واکاوی تاثیرات تغییر کاربری اراضی بر پوشش گیاهی و دمای سطحی شهر و واکنش مدیران شهری به این روند (نمونه موردی: شهر مشهد)
آرشیو
چکیده
زمینه و هدف: شهرنشینی تحولات گسترده ای را زمینه سازی نموده و منجر به تغییرات قابل توجهی در کاربری و پوشش زمین شده است. کاهش اراضی زراعی حومه ها و حذف پوشش گیاهی به همراه افزایش دمای سطحی خاک، تنها بخشی از پیامدهای منفی توسعه شهری و ازدیاد مناطقی که به زیر ساخت و ساز شهری می روند، قلمداد می گردد. به همین منظور، این تحقیق با هدف بکارگیری سنجش از دور در بررسی پیامدهای تغییر کاربری اراضی در شهر مشهد انجام شده و به تعیین و مقایسه آثار منفی آن روی کاهش پوشش گیاهی و افزایش درجه حرارت انجام شد. بدین منظور، از تصاویر ماهواره لندست، سنجنده TM مربوط به سال 1979 و سنجنده ETM+ مربوط به سال 2009 و سنجنده های OLI و TIRS مربوط به سال2023 میلادی استفاده شده است.روش بررسی: بررسی تغییرات پوشش گیاهی، با شاخص پوشش گیاهی تفاضل نرمال شده (NDVI) انجام شده و کلاس های مختلف سرسبزی (بدون پوشش، ضعیف، متوسط و خوب) تعریف و در سه سال مذکور مورد مقایسه قرارگرفته است. در این مدت، مساحت وضعیت پوشش خوب از 3/8 درصد در 1987 به 2/5 درصد در 2023 رسیده است.یافته ها و نتیجه گیری: مقایسه تغییرات دمای سطحی به کمک باندهای حرارتی نشان داد که تخریب پوشش گیاهی، باغات و مزارع واقع در محدوده شهر مشهد و تغییر کاربری آن در طی 36 سال، منجر به افزایش نسبی دمای محیط شده و میزان حرارت از 7/24 به 8/33 درصد افزایش پیدا نموده است. با این وجود، به دلیل توسعه فضاهای سبز، روند تخریب در طی سال های اخیر کاهش یافته است.Analyzing the effects of land use change on vegetation and surface temperature of the city and the response of urban managers to this trend (Case study: Mashhad city)
IntroductionUrbanization has triggered massive development activities which led to significant changes in land use and land cover (LULC). Fundamentally, the changes in LULC have to be monitored to detect the presence of regional environmental changes and impacts. Reducing the suburban area of arable lands, destruction of vegetation, and increase of land surface temperature in urban areas, and the effects of rising temperatures are some negative consequences of urban development, building street and other malicious activities within cities. This research aims to use remote sensing to assess the consequences of destruction, and changes in land use in the city of Mashhad, was performed, and this project is trying to focus on determination and comparison of its negative effects on vegetation loss and increase of temperature and the response of city management to these changes.MethodologyThe methodological framework adopted in this study involved different analytical processes of Landsat imagery to examine the effects of the LULC changes on land surface temperature. Satellite images for 1979 from Landsat 5 Thematic Mapper (TM) and Landsat 8 Operational Land Imager and Thermal Infrared Sensor (OLI-TIRS) for 2009 and 2023 were obtain and were used to analyze the changes in LULC in Mashhad. All the images were selected based on the clarity of the images with less cloud coverage; moreover, the images were all captured in the month of May for thecorresponding years. In this study, Orthorectification of images for 1987 and 2009 and 2023 in this study area, which has a geographic coordinate system, was carried out by the ILWIS software capabilities, and by using affine method. Then, using resampling on bands related to 1987, their sizes were equal to the bands of 2009. Vegetation map of the study area, using satellite data and remote sensing techniques were developed. For this purpose, a vegetation index called Normalized Difference Vegetation Index or NDVI was used.Results and DiscussionThe results showed that Based on the classified the uneven distribution of LULC in Mashhad varied by year. The built-up areas expanded tremendously in almost every part of city within 36 years. This pattern was also associated with the loss of vegetation cover as the built-up category took over the green space on a large scale. However, the land use pattern in 2009 displayed an exceptional fluctuate trend of vegetation and built-up areas dispersion. From the map roughly, there was a conversion of built-up area into vegetation land from 1979 to 2009. But in 2023, it appeared plausible that the previous barren lands which was categorized as built-up areas had turned into green space for urban agriculture or urban park. Referring to the map, it was apparent that the largest transition of vegetation cover into built-up areas occurred from the central towards the north of Mashhad. In general land-use patterns can directly impact the generation of heat in the urban climate. The identification of NDVI and LST parameters could provide useful information regarding the environmental changes for sustainable urban development and management. Hence, it can be concluded that a relative increase in urban ambient air temperature in Mashhad, therefore, vegetation is changed, which can be regarded as the negative effect of land use change in this city; but due to the development of green spaces, the process of destruction has decreased in recent years.ConclusionConjointly, rapid urbanization in Mashhad city led to the occurrence of regional heating based on the increase in LST value. Therefore, sufficient allocation of vegetation and water body in the city is recommended as a measure to reduce urban heat generation. Of course, because the development of green space has reduced the speed of changes, proper and timely intervention prevents the situation from escalating. Of course, such interventions should take into account all national and local conditions. So the study further recommends that additional factors like other LULC indices, socioeconomic variables, and other factors could be considered in future studies to produce more sturdy conclusions regarding the surface climate impact study.
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