Abstract:
دمای سطح زمین (Land Surface Temperatur) بهعنوان متغیر مهم ریز اقلیم و تشعشع انتقالی داخل جو، یکی از معیارهای مهم در برنامهریزی ناحیهای و منطقهای است؛ ازاینرو، عامل مهمی در کنترل فرایندهای زیستمحیطی، شیمیایی و فیزیکی زمین است. فعالیتهای طبیعی و انسانساز بهویژه نوع کاربری اراضی و پوشش زمین با تغییر شرایط فیزیکی و زیستی یک منطقه پارامتر مهمی در مقدار دمای سطح زمین است. در این پژوهش، تغییرات کاربری زمین و رابطه آن با دمای سطح زمین و شاخص پوشش گیاهی حوضه آبریز کیوی چای در سالهای 2019 و 1987 با استفاده از الگوریتم تککاناله روی مجموعه تصاویر لندست 5 و 8 بررسیشده است. رابطه بین کاربری زمین، دمای سطح زمین و شاخص پوشش گیاهی با استفاده از شاخص مشارکت (Contribution Index) و تجزیهوتحلیل همبستگی پیرسون ارزیابیشده است. بین سالهای 1987 - 2019، مساحت کشاورزی دیم از 390 کیلومترمربع به 217 کیلومترمربع، مرتع از 1224 کیلومترمربع به 1046 کیلومترمربع و آب از 11 کیلومترمربع به 3 کیلومترمربع کاهشیافته است، درحالیکه مساحت کشاورزی آبی از 137 کیلومترمربع به 388 کیلومترمربع، باغ از 10 کیلومترمربع به 60 کیلومترمربع، جنگل از 47 کیلومترمربع به 75 کیلومترمربع و مسکونی از 3 کیلومترمربع به 32 کیلومترمربع افزایشیافته است. میانگین دمای سطح زمین در حوضه آبریز گیوی چای 72/33 (1987) و 83/40 (2019) است. بیشترین مقدار دمای سطح مربوط به کاربری کشاورزی دیم و کمترین آن مربوط به کاربری جنگل و باغ است. بیشترین شاخص مشارکت در دمای سطح نیز مربوط به کاربری مرتع است. شاخص مشارکت کاربری مرتع از 4/1 در سال 1987 به 26/2 در سال 2019 افزایشیافته است. همچنین در دو دوره مطالعه بین دمای سطح زمین و شاخص پوشش گیاهی همبستگی منفی وجود داشته است.
Background and Objective Irregular and unplanned urban expansion is known as urban sprawl and is characterized by low-density, transport-driven development, spreading out over large swathes of land towards the fringes of established urban centers. It is generally held that morphological modification of the urban landscape results in rising urban temperatures and the urban heat island (UHI) phenomenon. The biophysical properties of the urban space are determinants of the local urban climate. When there is significant alteration such as the replacement of vegetation and evaporating surfaces with impervious surfaces, the surface energy budget experiences fluxes which leads to warming at the local scale. Most scientists believe that the Earth's temperature has been rising since the 19th century. Meanwhile, a phenomenon called heat island in metropolitan areas (UHI) has caused a faster rise in temperature in these micro-climates, and in the coming years, the rapid urbanization trend will also increase the slope of temperature rise in cities. According to statistics provided by the United Nations, by 2025, more than 80% of the world's population will live in cities, and this will worsen the situation as cities become warmer. Surface temperature (LST) is one of the most important environmental parameters that is affected by land use change. The purpose of this study is to analyze the land use change in the two periods of 1987 and 2019, to estimate and study the changes in LST and NDVI in the same period, and to analyze the impact of land use change in LST and NDVI and the relationship between all three parameters.Materials and Methods In this study, Landsat 8 satellite images were used from the OLI sensor to extract the land use map and vegetation index, and the TIRS sensor was used to extract ground surface temperature for 2019 also Landsat 5 OLI sensor image was used to prepare land use map and vegetation index. Using visible, near-infrared, and infrared bands, the TM sensor was used to extract the surface temperature using thermal bands for 1987. Ecognition software was used to classify the object. Error matrices and related statistics (overall accuracy, kappa coefficient, user and Producer accuracy of each class) were used to evaluate the classification accuracy. Finally, Pearson correlation analysis was used to analyze the correlation between LST and NDVI, and the Contribution index was used to evaluate the impact of land use on surface temperature.Results and Discussion Investigating land use changes and their relationship with land surface temperature and vegetation index requires determining the type of land use and accurate estimation of land surface temperature and vegetation index. Preparing a satisfied land use map using Landsat satellite images and applying the object classification method Oriented has a relatively high accuracy. The accuracy of land use map classification in 1987, 82.5, and in 2019, 96.1 shows the high accuracy of the land use classification method and land use map. The