جستجوی مقالات مرتبط با کلیدواژه « spatial variations » در نشریات گروه « جغرافیا »

Changes in the hydrological response due to climatic parameters and human induced activities can be derived from indicators based on the analysis of flow duration curves. The purpose of this research is to determine the flood and the low flow parameters using the flow duration curves. The trend detection technique can be used as a useful tool in deterimining the temporal changes of the different hydro-meteorological parameters. The river gauge stations of the Ardabil province were used for the analysis of high and low flow occurrence in this study. The spatial variations of the flood events can be used as a preliminary guideline for the prioritization of the watershed in the vulnerability assessment and management-oriented measures. Also, the assessment of low flow condition is a useful tool in the allocation of environmental flow allocation and utilization of river surface water resources.

In this research, temporal and spatial changes of Q10, Q50, Q90, Q90/50 and Lane indices in 31 hydrometric stations of Ardabil province during the period from 1993- 2014 were evaluated. The flow duration curve of each river gauge stations was derived. The flow duration curves also were plotted based on the dimensionless flow divided by the mean discharge and the upstream area of each river gauge station. Also, the temporal variations of the of Q10, Q50, Q90, Q90/50 and Lane indices were analysed using non-parametric Man Kendall trend test. Then the significant level of upward and downward trend directions were determined. In this study, the results of 5 river gauge stations were presented as example based on the the river flow ranges, which includes low, medium and high river flow discharge (Hajahmadkandi, Nanakaran, Shamsabad, Polesoltani, and Booran).

Based on the results, the trend of Q10 (Flood flow index) was significant at the stations located on the main trunk of the Qarehsou river. Meanwhile the Q50 (average flow index) has a significant decreasing trend in most of the studied river gauge stations. In addition, Q90 and Q90/50 indices have a significant decreasing trend in most stations. In addition, Q90 and Q90/50 indices had a significant decrease at (p<0.05) regarding the Lane index as a flood related indicator in the Arbabkandi and Dostbeglo stations, which are affected by the dam construction there is a significant decreasing trend.

I summary, the values of flood flow index in the upstream rivers of the Ardabil province had a increasing trend.

The purpose of this study is to analysis monthly OLR of the Iranian surface. For this purpose, the ground OLR data was extracted and analyzed from the ncep/ncar database during the statistical period of 1354-1398. In order to extract the have been used in the Gards software and GIS. Findings showed that by examining the spatial index of Gi statistic, the hot spots of Iran's OLR are 99% and 95% in August, July, June, September and October. Hot spots correspond to areas of the tropics and to latitudes below 30 degrees north; Also, the maximum cold spots are at the level of 99%, 95% in February, December, January, March, April, and the maximum cold spots OLR from the northeast to the northwest. It includes the northeastern, northern and northwestern regions of the country, as well as the northern highlands of the Zagros Mountains.

During the last four decades, the rapid growth of urbanization has dramatically transformed many natural phenomena. Such changes led eventually to changes in the Earth's surface temperature. The purpose of this study was to investigate the relationship between land use changes and spatial variations of thermal islands in Mashhad from 1998 to 2016. Thus, land surface temperature and land use changes of Mashhad were extracted using Landsat satellite imagery (1998- 2016). The CA Markov model has also been used to simulate and predict the expansion of Mashhad. From 1998 to 2016, the constructed area, green space, rangeland and barren lands are changed from 138.52, 46.49, 35.85 and 100.71 square kilometers to 198.87, 29.98, 31.29 and 64.62 square kilometers, respectively. Thermal islands in terms of number and extent in 1998 were less extensive and less synchronous than in 2016. In 1998 the maximum level of temperature was between 42 to 48 degrees Celsius but it reached 46 to 52 in 2016. With respect to the expansion of constructed area in the mentioned time period, the thermal islands are moved from outside of the city to the inside and have been overlapped with hard and impenetrable planes. The obtained results from the prediction illustrate that the expansion of city will occur in northwestern sides more than the others and it will be less in southern sides due to the existence of altitudes.

