formation of urban heat island and its effect on temperature variability in Babol

Introduction
Urbanization and cities have a great impact on human life. Today more than half of the world's population living in cities. Changes due to urbanization has negative consequences on environmental, social and economic characteristics. Today, one of the important impacts of the city is the change in environmental characteristics. Cities reduce the amount of albedo and radiation from the ground. Due to changes in the radiation balance in cities, one of the consequences of their development is the change in temperature characteristics. The most famous city's impact on the climate is the urban heat island. UHI can be better detected at a minimum temperature. Mostly Cities have higher minimum temperatures from suburbs. In addition to the temperature differences between the city and the suburbs, some studies have shown that the behavior of urban areas is also different. The purpose of this study is to investigate the formation of UHI and day to day changes in Babol and its suburb temperature. This work try to Understanding the best time of UHI formation in Babol every day, as well as looking at the best time between different months of the year.
Materials & Methods
This study was conducted on Babol city in Mazandaran province. There are several methods for identifying UHI, which typically include the use of climatological data from the environment, satellite imagery, or mathematical modeling. Due to the lack of a meteorological station in Babol, two data logger (MIC 98583 USB-Data Logger, Taiwan) with the ability to record temperature and relative humidity data at different times in the city and suburbs were installed. These devices were calibrated by the manufacturer and tested at the meteorological station before starting up the devices in the environments. This research investigates day-to-day temperature variations in both urban and suburb locations to show spatial differences. 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:
DTD=(∑▒|t_i-t_(i-1) | )⁄((n-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:
∆DTD=DTD(tmax)-DTD(tmin)
ΔDTD is the difference between day to day variability of daily Tmax (DTDtmax) and day to day variability of daily Tmin (DTDtmin).
The conventional method was also used to illustrate the thermal island intensity. The difference between the temperature of urban centers and surrounding rural areas (∆Tu-r) indicates the intensity of the island heat.
Results and discussion
To understand the temperature behavior of the city and suburb, hourly temperature data was extracted for two environments. The survey showed that from 9 to 13, the intensity of the UHI has lowest amount. The lowest temperature difference is around 11 am. In other words, the city's impact on temperature is at its lowest amount. In general, the average temperature in the urban environment is about 19.5 degrees Celsius and in the suburb it is 18.5 degrees. The UHI intensity according to minimum temperature is 1.7 ° C throughout the entire survey period. In addition, temperature difference between the city and the suburbs was more pronounced during December, January and February. The survey showed that DTD for mean daily temperature and minimum temperature, in city is more than the suburbs, but this index for the maximum temperature is not much different in the two environments. The city's ΔDTD is higher than the suburbs. The study of the urban and suburb humidity showed that the urban average is about 70% and the suburbs also have about 73% relative humidity. There is the highest humidity difference between the urban and the suburbs in the morning, because at this time suburbs having a lower temperature than the city.
Conclusion
According to the findings of the discussion, it can be said that the temperature difference between the city and the countryside observed in Babol is due to the effect of the city on the temperature, in other words, the UHI is formed in the city, and this phenomenon is clear in minimum temperatures. The results of the temperature study in Babol showed that the minimum temperature in every month was higher than suburbs, while the maximum temperature of urban in many cases was less than the suburbs. In the urban station during the period under review, the minimum temperature has not fallen below 2 ° C, and in the suburbs the lowest recorded temperature is -0.8 °. The study of the daily variability of temperatures also showed that the ΔDTD index, which is a new and alternative indicator for identifying the UHI phenomenon, is lower in the suburbs. Since the built up environment reduces the amount of albedo and emissivity from the ground, and it is generally less moisture and the heat and energy reaches a higher level, more Tangible heat will be stored within the built-up space.
According to the findings of the discussion, it can be said that the temperature difference between the city and the suburbs is as a result of the city's effects on the temperature, in other words, the thermal island in Babol has been formed and this mode has been shown more clearly in its minimum temperatures.