نوع مقاله : مقاله پژوهشی
1 دانشجوی کارشناسی ارشد اقلیم شناسی محیطی دانشگاه یزد، یزد، ایران
2 دانشیار اقلیم شناسی گروه جغرافیا دانشگاه یزد، یزد، ایران
3 دانشجوی کارشناسی ارشد مخاطرات محیطی دانشگاه یزد، یزد، ایران
پدیده جزیره حرارتی شهری، از معمولترین پدیدههای شهری است که طیّ آن برخی از نقاط شهری بهخصوص مرکز شهرها چند درجه از مناطق اطرافشان گرمتر میشوند. هدف این پژوهش، ارزیابی روند تغییرات دما، تغییرات جزیره حرارتی و پوشش گیاهی دوره گرم سال در شهر یزد می باشد. برای بررسی روند تغییرات دمای ماه های گرم سال، از اطلاعات دمایی ایستگاه یزد و آزمون من-کندال استفاده شد. به منظور تعیین جزیره گرمایی شهر یزد در ماههای گرم سال، از تصاویر ماهوارهای لندست 4-8 در محدوده زمانی33 ساله(2020-1987) که شامل چهار دوره با فاصله زمانی 11 ساله است (میانگین ماه های تیر، مرداد و شهریور سال های 1987، 1998، 2009 و 2020) استفاده شد. نتایج حاصل از تصاویر ماهواره ای نشان داد که در طی دوره آماری هر چه به سالهای جاری نزدیکتر شویم از میزان پوشش گیاهی و زمینهای بایر کاسته شده و در عوض به وسعت ناحیهی شهری افزوده شده است. نقشه های LST نیز نشان از دماهای بالای 50 درجه سانتیگراد به صورت خوشه های داغ در قسمت های غرب و جنوب غرب شهر یزد بوده که در دهه های اخیر ایجاد و تقویت شده اند. آزمون من-کندال و شیب سنس نیز حاکی از روند صعودی معنی دار در سطح اطمینان 99 درصد به خصوص در سال های اخیر است. میزان این افزایش دما دریک دوره 45 ساله حدود 2.3 درجه سانتی گراد بوده است که این شرایط می تواند در پیوند احتمالی با پدیده روند افزایش جمعیت شهری طی دهه های اخیر و به دنبال آن افزایش سازه های شهری(مسکونی، تجاری) و پدیده جزیره حرارتی مرتبط باشد.
عنوان مقاله [English]
Evaluation of the Trend of Temperature Changes, Heat Island and Vegetation Cover During Hot Days of the Year in Yazd
- Foroogh Mohammadi Ravari 1
- Ahmad Mazidi 2
- Zahra Behzadi shahrbabak 3
1 Master student of Environmental Climatology, Yazd University, Yazd, Iran
2 Associate Professor of Climatology, Department of Geography, Yazd University, Yazd, Iran
3 Master student of Environmental Hazards, Yazd University, Yazd, Iran
The most important problems in urban areas are the increase in the temperature of the earth's surface due to the transformation of the natural surface, as a result of which the natural vegetation is removed and replaced by impermeable and impermeable surfaces) stone, cement, metal, etc.), this phenomenon is called the thermal island phenomenon, especially with the distinct and characteristic temperature difference between the city and the surrounding areas (Melkpour et al., 2018). One of the environmental problems is the increase of the land surface and heat islands in the areas that are turned into cities without prior planning or covering the surrounding lands. have been. As a result, it causes changes in land cover, which is well visible (Khakpour et al., 2016). The main reason for the occurrence of the heat island is the man-made surfaces, which prevent the reflection of sunlight and increase its absorption, and as a result, the temperature increases. In general, heat islands in cities cause an increase in air temperature, an increase in the temperature of the earth's surface and thermal inversion (Gartland, 2012).
The research method is statistical-analytical and its basis is the use of station data statistics and satellite images. In this regard, the climatic data of Yazd Meteorological Station from 1976 to 2020 have been used to measure temperature changes, and these data have been prepared and extracted from the General Meteorological Department of Yazd Province. Due to the fact that in urban climate studies, planning is based on long-term patterns, therefore, in this research, the common Man-Kendall method was used to measure the trend of changes in temperature parameters in the hot months of the year (July, August, September). Also, in order to extract the heat island of Yazd city in the hot months of the year, from Landsat 4-8 satellite images in the time range of 33 years, which are four periods with a time interval of 11 years (the average months of July, August and September of 1987, 1998, 2009 and 2020) has been used. These images under clear weather conditions were downloaded from the United States Geological Survey website at http://glovis.usgs.gov/ and the WGS-1984 UTM image system. NDVI index was used to check the vegetation cover. The main land uses that were discussed in this research include barren land, urban area, vegetation and road, which were identified in ArcMap software with visual interpretation and using sampling in Google Earth and using the algorithm The maximum likelihood was extracted and analyzed for the classification process. Finally, by extracting LST from satellite images, the temperature of the earth's surface was compared with the temperature trend of Yazd city using the Mann-Kendall test.
Results & Discussion
The results show that in the summer season, because the vegetation cover is more complete than in the winter, there is a negative relationship between the vegetation cover and the temperature of the earth's surface, and with the decrease of the vegetation cover, the temperature of the earth's surface has increased and vice versa. The classification of satellite images of land use in Yazd city showed that the city has expanded a lot in the 33-year period and has grown significantly regardless of the season under investigation. So that the area of the built land class has increased significantly. On the other hand, the land with vegetation has a negative trend and has decreased. The thermal images of Yazd city after applying the LST ground surface temperature extraction algorithm showed that parts of the city from the northwest to the south of the city due to the presence of barren lands and also due to the lack of benefits from evaporation and transpiration cooling mechanisms have the high heat absorption capacity along with the low conduction capacity have formed the core of thermal islands. The results obtained from applying the Man-Kendall test show that there is a significant upward trend in the temperature value, especially in recent years, when the temperature increase is about 2.3 degrees Celsius. This condition can be related to the phenomenon of urban population increase in recent decades, followed by the increase of residential structures and the heat island phenomenon.
In general, the results of the land use classification of Yazd city showed that the city had a lot of physical expansion and significant growth. The examination of the physical development directions of Yazd city showed that the expansion of the city has taken place in all directions, that this expansion was first in the central parts and the northeast-southeast parts, and the northwest-southwest parts expanded later. The results of NDVI showed that the maximum of this index is in the central part of Yazd, corresponding to the areas with higher vegetation. Also, the uses of green space can be seen as spots in some areas of the city. The change in the color spectrum in the LST map indicates the relative change of the ambient temperature from one point to another, and the high and very high temperatures that are between 41.5 and 50 degrees determine the location of the heat islands on the temperature maps. Also, the areas with a deep red color and a temperature above 50 degrees have formed hot clusters that were formed or strengthened between 2009 and 2020 in the west and southwest of Yazd. The results of the trend showed that in 2020, according to the graph and satellite images, we have witnessed a sharp increase in temperature and the occurrence of a heat island in the city of Yazd. The trend of incremental changes in air temperature based on the Man-Kendall test through the temperature data of the Yazd Meteorological Station shows a significant upward trend in the temperature value, especially in recent years. This increase in temperature was about 2.3 degrees Celsius These conditions are related to the phenomenon of urban population growth in recent decades, followed by the increase of urban structures (residential-commercial) and the heat island phenomenon.
- Thermal island
- land surface temperature
- land use changes
- Yazd city