 Strategic and important industries are established in areas with possible access to water. Industrial development requires abundant water. Analysis of environmental resources and their pollution is the first consequence of industrial and human activities. Therefore today, due to the large volume of discharge and pollution in the environment, direct use of water is neither reasonable nor possible. Discharging industrial wastewater in land could severely contaminate the groundwater. In oil pollution monitoring researches, it is noteworthy that pollution detection and renovation operations require time and economic costs. Contamination of Soil and groundwater with pollutants such as hydrocarbons and chemical solvents has various environmental impacts. In Iran, the concentration of pollutants in some groundwater resources has been reported to be up to three times more than the standard value. This indicates the effect of a large amount of waste in the area which decrease soil quality in a way that soil layers are not able to compensate for it. Therefore, wastewater changes the drainage of underground water resources. In Iran and many other countries, causes such as leakage from contaminated petroleum storage tanks, leakage from transferring lines due to worn pipes, transportation of oil products, etc. in oil extraction mines, and refineries results in groundwater and surrounding areas facing oil leakage.    The purpose of this research is to produce the water quality map of Shazand plain in Markazi province using Geographic Information System (GIS) technique and to investigate the effects of oil industries on the quality of underground waters. The first step is to identify areas affected by these oil industries and identified factors. Appropriate agricultural areas with water supply in the qualitative range were also identified. The location of existing wells in the plain, particularly wells located around the refinery and petrochemical complexes were investigated for the first time. Then, considering the direction of the water land in the plain and the paths of wells located at upstream mountains to downstream ordinary rivers, wells located in the refinery and petrochemical complexes were selected. Accordingly, 14 wells were sampled in the first stage and their coordinates were obtained using GPS. The samples were classified in the laboratory into four groups including physical parameters, chemical parameters, oil and water aromatic parameters and water volatile organic compounds parameters. In the next stage, the maps of water quality parameters zoning were prepared using the "Geostatistical Analyst" developer with the use of the interpolation method of "Inverse Distance Weighting (IDW)". Finally, spatial variations and the groundwater quality changes were investigated. Oil and aromatic parameters of water are presented along with the results of laboratory analysis in table 2. Results indicate that the numerical value of many parameters were less than 0.1 mg/L. Just two parameters (Anthracene and Pyrene) in well no.10 had a value of more than 0.1 mg/L. Yet, the total value of oil pollutant was quite different. In wells no. 3, 8, 9, and especially well no.10 the value was more than 0.1 mg/L. The zoning map and spatial variation trend, along with statistical-descriptive indexes of total petroleum hydrocarbon of wells were also produced. The spatial variation of oil pollutants in Dashte- Shazand wells in south-north direction showed an increasing trend, which gradually changed into a decreasing trend. A decreasing trend was also observed in west-east direction. Comparing descriptive-statistical indexes with the standard level, we concluded that the total oil pollutant parameter near well no.10, which is located in petrochemical complex faces contamination.  The present study sought to measure some important indexes of oil contamination in groundwater and surface water near Dasht-e Shazand refinery and petrochemical complex. Therefore, data were collected from 14 wells in the study area. Then, oil and aromatic products were analyzed in laboratory. Using geostatistical technique, spatial variations of quality parameters concentration were investigated and compared with the desired and standard level. Results indicate that most of the wells near Dashte- Shazand refinery and petrochemical complex do not show any sign of contamination. Yet, the concentration of Anthracene and Pyrene parameters in well no.10 is several times more than the standard level. This can increase the potential of contamination in Dashte- Shazand ground water resources. In wells no. 3, 8, 9, and especially in well no. 10, total petroleum hydrocarbon (TPH) was more than other wells. According to the TPH and PAH results, the contamination potential of well no.10 was quite large. Due to the development of Shazand refinery, ground water resources of the area face an increasing danger of contamination. Moreover, the area has a high potential of population increase in residential areas. Thus, water contamination can also endanger the local environment. This shows the necessity of an appropriate management plan and regular monitoring of ground water, surface water, soil and air in the area.  

The aim of this research is an analysis of tempo-spatial variations of Cloud cover at Iran. To achieve the goal, Cloud Fraction parameter has been used from cloud product of MODIS sensor on Terra satellite at level 2 and version 6 (MOD06) in the period of 2000 to 2013. Given that, the Available parameters in level 2 MODIS cloud products have not geographical coordinate’s regular network, At first, the Cloud Fraction parameter data were transferred to a regular network, due to this process, Climate analysis on the data is possible, Base on new database the results showed that In annual scale, the trend variations in cloud cover increase at a rate of 0.02% per annual (2% per century) in the country. Cloud cover in the seasonal scale showed that the decreasing trend occurs in autumn and increasing trend in other seasons. Cloud cover in the monthly scale, in July, October, December, and January decreased and there is an increasing trend in other months. The spatial distribution of cloud cover in the long-term annual trend showed that there is decreasing trend in the North East, North West and sporadically in the central regions and an increasing trend in the South, Southeast, and East of the country. Spatial distribution of seasonal trend showed that most parts of the country have been with the positive trend in autumn and the negative trend in winter.

