Study of the relations between climate and human comfort in urban environment using neurotic pressure index (Case study: Tehran city)

Introduction
Climate affects, more than any other factors, the type and form of human life, so that many cities that have made or developed regardless of climatic information are suffering from weather-related problems such as air pollution, water supply and flooding etc. By using the meteorological information in designing new cities as well as developing old cities can reduce the mentioned problems. Human comfort condition, based on the definition, is a thermal condition that is comfortable for at least 80% of people. Regarding the high impact of climate on human comfort, the humankind has been always looking for a suitable usage of the local climate. It was investigated the effective bioclimatic indices over human comfort in Shiraz city and their results showed that Shiraz with having a various bioclimatic condition holds a warm to very cold climatic conditions throughout the year. Attempt was made to study the climatic comfort index in Boushehr city. His findings from THI index indicated that the months of April, May, November, December, January, February and March are appropriate in terms of climate comfort for human. Investigation on the thermal comfort was made in Shahrud-Semnan from military viewpoint. In addition, the effect of climate on the architecture of Qom city was carried out by attempted to classify the climate based on effective parameters on life quality in Markazi province. Therefore, considering the high impact of climate on the human comfort as well as the spread of urbanization, in this research this subject is studied in the megalopolis city of Tehran.
 
Materials & Methods
Tehran city, in terms of climatic classification, possesses a warm and dry climate with an annual mean precipitation of approximately 250mm. The figure 1 shows the location under study and indicates climatology stations used.
 
 
Figure 1 geographical position of Tehran city and the stations under study
In the paper, the relations between three elements of temperature, relative humidity and wind speed is identified for 2 periods of 15-years from 1976 to 2005 for the selected stations in Tehran city and these data are studied using neurotic pressure index. This index is aimed to explain the level of comfort using temperature, humidity and wind. The index is stated as follows:
 
Where,
 is the digital index for comfort; is the effective temperature and humidity index supposing a calm weather;  is an index that adds up the effect of the surplus coldness resulting from the air motion
 and  are obtained from the following equations:
 
 
Where,
is temperature in Fahrenheit;  is relative humidity in %;  is the speed of wind in knots.
After obtaining digital index for comfort () from the above relation for finding the heating rate, the table 1 will be used.
 
Table 1 grading index for comfort related to humid in warm climate





index for comfort (CI)


Heating rate




Below -5


Cool climate with uncomfortable condition




Between -5 and -1


Cool climate




0


Comfortable condition




Between 1 and 5


Warm with comfortable condition




Between 6 and 10


Warm with uncomfortable condition




Between 11 and 15


Uncomfortable condition




Above 15


Fully uncomfortable condition





 
After estimation of the coefficients of the neurotic pressure index, for better indicating the variation of the heating index for comfort in Tehran, the zoning was carried out. With objective in this research, the existing methods including spatial interpolation, spatial analysis for data related to stations and inverse distance weighting (IDW) were used. Similarly in this methodology after defining the coefficients of the neurotic pressure index for two 15 periods including warm and cooling conditions , the index for comfort was extended to surface level and finally by using map of comfort variation and GIS software (Arc Map) the zoning map was developed as follows indicated in figures 2-5.
 
 
                   
 
       
 
Discussion of Results & Conclusions
The coefficients of the neurotic pressure index were evaluated for the selected stations for a 2-period of 15-years in different months of the year. The findings indicated that during the first period the thermal phase in the months of January, February and December was cold and with lack of comfort, so that the North of Tehran station possessed the most condition of the lack of comfort during the cold period of the year. In addition, during the hot period of the year also the months of May, June, July, August and September possessed a thermal phase with a lack of comfort to absolutely lack of comfort. Meanwhile, the months of March and October hold the best comfort condition as well as among the stations, Mehrabad, in comparison with other stations, was recognized as the best station in terms of climate comfort. Generally, the results for the second period also showed that these coefficients had an ascending trend in most of the months. On the other hand, the condition from a cold thermal comfort turned into a hot thermal comfort, which indicates an increase in the local temperature due to the climate change in the study area. The results of interpolation by GIS also indicated that in the cold period, there is strong lack of comfort in the northern areas of Tehran city, meanwhile an appropriate comfort condition was replaced during the hot period. But for the southern areas of the city, there is an appropriate thermal comfort condition during the cold period and a lack of comfort is replaced during the hot period, though.