تغيير آب و هوا و مخاطرات آب و هوايي شهر تهران

Climate Change and Climate Hazards in Tehran

شهر تهران در جنوب كوههاي البرز، امروزه مواجه با سه نوع مخاطره آب و هوايي است، مخاطره آب و هوايي ناشي از جغرافيا، مخاطره آب و هوايي ناشي از پايداري هوا و مخاطره آب و هوايي ناشي از گرمايش جهاني. هدف از اين پژوهش مطالعه اين سه نوع مخاطره در شهر تهران است. روش كار در اين پژوهش بررسي روند تغييرات عوامل سينوپتيكي است كه تحت تأثير گرمايش جهاني و توسعه شهري دچار تغييراتي شده اند. بدين منظور ارتفاع ژئوپتانسيل تراز 500 هكتوپاسكال جهت تغييرات پر ارتفاع جنب حاره اي در دو بازه زماني 5 ساله، بازه اول از 1948 تا 1952 و بازه دوم از 2010 تا 2014، مورد بررسي قرار گرفت. نتايج نشان داد كه در بازه هاي زماني نزديك تغييراتي در ارتفاع ژئوپتانسيل تراز 500 ژئوپتانسيل رخ داده است كه باعث افزايش مخاطرات در شهر تهران شده است. بر اثر تغييرات آب وهوايي در دهه هاي اخير، پايداري هوا و دوره تسلط آن بر نيوار شهر تهران افزايش يافته است. پايداري هوا در تهران به دو گروه پايداري هاي حرارتي و پايداري هاي برودتي تقسيم مي شوند. عوامل انسان ساخت باعث تشكيل جزيره حرارتي، افزايش ارتفاع LCL شده و تراز تراكم هوا را به ارتفاع بالاتري انتقال داده است. تغيير ميدان باد شهري، تشديد توربولانس هاي جوي، تشديد گراديان هاي ترموديناميك، فربه اي سيكلون هاي مهاجر ، از اثرات جزيره حرارتي شهر هستند.

Tehran, in the south of Alborz Mountains, is faced with three types of weather risk, weather risk caused by geography, climatic risks caused by air resistance and weather risk due to global warming. The aim of this study is to examine the three types of risk in Tehran. The method of this study was to evaluate the changes of synoptic factors that affect global warming and urban development. In order to detect the height changes of 500 hPa two 5-year periods including 1948 to 1952 and 2010 to 2014, were studied. The results showed that changes in heights of 500 geopotential, there was an increased risk in the city of Tehran. The effect of climate change in recent decades, increased the stability of air in Tehran. Human factors in the formation of heat islands, increase LCL height and density of the air balance is transferred to a higher altitude. Changing urban wind field, atmospheric turbulence intensified, exacerbated thermodynamic gradient, fat and refugee cyclones, heat island effect of the city. thermal stability in the warm period will appear. The thermal stability of all levels of lower, middle and upper troposphere was intensified. Thermal stability couraged the development of subtropical high pressure in the area. With the arrival of the atmospheric pressure during calm and humid days the stability and pollution were increased. Negative vorticity from early June developed the intensive high pressure over the region. Compare the conditions of the two study periods showed that : the height of the high pressure was 100 meters higher than the second period. The number of days of intensified subtropical high increased during the second period. The high pressure has moved to the northern areas during the second period. This change in the subtropical high pressure increased the dry periods motivating the loss of vegetation. Heat island effect was increased as well. More than 90% of the temperature inversions occurred at an altitude of less than 500 meters in both warm and cold periods of year. Wind direction at both stations has shown that the establishment of any pollutant source in the West of Tehran will increase the pollution.