چکیده:
تراکم جمعیت در شهرها سبب افزایش دمای ناحیة مرکزی میشود. هدف از این مطالعه بررسی اختلاف دمایی ناشی از جزیرة حرارتی و اثر آن در تغییرپذیری دمای شهر بابل است. از سه دستگاه دیتالاگر ثبتکنندة داده در محیطهای بافت متراکم شهری، حومه، و فضای سبز شهری استفاده شد. تغییرپذیری دما و رطوبت نسبی به مدت هشتاد روز (۱۵ تیر تا ۳۱ شهریور ۱۳۹۴) با گام یکساعته بررسی شد. اختلاف دمای میانگین ایستگاه شهری با حومه ۱ و با فضای سبز ۸/۱ درجه بوده است. کمترین میانگین رطوبت در محیط شهری (۶۷ درصد) و بیشترین در فضای سبز (۷۷ درصد) مشاهده شد. اختلاف روزبه‌روز دمای میانگین (DTD(tmean)) و روز به روز دمای بیشینه ((DTD(tmax) شهر از حومه و فضای سبز بیشتر است، اما اختلاف روزبه‌روز دمای کمینه ((DTD(tmin) در شهر کمتر از دو محیط دیگر است. تفاوت تغییرپذیری دمای بیشینه و کمینه (DTD∆) شهر از دو منطقة دیگر بیشتر بوده و در فضای سبز تقریباً صفر است. این میزانها بیانگر تغییرپذیری بیشتر دمای شهر است. نتایج نشان میدهد جزیرة حرارتی ایجادشده در بابل در تغییرپذیری روزبه‌روز دمای آن مؤثر است. در شهرهای متوسط میتوان اثر جزیرة حرارتی بر دما و رطوبت را دید و فضای سبز در کاهش دمای بابل نقش مهمی دارد.
Heat island and summer temperature variations in the different environments of Babol city, Mazandaran
Introduction
The rapid growth of urbanization formed in the 19th century after the industrial revolution in the developed countries and after that the urban area of many cities extended rapidly. In those cities many different activities such as transportation, industrial and construction activities is much higher than rural environments, while in that environments vegetation and green spaces are lower. Thus, these activities cause the increased level of temperature in the urban environments compared to surrounding areas which this phenomenon is called “urban heat island” (Oke, 1973). This phenomenon is one of the main concerns in the urban environments due to its impact on biological, meteorological, environmental, social and economical aspects. For instance, urban head island causes earlier bloom and the blossom of plants and trees, prolongation of the growing season. Thus, Babol is one of the densely built cities of Mazandaran province, which is confronted with rapid population growth during few last decades. The aim of this research is to investigate the impact of urbanization on heat island and day to day temperature variation in that city.
Materials and methods
The study area was conducted in the Babol city, Mazandaran. Due to the lack of meteorological station in the Babol city, three devices with data logger (MIC 98583 USB-Data Logger, Taiwan) were equipped to record temperature and relative humidity in three environments urban, suburban, and green. The temperature and relative humidity were recorded every hour throughout the course of 80 days (July 6 to September 22) in 2015.
The monitoring boxes were placed at a height of about 2.5 m above the ground surface. This study is investigated the day to day temperature variation with respect to the impact of urbanization on temperature variations. For this purpose, the two following integrated methods were used: 1) the day to day temperature variation (DTD); 2) the difference between day to day variability of daily maximum temperature (DTD max) and day to day variability of daily minimum temperature (DTDmin) (Tam et al., 2015).
The day to day temperature variation is based on the following equations:
Equation 1:
Where Σ is the sum over all n data elements, t is daily temperature, i is the counter that marches through the days in a time period (e.g. a month),| | is the absolute value, and n is the number of days elements.
Equation 2:
ΔDTD is the difference between day to day variability of daily Tmax (DTDtmax) and day to day variability of daily Tmin (DTDtmin). A positive value indicates greater day-time day to day temperature variation and a negative value indicates greater night-time day to day temperature variation (Tam et al., 2015). The significant difference for temperature (maximum and minimum) and daily relative humidity in different environments was tested using the one-way analysis of variance (ANOVA); and then the day to day variability of temperature was calculated based on a DTD and ΔDTD equations for all three environments. Analysis of the data was conducted using Excel and R software.
Results and discussion
The difference between the mean temperature of urban and suburban environments in our study area is around 1°C and this difference between urban and green environments is around 1.8°C. The mean relative humidity in the urban and green environments are minimum (67%) and maximum (77%), respectively. Day to day temperature variation of daily temperature DTD(tmean) and temperature maximum DTD(tmax) in the urban environment is higher than suburban and green environments, but the day to day temperature variation of daily temperature minimum DTD(tmin) is less than the two other environments. The difference of DTD(tmax) and DTD(tmin) in the urban environment is higher than the two other environments and is nearly zero for the green environment. These values indicate higher variation of the daily temperature in the urban and a very small difference in the daily and nightly temperatures variation for the green environment. The results of this research demonstrate that the heat island not only affects the temperature in Babol city, but also influences its day to day temperature variation.
Conclusion
Based on these results, one could observe the impact of urbanization on climatic parameters in particular temperature and humidity. Moreover, the green environment can play an important role on the climate change of Babol city.
Keywords: urban heat island, temperature, day to day temperature variation, relative humidity, Babol city
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