The aim of this paper is assessing the theory of the erg stabilization in space and area. Accordingly, the study areas concluded all of the Ergs in Iran which have been evaluated using Landsat satellite images and remote sensing techniques. We have compared the area and borders of ergs for duration of 1973 to 2016.the results show that Ergs did not have any significant displacement during the study period. They are stabilized, with an area of over 35906 square kilometers in 1973 and so they have retained in their initial dimensions for 2016 (35173.5 km2).based on our analysis, the formation and transformation of Ergs are controlled by local winds which they mostly are the prevailing phenomena during the warm seasons . There are no local winds in the winters and ERGS spend a colder, wetter and quiescence duration. However the ergs not only have been stable during the study period but also our results revealed an expansion in salt land and playa surfaces around the ergs from 1973 to 2016. In addition, We found out no significant changes in the morphology of the edges Ergs. The study of subtraction of 19 large Ergs in Iran specified that more than 68% of Ergs spread on wet salt land and dry desert surfaces, 11% on the platform masses (Rige Lut and Gen), and 21% on other areas such as alluvial plains. Also results show that for preventing damage to the sand dunes dynamic, it is necessary to control the active Barchan in the transport routes.

The MODIS facility for the Earth Observing System is a key element that supports ambitious goals related to studying the Earth as a system. One of the MODIS products is high quality land surface temperature data that product in Terra and Aqua platforms. Knowledge of the LST provides information on the temporal and spatial variations of the surface equilibrium state and is of fundamental importance in many applications. Therefore it is required for a wide variety of climatic, hydrological, ecological, and biogeochemical studies. Due to the intrinsic scanning characteristics of the MODIS instrument onboard the polar-orbiting satellites, the differences in local solar time for pixels along a given scan line on the same day or for the same pixel on different days in one revisit period may reach up to 2 hour. As LST changes with local solar time, it is therefore not possible to directly compare the LST of different pixels on the same day or of the same pixel on different days. Awareness about slope of land surface temperature is an important factor for cognition of land surface temperature behavior that can be used for increasing spatial and temporal resolution, comparability with other data, and accuracy achievement. The results will help to calculate a time consistent land surface temperature.
Land surface temperature data used in this researchare product using Normalized split windows algorithm. This data downloaded from MODIS website (http://reverb.echo.nasa.gov/reverb) in daily time scale for temporal range of 2002/07/08–2015/11/30. Prior to this date Aqua MODIS data is not available. This dataset contain measurements of land surface temperature, quality assurance, view time, view angel, land surface emissivity and is available for day time and night time. MODIS Terra 10:30AM and Aqua 1:30PM data used in this study. A matrix in dimensions of 4984*1884077 is provided from this dataset for Terra and Aqua day time land surface temperature and day view time thatprovidedbasic information for this study. The slope of land surface temperature between tow observation of Terra (10:30AM) and Aqua (1:30PM) is calculated. View time and land surface temperature measurements should first recall and calculate variation of land surface temperature in relation to observationtime distance between Terra/Aquameasurement for each pixel of Iran for every day of time series.Slope of land surface temperature calculated inmonthly long term meanfor spatial and temporal analysis.
View time is an important parameter in analysis of land surface temperature slope. View time distribution of land surface temperature in Iran show that Terra and Aqua view time has a high uniformity in frequency percent of observation times for land surface temperature at 10-12 and 12:30-14:30 for Terra and Aqua respectively. The coordination of land surface temperature slope and topography inIran is high. Low elevation lands between Zagros and central mountain ranges with northwest to southeast direction and central hollows such as Kavir plain, Lut desert and Jazmouryan is visible with higher slope in land surface temperature in alldifferent months of year. North and south shorelines and high elevations is the regions with smaller slope of land surface temperature. The slopes of less than 2 kelvin/hourin land surface temperature occurred in 85% of Iran territory. Difference between Terra and Aqua land surface temperature decreased clockwise from northeast aspects to southwest and increased from northwest to northeast.Slope of land surface temperature has an inverse relation with slope of land and decreased one kelvin/hour from zero to 22 degree slopes.
Significant spatial and temporal variation that occurred in land surface temperature slope of Iran is the result of variation in environmental conditions and incoming solar radiation. Slope of land surface temperature in shorelines and mountainous regions is lower than deserts and low level elevations in all months of year. Slopes of zero to 1 and to kelvin/hour in land surface temperature covered great areas of Iran in different months. Zero to -1 kelvin/hour slope spread in winter season in high level elevations of Alborz and Zagros mountains. Decreasing of land surface temperature slope with increasing land slop can reflect relation between land surface temperature and elevation. The results show that small amounts of land surface temperature slop is the characteristic of major parts of Iran. In these conditions we can product a time consistent land surface temperature data for each pixels of every day in available time series for a time between MODIS Terra and Aqua observations.

