| چکیده انگلیسی مقاله |
Abstract
Introduction: Meadows as natural ecosystems play a major role in the sustainability of nature, but unfortunately in recent years have undergone severe changes. The meadows of Shahrekord, which have severely changed in recent years, in addition to providing forage for livestock, from the recreational and weather regulation point of view is valuable due to its proximity to the city. Considering the importance of meadows in natural resources and environment, there are few studies on the importance of this valuable ecosystems and preventing their destruction around the world. The plain of Shahrekord meadow is one of the meadows that is severely degraded and changed in term of land use and unfortunately neglected by people and authorities. The difference between ground temperature and air temperature in a region is due to changes in the type of land cover and its thermal capacity. In this study, considering the importance of this valuable ecosystem, its role in weather regulation and the mitigation of land surface temperature, has been studied and evaluated.
Materials and Methods: Due to the availability and quality of Landsat satellite images, the data of September of this satellite were used in this study. Geometric corrections were applied on all of the images of the study area which were located in the 39N zone of UTM coordinate system (WGS1984). After the atmospheric correction, Shahrekord plain was clipped from the studied images. Then the training samples were selected for each land use/cover and finally classification was done using maximum likelihood algorithm in TerrSet software. The accuracy of the resulted Land use/cover maps were also evaluated using test samples taken from the study area via error matrix. After preparing land use/covers (LULC) map, the land surface temperature (LST) map were also determined from thermal bands of 6, 6-1, and 10, of Landsat TM5, ETM+7, OIL/TIRS-8 respectively, using temperature emissivity separation (TES) algorithm. In this research, the normalized vegetation index (NDVI) was also calculated using infrared and red bands of the Landsat images. Finally, the variation of ground temperature in relation to vegetation changes of Shahrekord’s meadows and its effects on temperature changes was evaluated.
Results and Discussion: In the present study, 5 sets of Landsat images were used for estimating land use/cover changes during 1987 to 2016. Kappa coefficient was used to verify the accuracy of the land cover maps. The results indicate anthropogenic changes in the meadows of Shahrekord. By comparing NDVI indices and surface temperature over a period of 29 years (1987 to 2016), it was determined that with urban development, surface temperature increased by 9.18 degrees Celsius (from 33.24 to 42.42 degrees of Celsius). The results showed that the correlation of the NDVI index with the surface temperature map was negative. Also, NDVI index have a more meaningful relationship with LST in meadow lands than in urban and bare lands. The maximum temperature change of the land surface was observed in meadowlands during 1987 to 2016. The highest temperature in 1987, when the entire area is covered with meadowlands, is 39.68°C, but in 2016 it is raised up to 45.51°C, indicating impact of meadowland’s regulation of temperature capacity. Regarding the land use change in ShahreKord meadowlands, as well as the results of land surface temperature in different classes of land covers, it shows that the temperature changes over the years caused by meadowland changes. Considering that in 1987 the average surface temperature of the meadowland was 39.68°C but in 2016 it reached to 45.51°C which caused an increase of 5.83°C reveals the importance of these lands in adjusting land surface temperature. A large change in these lands and the conversion of meadowlands into bare lands can be considered as one of the reasons for the change in the LST, most of which could be due to anthropogenic effects.
Conclusion: The regression line between the temperature of at ground meteorological station and the retrieved land surface temperature of 5 images extracted from the satellite images showed a coefficient of determination of 0.63 between 1994-2016. The results show that the lesser the amount of meadowland, the greater the correlation between surface temperature and air temperature. As the coefficient of determination of regression line between retrieved LST of images of 2001 to 2016 with the recorded temperature of meteorological station reached to 0.86, which shows a greater correlation. The results showed that based on the regression line between the retrieved temperature of the images and air temperature of the years 1994-2016 (regardless of the year 1987), the temperature of the 1987 year (when the condition of the meadows of Shahrekord was in a good condition) should be 40.93°C (with R =0.69), while the temperature was 32.24°C. In other words, it is 8.69°C less than the expected temperature. The difference between these two values is due to adjustability of the meadows, which in the recent years this change has led to an increase in temperature. This indicates the importance of the meadows in adjusting the LST, which is probably due to the amount of moisture and the level of groundwater table of the meadows. Therefore, it is recommended that we should strive to maintain this valuable ecosystem, which plays an important role in regulating the LST. |
