The influence of green spaces on land surface temperature and humidity of the surrounding environment in Bushehr city

 The increase in impervious surfaces due to the urbanization has caused many adverse effects on urban ecological systems, including the urban heat environmental risk. Revealing the relationship between land use/land cover composition and land surface temperature (LST) gives insight into how to effectively reduce the temperature in urban environments. In recent years, the expansion of Bushehr city has resulted in an increase in impervious surface, the decrease of green space and a significant change in the temperature. It is also essential to determine the influence of green spaces on the surrounding environment in urban planning of Bushehr.

 In order to reveal the comprehensive effects of green space on the urban thermal environment in the severely hot regions, this paper adopts remote sensing technology to extract and analyze green space, land surface temperature (LST), and land cover (LC) from the Landsat spectral imaging data (August 2018) with clear-sky conditions. A field survey was carried out in August 2018 and temperature and relative humidity was recorded for 13 selected green spaces in the Bushehr city. To analyze the field data, a multivariate linear regression model between temperature and relative humidity with three variables of direction, distance, and the size of green spaces was determined and interactions between variables were investigated. By applying a multivariate regression model, the relationship between temperature and relative humidity data was calculated for each point. Tukey test was carried out between the averages of temperature variations and relative humidity for each of the three variables at a 95% confidence level.

 The results of the R2 correlation coefficient from the linear regression model between normalized difference vegetation index  (NDVI) and land surface temperature equal to 0.72 indicated a high correlation between temperature and NDVI variations. The results of the temperature variation analysis with NDVI changes indicated that NDVI variations, which are actually plant frequency indices, were one of the most important factors in reducing temperature or in improving the most important ecological function of urban green space. The results of the recorded data at different intervals and directions from the green spaces indicated a gradual decrease in temperature and an increase in relative humidity by reducing the distance from the green spaces. Accordingly, the effect of green spaces on temperature and relative humidity was significant up to a distance of 60 meters (p≤0.05). The western direction had the lowest temperature and the highest relative humidity and the eastern direction had the highest temperature and the lowest relative humidity. The R2 correlation coefficient obtained from the linear model between temperature and relative humidity with the interactions between the three variables (direction, distance, and the size of green spaces) were also 0.88 and 0.95, respectively.

 The results indicated that urban green space plays a significant role in improving the urban thermal environment. By using remote sensing technology and comparing the thermal environments, we conclude that the location and distance of urban green spaces affect the thermal pattern in an urban environment. We can establish certain rules on the distribution of the urban green space and the cooling ranges in hot seasons in the surroundings of urban green spaces.