Soil temperature and its changes both in space and time is one of the most important factors that not only affect matter and energy transfer in soil but also influence the direction and amount of all physical processes in soil. Soil temperature depends on several factors including topography, sun radiation, air temperature, amount of soil moisture, the thermal properties such as heat capacity, coefficient of thermal conduction and specific heat. By the advent of satellite measurements in the last decades, there have been some studies focusing on the use and validation of remote sensing measurement of land surface temperature data mainly MODIS products. MODIS land surface data have been validated over different land types like lake (Want et al., 2002; Hook et al., 2004; Wan, 2008) and rice (Want et al., 2004; Galve et al., 2007).
In this research, the land surface temperature data of MODIS Terra in the spatial resolution of 1×1 km was exploited from NASA web site. These kinds of data are available in sinusoidal projection system. To investigate the role of elevation on land surface temperature, the digital elevation model (Dem) of the region was also obtained from NASA web site. Terra data are available from the year 2000 to 2015. These data are available in hdf format. As the first step only the pixels that felled into the Zayanderoud River Basin were selected from the data. This extraction was done using the inpolygon function in Matlab. By applying this function in Matlab there were exactly 48347 pixels that were the corner stone of our judgment about land surface temperature. In the second step, the daily matrix of temperature was constructed for each calendar day and based on the daily time series of the seasonal data were based on the daily data. Then, we calculated the rate of trend over each of the pixels for each season by applying regression equation on each of the 48347 pixels.
Analysis of trend in land surface temperature for each of the seasons indicated that there has been trend whether positive or negative in each of the seasons. The examination of trend for the season of spring showed that most of the territories of the Basin have experienced a negative trend but in central parts of the Basin a very marked positive trend dominates this region. The investigations for the summer season indicated that in many parts of the Basin negative trend has occurred but in the central parts of the Basin a distinguished positive trend can be seen. The analysis for the fall season showed that in this time many parts of the Basin like the other seasons have had a downward trend in the land surface temperature. But similar to the other seasons, central parts of the Basin have experienced a positive trend. The analysis for the winter season showed that in this period the areas that have had negative trend are less than the areas that have had positive trend in extent. The surprising note about this season is that there is a positive and direct relation between the rate of trend and elevation. Greater is the elevations, the greater the rate of trend. This means that in this season the highlands of the western parts of the Basin that are basically regarded as the valuable source for keeping snow covers and snow glaciers can’t have snow covers like before, due to the dominating positive trend occurring in these regions.
In this study, the daily time series of MODIS Terra was applied to explore the spatial trend of land surface temperature over Zayanderoud River Basin. The smallest resolution of 1×1 km of these data was used to get a better picture of the trend. As the first step, only the pixels that fell into the natural border of the Basin were extracted by using Matlab functions. In the next step, the daily values of land surface temperature were aggregated to monthly and seasonal time scales. The analysis of the trend for each of the seasons indicated that in all of the seasons positive and negative trends have occurred but in general negative trend has had a greater domination. In the spring season only central parts of the basin has represented a positive trend but in the other parts decreasing trend prevailed. In the summer and fall like spring only the central parts of the Basin have had a positive trend. But in the winter the highland of western parts of the Basin has had a very marked positive trend that can be hazardous for this region due to this fact that these mountainous regions of the Basin is regarded as the source of snow cover of the Basin.