study of land use changes in 1987 and 2019 in the Givi Chay catchment showed that rangeland use with an area of 1224.18 and 10469.59 square kilometers is the dominant land use, while in 1987, residential use with an area of 66.63 square kilometers and in 2019, water use with an area of 3.77 square kilometers had the lowest area. Also, the most modified use of rangeland use was dryland agriculture (181 square kilometers), which indicates the destruction of rangelands. The results of surface temperature during the 33-year period were evaluated which showed that the average surface temperature in 1987 from 28.39 °C to 38.86 °C and in 2019 from 34.35 °C to 46.62. The temperature has increased so that the average temperature of the whole study area in 33 years has increased by about 7.11 degrees Celsius. This indicates the urban development in the study area. The highest temperature recorded in both periods belongs to dryland agricultural use (38.86 and 46.62 ° C, respectively), which indicates the concentration of heat in these areas. Dryness and harvest at this time can be the main cause of high temperatures of this use. Garden, forest, and water uses showed lower surface temperatures in both periods than other uses. Vegetation areas due to evapotranspiration have a temperature-moderating role and have areas with a minimum temperature in both periods. Water use also has a great effect on reducing the temperature due to its high heat capacity. The use of residential areas compared to rainfed and pasture agricultural uses showed a lower temperature, which can be due to the existence of parks, and gardens that cause evaporation and cooling of the city, as well as factors such as roofing, felt in The reflection of radiant energy has a great share. Rangeland use had high temperatures (36.57 and 44.81 °C, respectively) in both years under study. The reason for the high temperature of this land, according to the study season, which is late June and early July, is an increase in areas free of vegetation or vegetation that is small and scattered. There was also a large negative correlation between LST and NDVI in the two study periods. Rainfed and rangeland agriculture with higher LST have lower NDVI, while vegetation and water have higher NDVI. Aquatic agricultural use, which was mostly observed in the areas around the Givi Chai River, showed lower temperatures due to the presence of moisture and evapotranspiration due to vegetation density. In the study area, suburban areas (gardens) and irrigated arable lands along the Givi Chai River and forests have the highest amount of vegetation index (NDVI) due to their relatively high green biomass, while irrigated areas, rainfed lands, Residential areas, and pastures have the lowest vegetation index. The results of vegetation index analysis for each land use class showed that forests, rainfed agriculture, and rangelands with the highest LST values and the lowest NDVI values while the lowest LST values and higher NDVI values were observed in forest and garden classes. Replacement of vegetation and forests with residential areas causes the conversion of wet soils to impenetrable surfaces, which leads to reduced surface evaporation. Absorbed solar radiation is converted to heat and reflected with higher values of LST. Increased vegetation has reduced the earth's surface temperature, and this is due to the fact that more vegetation leads to more evapotranspiration and transfer of part of the temperature and cooling of the earth's surface. Finally, the calculation of the participation index for each land use class in 1987 and 2019 showed that dryland agricultural use in 1987 and rangeland use in 2019 had the largest share in increasing surface temperature in the study area. According to the time of the selected images, the main reason for this participation can also be attributed to the time of harvest of dryland agricultural products and drying of pastures.Conclusion The results confirm the increase in surface temperature between different land use classes. Rangeland and dry agricultural uses showed higher LST values compared to forests and irrigated agriculture and water areas. High-temperature areas also had low NDVI values. Conversely, low-temperature areas such as vegetation and water had higher NDVI values. In addition, a high negative correlation was observed between LST and NDVI in both study periods. It has also been shown that rangeland and irrigated agriculture have a positive effect on LST, while forests and water have a cooling or moderating effect.