The effects of urbanization and Heat island over summer temperature variations in Babol

Introduction
The rapid growth of urbanization formed in the 19^th century after the industrial revolution in the developed countries. After the revolution, the urban areas of many cities extended rapidly. In those cities many different activities such as transportation, industrial and construction activities is much higher than rural environments. In the urban environments, vegetation and green spaces are lower than those in rural areas. Thus, these activities cause the increased level of temperature in the urban environments compared with surrounding areas. This phenomenon is called “urban heat island”. This urban heat island is one of the main concerns in the urban environments due to its impacts on biological, meteorological, environmental, social and economic issues. For instance, urban heat island causes earlier bloom and the blossom of plants and trees and also prolongation of the growing season. Thus, Babol is one of the densely built cities of Mazandaran province. It is confronted with rapid population growth during the few last decades. The aim of this research is to investigate the impacts of urbanization on heat island and day to day temperature variation in that city.
Materials and methods
The study area is 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) have been equipped to record temperature and relative humidity in three environments of urban, suburban, and green areas. The temperature and relative humidity have been recorded every hour throughout the course of 80 days (July 6 to September 22) in 2015.
The monitoring boxes have been placed at a height of about 2.5 m above the ground surface. This study has investigated the day to day temperature variation with respect to the impacts of urbanization on temperature variations. For this purpose, the two following integrated methods have been 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).  
The day to day temperature variation is based on the following equations:




 

(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),| | gives the absolute value, and n is the number of days elements.




 

(2)





Where, ΔDTD is the difference between day to day variability of daily T_max (DTDt_max) and day to day variability of daily T_min (DTDt_min). 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. The significant difference for temperature (maximum and minimum) and daily relative humidity in different environments has been tested using the One-Way Analysis Of Variance (ANOVA); and then the day to day variability of temperature has been calculated based on a DTD and ΔDTD equations for all three environments. Analysis of the data has been 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. This difference between urban and green environments is around 1.8°C. The mean relative humidity in the urban and green environments is minimum (67%) and maximum (77%), respectively. Day to day temperature variation of daily temperature DTD (t_mean) and temperature maximum DTD(t_max) in the urban environment is higher than those of suburban and green environments, but the day to day temperature variation of daily temperature minimum DTD(t_min) is less than those of the two other environments. The difference of DTD (t_max) and DTD (t_min) in the urban environment is higher than that of 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 have demonstrated that the heat island not only affects the temperature in Babol city, but also influences its day to day temperature variation.
Conclusion
The results of this research have indicated the impacts of urbanization on climatic parameters in particular temperature and humidity. The results have also revealed that the green environment can play an important role on the climate change of Babol city.