate becomes notable from an area about 5 ha. The large influence of gully erosion, channel and river banks on sediment yields of watersheds implies that estimation of erosion rate by models such as: USLE, MUSLE, WEEP, EUROSEM, GUEST and runoff plot, which mainly focused on sheet and rill erosion, is not reliable and should be taken account by land managers.

Quantitative measurement of meteorological drought, Z score(z), rainfall anomaly (RAI), standard precipitation (SPI) indices and Percent of normal precipitation (PNPI) based upon seasonal and annual rainfall data of the 15 meteorological stations of meteorological in Hamedan Province were used. Also, in studying influences of drought on agriculture relative yield index of wheat was used. The results have shown that Z, RAI and SPI indices in seasonal and annual scales and PNPI in seasonal scale are good estimator of drought intensity and drought duration, irrespective of indices kind mostly was medium and lower than medium. Z, RAI and SPI indices were same with agronomic index of relative wheat yield, but SPI index based upon intensity of droughts had more similarity with agronomic index of relative wheat yield. The results show that Hamedan region have suffered from one drought which lasts from a two years lasting drought period in each decade. It has been also experienced a very severe drought during the last 30 years. Occurennce of more droughts in the region might be resulted from shortening the drought return periods, and increase of low intensity drought events in the region.

Massif of Parav-Bistoun covered around 880 square kilometers of the thrust zone of Zagros Mountains and located in Kermanshah province. There are various kinds of karst Landforms such as jamas, uvulas', dolines, caves in this mountainous area. These landforms are under the influence of palaeoclimatic conditions. Nowadays, current climatic conditions in this area allows for development of karst landforms only in high altitudes, over 2500 meters. The rates of karst development are shown by correlation between precipitations and hydraulic coefficient, and also the rate of precipitations that influence the discharge of springs. Therefore, in this research, karst evolution in Parav-Bistoun massif has been evaluated based on hydrogeologic parameters. This work is based upon the Study of isotopic –chemical characters, Estimate of recession coefficient– volume of dynamic storage, Analysis and comparison between characteristics of major springs in Parav-Bistoun area, such as Sarab-Barnaj, Sarab-Bistoun, and Sarab-Tagh-e-Bostan, to other springs in the folded Zagros zone, such as Sarab-Shian and Sarab-Niloufar. In this research, our data for analysis belongs to the hydrological year of 1995. The result shows that the hydrograph of springs, that come out from karsic area, are more complicated. In fact the reason of low rate minerals in Tagh-e-Bostan spring are depended on the canalized recharge system and limited contact surface with the solution agent (water). High rate of tritium in the water of Parav-Bistoun massif springs, indicate their relations to characteristics of precipitation, rate of Carbon-14 and CO2 that indicated the rapid penetration of water through the karstified system and low level contact between water and bedrock and finally exist of canalized system in the study area. Evaluation of the rate of isotopic characters in springs, such as tritium, Carbon-14 and CO2 pressure show the karstified character of the area. Furthermore, death time of the springs, their recession coefficients and dynamic storage volume (in the Parave-Bistoon springs), implies high levels of karst development in the area and denote to conduit and canalized feeding system of the springs.

In this study, the quaternary deformation and tectonic activity of Saeedabad-chai drainage basin, are assessed using geomorphic approach. This drainage basin is located in northern slope of Sahand Mountain. North Tabriz Fault (NTF), is passing from the Saeedabad-chai basin. Variation in the morphology of mountain front provied the basis for geomorphic assessment of tectonic activity. Therefore, it is used from geomorphic Index as Stream Length Gradiant Index (SL), Asymmetry Factor (AF), Topographic Symmetry Factor (T), Drainage Basin ShapeRatio (Bs), Mountain Front Sinusity (Smf), Ratio of valley – floor with to vally height (Vf), Percentage undissected mountain factors (Eu), Topographical maps, Digital Elevatiom Model (DEM), satellite images and Autocad map, Arc/view software. The results of this study that estimated by Index of relative active tectonic (Iat), indicated that the value of tectonic activity in the Saeedabad-chai drainage basin, is high.

Land cover map is important for many urban planning and management activities. In this study, in order to produce land cover map of Arak city, digital image of LISS-III scanner acquired on 16 June 2006 were employed. First of all, geometric correction with RMSe 0.58 pixel was applied. Considering the mountainous condition of the study area, topographic correction was applied to the image. In support of image classification, two different methods namely, supervised classification with Maximum Likelihood classifier algorithm and a three-layer perceptron neural network with and without using slope map were used. Finally, land cover map of the study region was classified into four classes: urban areas, vegetated areas, barren lands, and rocks. In order to sort out the rocks precisely from other classes, classified slope map of the study area was introduce to neural network model as an input layer. To assess the classified land cover map precision, it was controlled for ground truths with a GPS and the overall accuracies were 92.6, 92.7 and 94.6% for maximum likelihood classification, neural network classifier with and without the usage of classified slope map, respectively. The results confirm that the neural network classifier is capable to generate land cover maps with high accuracy.

Modeling is important in understanding complex ecogeomorphological relationships for useful applications, include: predicting the likely success of remobilizing dormant dune systems, managing and mitigating desertification and degradation of semi-arid land, assessing the impact of climate change, investigating the effects of changes in land use and reconstructing conditions responsible for the formation and stabilization of relict systems. Nebkha dunes have been proposed as a reliable rapid indicator of Aeolian erosion and vegetation. The aim of this paper is understanding the relationships between nebkha morphometry parameters together and with morphological characteristic of Reaumeria turcestanica. For obtaining objective of study we measure canopy cover and height of plant and elevation, diameter and slop for nebkha from 10 transects and 157 samples in khairabad area in Sirjan. The technical method used for investigation of relations was simple and multivariate regression analysis. Regression analysis showed a significant relationship (<0.01) between plant height and nebkha elevation with coefficient of determination (R2) of 0.58 for linear relationship and 0.60 for both quadratic estimation. Also a significant relationship (<0.01) exists between canopy cover and nebkha elevation with coefficient of determination of 0.54 for linear function and 0.58 for both quadratic estimations. Analysis Regression significant relationship (<0.01) between nebkha height and nebkha diameter with R2 of 0.49 for linear and quadratic estimation and 0.50 for cubic function.

The aim of this research is investigating the relations between climatic large scale signals and spring rainfall of Khorasan-e Razavi province. In this research, we have analyzed 38 years of rainfall data in khorasan-e Razavi province, located in northeastern Iran. We attempted to train Artificial Neural Network based upon climatic large scale signals with 38 years of rainfall data. For performance evaluation, network predicted outputs were compared with the actual rainfall data. At the outset of this study, the relationships between synoptically pattern variations, including Sea Level Pressure (SLP), Sea Surface Temperature (SST), Sea Level Pressure Gradient (?SLP), Sea Surface Temperature Difference (?SST), Air Temperature at 700 hPa, Thickness between 500 and 1000 hPa level, Relative Humidity at 300 hPa and Precipitable water are investigated. In the second step, model was calibrated from 1970 to 1997. Finally, rainfall prediction is performed from 1998 to 2007. Simulation results reveal that Artificial Neural Network is promising and efficient. Root mean square was obtained 2.5 millimeters.