فصلنامه تحقیقات جغرافیایی
سال بیست و ششم شماره 3 (پیاپی 102، پاییز 1390)

Because of the passing of the air systems، temperature changes are often very sudden and plants cannot adapt themselves to these fluctuations and get damage. Because low temperatures have harmful effects on the agricultural productions، so، the investigation of these temperatures are very useful for predicting and preventing probable damages. In this study، for determining the time of the freezes occurrence، daily minimum temperatures of Tabriz station were used for a 21-year period. The longest and extreme freezes، occurred during 7-12 Farvardin 1382 (March 27- April 1، 2003) and 17 Farvardin 1383 (April 5، 2004). Synoptic maps in 1000، 850، 500 hpa were also used for detecting the synoptic patterns over these periods. The results showed that، the power and location of the pressure systems that prevail over the area during the freeze events were the main factors that control the freezes. Formation of low pressures and related troughs also have an important role in the spring freezes in area، and the main synoptic pattern that make the freezes is deepening the troughs of northern Caspian sea.

The criteria and standards of green space development should be specified before any planning for green space development. The cities'' conditions not only rule the creation of vast and more importantly planned and organized green spaces but also demand vast green space in order to establish ecological balance against made environments. This research tries to study green space per capita in region 12 of Tehran with regard to green space criteria determined، such as the local climate characteristics، environment quality and density of people in room in resident units. Then، considering these criteria، the green space per capita in region 12 of Tehran was specified. Green space per capita for each person is 5. 12 m2 in region12، which considering the above criteria should be increased to 35 m2 for each one. It is concluded that the maximum amount of 12 m2 for each person، which was proposed by Ministry of Housing and Urban Development for all cities، is not logical and per capita of each city should be calculated with criteria and environment condition of the city.

The air temperature trend has been increasing during recent decades، especially in the regions such as Iran which is located in dry and semi-dry world belt. In this research we used Markov chain to obtain probabilities of heat waves with different continues in Kerman province using 20 years daily maximum air temperature data during 1986-2005. We analyzed daily maximum air temperature data of 5 synoptic stations that had at least 20 years daily data. To obtain a statistical index for determination of heat wave events in every station، the days in which the maximum temperature exceeds from this index were defined as heat weave event. After determining heat events، we classified the heat waves to short and long heat waves events and the statistical trends of these events were calculated separately. Finally، the return period and continuation period of these events were determined and analyzed using Markov chain. Maximum temperature trend analysis in the Province Kerman indicated that most heat waves occurred in April and May، that this change has been an increasing trend during the period have been statistically، especially in 2000 reached its maximum height and then again the previous trend is growing. Finally، we estimated the probabilities of occurrence of 1 to 9-day heat waves in all studied stations.

The space structure that governs cities has depended on several corresponding relations and various factors which consist of: population، job and activities، transportation patterns، urban sub-structures، various services and etc that always were connected to each other and have formed its space structure. But since these relations are more complicated in big cities، the importance of paying attention to their space structure becomes more important. Nowadays، civilization has turned to an important and complicated problem in various societies and is growing fast in recent period of ten days –especially in metropolitans it has caused several anatomic، economic and social problems. The fast spreading of cities have caused a number of problems such as emigration and slum، city order distribution، traffic and implication of environment، which must be carefully studied. Small cities have just one center or one central core but nowadays big cities particularly metropolitans have several centers that according to economic، anatomic and connecting foundation factors centrals and different fireplace living have formed not so far from historical and central centers of the town. These cores have been created according to their position near the railway and transport direction، airports، industrials centers، universities and sporting (fun) center، etc. and follow that one centrality or a new urban center have developed and with spreading connection lines and completing that، the town has become polycentral. Such space structure of cities depends on factors such as expanding industries، distributing economic institutions، expert and various activities، amount of rent، agent of cars، communication lines and the special earning of socio-economic، etc. The purpose of this research is to present polycentric space structure of urban and metropolitans and analyze and organize the space that was achieved by having a case study of Karaj. In this research، using peter halls polycentric model and analyzing Karaj city structure within this model، we achieved the space planning and appropriate strategies in this city.

In this investigation، using Mann – Kendall graphical-statistical test، which is one of the proposed methods of World Meteorological Organization (WMO) for time series analysis، the change trend of long – term mean of annual minimum and maximum temperatures in Iran will be studied. To evaluate this trend and access a suitable pattern in this situation، average of annual minimum and maximum temperatures from 44 synoptic stations for a 40 year period (1969-2008) has been collected from the Meteorological Organization of Iran. Results of the study show that most area of Iran has witnessed both types of changes: maximum temperatures average and minimum temperatures average. However، these changes have not been of the same form and amount in most area of Iran. 28 stations which were in west، northwest، southwest، northeast and centre of Iran have had increasing in annual maximum temperatures average، all of which have been significant in. From among residue stations only two stations of Chabahar and Torbate Heydarieh have had decreasing changes and in other stations no changes were observed. These occurred changes in all stations were all from abrupt changes type. From the viewpoint of time، the most centralization of start time of changes is seen in the third decade (1989-1998). From among 33 stations that have had increasing in annual minimum temperatures average، 19 stations have possessed changes from trend kind and remainder of stations had abrupt changes. These increasing changes have been seen in most area of Iran except small parts of west، southwest، south and one station in east of Iran. Two stations of Fassa and Shahre Kurd have had decreasing trend in annual minimum temperature average and in remainder stations no trend or changes were observed. From the viewpoint of time، the most centralization of start time of changes is seen in the third decade (1989-1998). The arithmetic mean of Mann-Kendall test statistics was found to be 0. 24 for maximum temperatures and 0. 4 for minimum temperatures، which indicate double changes in minimum temperatures compared with maximum temperatures average.

