Investigating and analyzing of urban climate comfort in present and future conditions based on climate change scenarios and regression methods in a coastal area

Introduction
The increase in temperature caused by human activities and the type of structure of the urban environment has an effect on the heat island. Extreme weather changes the climatic comfort in the human habitat, which causes the period of climatic comfort to exist with different characteristics in different regions and affect human health and comfort as well as the pattern of tourism development. Considering the effect of global warming and changes in climatic parameters in today's urban development and the need to create ecological stability between nature and human artifacts, discussion and investigation on the effect of micro climate factors on environmental and thermal comfort in urban spaces have been proposed as one of the important factors in quality urban spaces. The northern regions of Iran have a vast territory and diverse topographical and climatic conditions. Meanwhile, the southern regions of the Caspian Sea are rich in natural landforms and various tourism resources. With the warming of the global climate, the study of the comfort of the tourism climate in these areas should be given more attention and become one of the important subjects of the study of the climate of human habitation as well as the study of the resources of the tourism climate. However, the current research on climate comfort in Iran, especially in the northern regions of Iran, is very little, and few studies have been conducted on the analysis of comfort conditions under severe weather in the present and future time period and the investigation of possible changes. Therefore, in this study, the conditions of climatic comfort and human comfort were studied with regard to global warming and climate change scenarios in the southern regions of the Caspian Sea.
 
Materials and Methods
The study area includes Babolsar city one of the coastal cities of Mazandaran province, northern Iran, which is located between the southern shores of the Caspian Sea and the Alborz Mountain at 52º 39́ and 30̋ of longitude and 36º and 43́ of latitude and has an area of about 248.6 km2. Due to the low altitude of this area (-21 meters below sea level), the summers are hot and humid (often sultry), the winters are mild and humid, and frost is rare. The long-term average temperature and annual precipitation in this city are 17.8 °C and 939 mm, respectively. Due to its vicinity to the Caspian Sea, tourism services have been developed in this city and it is one of the best tourist destinations (about 6 million tourists per year) in Iran. Climate change and global warming have increasingly caused extreme events and stresses, and when investigating the conditions and patterns of changes in climate and tourism data time series, in addition to examining the average data, the extreme values ​​of the data time series that cause extreme discomfort and stress should also be considered. Therefore, The main purpose of this study is to investigate and identify the temporal patterns and trends of thermal discomfort based on different comfort-discomfort indices and affected by changes in climatic parameters in the historical period of 1987-2016 and based on future climate scenarios (SSP126, SSP245 and SSP585) from the GFDL-ESM4 climate model in two periods of 2020-2059 (near future) and 2060-2099 (far future) in the coastal and tourist-friendly city of Babolsar, located in the northern regions of Iran and the southern shores of the Caspian Sea. For this purpose, different values (especially extreme values) of daily temperature, relative humidity and wind speed were analyzed in different seasons. Then the comfort-discomfort indices including Effective Temperature Index (ET), Temperature and Humidity Index (THI), and Beiker Bioclimatic Index (Cp) were calculated for all the scenarios and time periods studied and the trend of changes was investigated on different values of these indices (especially limit tails of data) as well as the climate variables studied 
in the historical period and based on different future scenarios using the method quantile regression.
 
Results and Discussion
The study of the trends in climate parameters and climate comfort indices has shown that in the historical period, temperature and wind speed have increased in all seasons, but relative humidity has decreased. According to the optimistic scenario, various values of temperature and wind speed will increase in the near future period (2020-2059) (with a slope of 0.54°C per decade and 0.03 m/s); while for the distant future period, only a significant increase in winter (0.4°C per decade) will still exist. However, relative humidity will increase in the near future in spring and summer, but in the distant future, relative humidity values will decrease in spring and winter but increase in summer. However, no significant trends will be observed based on this scenario in the autumn. Therefore, it can be said if optimistic conditions are established for the future period, we can witness no change in high temperatures and an increase in days without heat stress, especially in summer (reduction of air humidity). Also, since the wind plays a role in cooling the environment, increasing the wind speed based on this scenario along with a small change in temperature can reduce thermal stress. According to the average scenario, the temperature will increase in both periods (0.5, 0.44, 0.5 and 0.3 °C per decade, respectively), while the relative humidity in the spring and winter seasons will increase (1.6% and 2.2% per decade) but will decrease in summer and autumn in the near future (-1.4% and -0.3% per decade, respectively). However, a decreasing trend for wind speed in winter (-0.34 m/s per decade) and an increasing trend in spring and autumn (far future) (0.18 and 0.05 m/s per decade) will be observed. But according to the pessimistic scenario, temperature values will increase in all seasons (respectively 0.7, 0.5, 0.75 and 1 °C per decade) while the relative humidity in winter will increase (1.8 % per decade), but it decreases in other seasons (spring, summer and autumn, -0.7, -2.5 and -0.6 % per decade, respectively). However, a possible increase for wind speed will occur in summer, autumn and winter (0.1, 0.07 and 0.3 m/s per decade, respectively) (mainly in the far future). Therefore, if the climatic conditions continue in the same way or move in the direction of more production of CO2 and greenhouse gases, it is possible to witness an increase in the number of days with climatic discomfort in the near future. Climatic comfort indices (ET, THI and Cp) have increased in all seasons in the historical period. According to the optimistic scenario, ET and THI indices will increase in the near future only in spring, summer and winter, while there will be no change in autumn. But in the far future, a significant increase will occur in most seasons (except summer) for this index. The lack of increase (for ET and THI) and decrease (for Cp) changes in summer based on optimistic conditions indicates no increase in thermal discomfort conditions in this hot season of the year. However, based on the average and pessimistic scenario, the ET and THI indices will increase significantly, but the Cp index will decrease significantly (increase in hot and hot conditions). The intensity of changes will be greater for high values of ET and THI, which indicates a noticeable increase in the number of days with high stress and thermal stress, and towards the pessimistic scenario and the far future, the number of hot and warm days will increase. Based on two average and pessimistic scenarios, in the near future, the number of hot and warm days and uncomfortable conditions will increase in most cases, but in the far future, in 
addition to increasing the number of days with heat discomfort, the number of days with cold conditions and comfortable conditions will also decrease and the days will tend to get warmer.
 
Conclusion
The results of the study have shown that the period of discomfort will occur based on and under the influence of changes in meteorological and climatological variables affecting each discomfort index, and awareness of the weather conditions associated with periods of high thermal discomfort levels will help to management and reduction heat stress through the development of early warning systems. The number of days with high heat stress conditions (hot and sultry conditions) will potentially increase towards pessimistic scenarios, and the possibility of human discomfort due to high heat (and sometimes high relative humidity) not only will increase in the warm months of the year, but also in cold months, while cold and cool conditions decrease. The results of the study on a seasonal scale have shown that discomfort periods will occur based on and influenced by changes in meteorological and climatological variables affecting each discomfort index, and knowledge of the weather conditions associated with periods of high thermal discomfort levels will help manage and reduce heat stress through the development of early warning systems. Therefore, the results of this study are very important due to the importance and direct impact of climatic parameters on human health, and city officials should design and create environmental strategies to reduce the effects of heat in the city. However, due to the lack of meteorological stations with a high concentration in the region, the analysis was inevitably carried out on one station but on different time scales, and this issue has limited the results. Therefore, in future studies, it is suggested to carry out investigations on a spatial-temporal scale and with several climate models.