چکیده:
In recent decades, due to rapid urbanization and industrialization, significant changes have occurred in meteorological quantities and land use in large cities. The extent of these changes depends on many factors, including the amount of released energy, population, latitude, and air ventilation conditions. The most prominent effect of land use change in cities is the change in radiation budget due to greater absorption of solar energy by asphalt-covered surfaces. To investigate the effects of urban development and land use change on some meteorological quantities in the Tehran metropolis, a comparison between temperature and wind trends in Tehran and Varamin over a forty-year period was conducted. This comparison indicates an increasing trend in minimum temperatures in Tehran compared to Varamin. The rate of increase in the annual average minimum temperature in Tehran is four times that of Varamin(). The results obtained from studying the monthly average minimum temperature trends show that the increasing trend is not uniform across all months and decades. The highest increasing trend in the monthly average minimum temperature of Tehran and Varamin occurred in November at 0.116 and in February at 0.030, respectively. Calculating the difference between the last decade of the period (1986-1995) and the first decade of the period (1956-1965) for minimum temperatures and the background of Tehran and Varamin also indicates a very high increasing rate of minimum temperature in Tehran, especially in November. Furthermore, the results show that the fifty-year trend (1951-2000) of Tehran's meteorological stagnation time series indicates a significant increase in minimum temperatures compared to background temperatures. In general, the average temperature of Tehran has increased during this period, but the rate of increasing growth has not been uniform throughout the entire period. The rate of increasing growth of Tehran's temperature during the second twenty-five-year period (1976-2000), which coincides with urbanization and industrialization, has had a more upward acceleration compared to the first period (1951-1975). Consequently, a significant relationship seems to exist between the increase in temperature and urbanization and industrialization. This trend of significant increase in Tehran's temperature, especially the minimum temperature compared to the suburbs, which results from the effects of urban development and land use change, can have destructive environmental effects and local climate change consequences. Wind, by transporting suspended particles and gases present in the urban atmosphere, reduces greenhouse effects and consequently prevents the increase of minimum temperatures in metropolises. Therefore, wind is the most important factor that causes a reduction in the temperature difference between the city and the suburbs. The Tehran metropolis is under the influence of local mountain-to-plain and plain-to-mountain winds most of the time. The role of these winds in transporting air pollution and suspended particles is very important; on the other hand, the wind field, especially local winds, is heavily influenced by urban effects. Therefore, any reduction in wind speed can cause irreparable effects. The results obtained from studying the fifty-year (1951-2000) time series trend of Tehran's wind field indicate a decrease in nocturnal wind speeds. Given Tehran's special geographical location and its proximity to the Alborz mountain range, air ventilation from its northern and eastern areas occurs less frequently; thus, with the reduction of northern winds, air ventilation and the escape of suspended particles from north to south also decrease, resulting in favorable conditions for air stagnation over the city and an increase in minimum temperature. Additionally, the relationship between the decreasing trend of Tehran's nocturnal wind speed and urban development and the expansion of construction seems logical. Therefore, further urban development will intensify the decreasing trend of mountain-to-plain winds and, consequently, the rate of increase in minimum temperature and air pollution in Tehran will take a more upward acceleration.
خلاصه ماشینی:
To investigate the effects of urban development and land use change on some meteorological quantities in the Tehran metropolis, a comparison between temperature and wind trends in Tehran and Varamin over a forty-year period was conducted.
Calculating the difference between the averages of the last decade of the period (1986-1995) with the first decade of the period (1956-1965) for minimum temperatures and the background of Tehran and Varamin also indicates a very high increasing rate of minimum temperature in Tehran, especially in the month (Refer to the page image) have more absorption and storage of thermal energy) which has caused significant changes in Tehran's temperature field compared to its suburbs, and Tehran's specific geographical location has also intensified these effects.
(Refer to page image) Figure 5 Monthly and annual average trends of Tehran's maximum temperature during two 25-year periods (1951-1375 and 1976-2000) The increased temperature of cities is due to anthropogenic heat production from buildings, greater absorption of incoming short-wavelength radiation, reduction of long-wavelength radiation due to pollution in lower layers, and a noticeable increase in temperature due to reduced heat flux by urban surfaces such as sidewalks and roads.
Usually, wind speed in the morning is less than in the middle of the day, but the fifty-year decreasing trend of the monthly average wind speed time series of Tehran (Mehrabad) expresses the very significant effects of land use change (Refer to page image) is upon the nocturnal winds.
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