Urban development in the country as a whole and in Tehran in particular has become inconsistent due to spatial reflection of informal settlements. This problem can neither be left alone to itself nor can it be solved through a segmental، selective and scattered approach. The formation of informal settlements is an evidence for the presence of structural obstacles as well as the inefficiency of current housing policies and related services for the urban low income group in the large scale. On the lower scale also، weak urban management، existence of unofficial interest sources and influential local groups، and the unsystematic approaches towards the acceptance or rejection of such settlements have all intensified the problem. Therefore، if we are to solve the problems of this type of settlements، a careful and precise planning for improvement and empowerment is deemed necessary. Baghershahr in the southern part of Tehran is one of these informal settlements which under the influence of the country''s economical-social system and that of metropolitan Tehran، has witnessed major physical changes particularly since 1350s onward. What this article seeks to consider is an understanding of the formation process and the social-economical and physical characteristics of Baghershahr informal settlement as a whole and «Baba Jafari» Neighborhood as a part and also to provide a program for its improvement and empowerment.

A considerable part of precipitation falls in the form of snow in Golestan watershed. In turn، snowmelt plays a significant role in surface runoff، groundwater feeding and flood propagation in this area. Snow Cover Area (SCA) as an indicator of stored water can be implemented for temporal and spatial monitoring of snowmelt in the hydrological models. To monitor spatial and temporal variation of snow cover area in Golestan watershed، snow product of MODIS satellite data (MOD10A2) in 9-year steps were retrieved for the period of 2000 to 2008. In addition، satellite products of Land Surface Temperature (LST) (MOD11A) were also acquired on corresponding dates. Using long term LST and SCA data، and a threshold method، areas with high probability of snowfall were classified. The results indicated that high temporal and spatial resolution MODIS satellite data has a high potential in the mapping of snow covered area.

Different problems and pitfalls of large cities، such as the inflation of land and housing، spiritual pressures، mental stresses، high degree of air pollution، as inhibiting factors in contrast to land and housing low-pricing tariffs، air cleanness، and the lack of urban problems and etc. in rural areas، as the attracting factors، automatically cause the dwellers to establish in those areas as well. Sometimes، the severity of this movement and population space displacement (reverse immigration) is such that some of these villages perform as dormitory villages with functional changes. The aim of this study is to investigate the reason of these changes and the relocation between Tabriz metropolis and dormitory villages as well as the factors influencing it. It is hypothesized that there are other factors related to this process such as facilities and closeness to a city، the possibility of providing a land and low prices in the rural areas، the type of the job and the occupation of immigrants. The current attempt is based on an applied descriptive-analysis case along with field operations (direct observation، using different questionnaires). The results of the study not only shows the closer relationship between Tabriz metropolis and dormitory villages، but also confirmed the important effect of «providing the land and cheap housing» and «closeness to the workplace» in the formation of reverse immigration in comparison to other influential factors.

This article studies the effects of weather on road accidents in Saqqez - Sanandaj road. Saqqez- Sanandaj road’s length is 187 km and it is one of the main hazardous roads of the area. In this study، the distribution map of road accidents and the probability of accidents were prepared under every climatic condition (i. e.، snowy، frozen، rainy، foggy، and sunny). A database of road accidents occurred during 2006-2008 was added to the road layer. Frequency classification of accidents occurred in different parts of the area in different weather conditions was then accomplished to identify risky areas. Results indicated that accidents could be identified as snowy weather conditions in 53 to 87 km، 93 to 152 km as freezing condition’s in rainy weather the path of 48 to 71 km، in foggy weather that of 73 to 85 km، in 51 to 79 km and all weather conditions، and 75 to 168 km paths were the area of maximum accident frequency and dangerous parts. Finally، using risk accident map and also the importance index of each factor on the basis of frequency of accidents، the zoning map of low risk، medium risk، high risk and very high risk areas was drawn. Findings show that parallel to the increase of number of snowy and rainy days، the frequency، severity of damage، the death toll and injured number of road accidents were determined.

The first implementation of rural guide and improvement plans of Iran goes back to about 20 years ago. At this period of time، at least 20 thousands plans of this type have been studied and many of them have been implemented. But in spite of spending a lot of charges by government، and bearing many problems by peasants، there is a low satisfaction of these plans، and in fact there is no signal of a logical equilibrium between charges and consequences. This study tries to determine some of the most important variables that affect the success of studying and implementation guide plans by using correlation methods. Therefore، it has selected and investigated the rural guide projects which have been implemented in South Khorasan province as a sample. Analyzing the data reveals that variables of people participation in studying and implementation، rich studying and implementation groups، technical and scientific characteristic of plans، paying attention to environmental hazards، financial problems and management traits on succession have had the highest effects.