Abstract: Background, aim, and scope Withing the implementation of the western development policy, Xining entered a rapid development stage at the end of twentieth Century, and the scale of the city has been expanding, which has caused the urban heat island effect to become more and more prominent. Therefore, it is of great significance to study the spatial and temporal evolution characteristics and mitigation measures of urban heat island effect in Xining for the sustainable development of Xining. Compared with previous studies, the general urban heat island studies mostly take the urban administrative boundary as the suburb boundary. This paper takes the urban built-up area boundary as the urban and suburban boundary, and is relatively new. Materials and methods Using the Landsat satellite image from 1987 to 2015 and the same period of meteorological data and economic data, selected the single window algorithm to retrieve the surface temperature in Xining City from Landsat satellite image, combined with the thermal field variation and years of built-up area of the boundary,then the characteristics of temporal spatial evolution of Xining City urban heat island effect is analyzed in this paper. At the same time, the relationship between heat island intensity and vegetation, impervious surface, population and other factors was discussed. Finally, it puts forward the regulation measures of urban heat island effect in the process of urbanization. Result The results show that: (1) In summer in Xining city as "heat island" effect, "cold island" effect in winter. (2) The intensity of heat island in Xining city at the time is divided into three intervals, 1987~2000 years of heat island effect enhanced slowly from 2000 to 2003 is the rapid increase of 2003 to 2011, the heat island effect gradually weakened, from 2011 to 2015 the heat island effect, strength remained unchanged. (3) The same trend area of summer heat island area and trend of winter cold island, and built-up area change. Discussinon The change of the heat island area in Xining shows that 2000 has become an important time node for the change of thermal environment. Before 2000, the area of heat island in Xining increased little, but there was a sharp increase after 2000. This is due to the implementation of the western development policy. Xining has expanded rapidly in the original built-up area, making the city development from a single center to a multi center structure, and the increasing rate of greening can not catch up with the speed of development. Combined with the actual situation in Xining, this paper puts forward four relief measures for the heat island effect. (1) The artificial lakes should be dug near the industrial zone and the park. (2) Private cars should be controlled. (3) Green energy, such as abundant solar and wind energy in Qinghai Province (3) Construction the counties around Huangzhong, Huangyuan and other Xining cities to attract and disperse the population. Conclusions Research shows: (1) There was almost no change of heat island area in Xining before 2000. After 2000, the area of heat island area, especially the area of strong heat island area and medium heat island area, increased rapidly. In 2003, the area of heat island area reached the highest. From 2003 to 2011, the area of heat island gradually decreased, but increased again after 2011. (2) During the summer daytime, the intensity of urban heat island in Xining is positively correlated with the number of vehicles, built-up area, population and NDBI mean, and negatively correlated with urban greening rate, NDVI mean and BCI. (3) In winter daytime, the intensity of urban heat island in Xining is positively correlated with urban greening rate, NDVI, NDBI, BCI, and negatively correlated with the number of vehicles and built-up area. Recommendations and perspectives Due to the lack of remote sensing data and the poor quality of remote sensing data, the final screening image is not continuous in time, and the final result may lose some information. If there are more image data, better results should be obtained. In the study, it was found that during the winter, Xining was an obvious “cold island” in the daytime. Some studies have shown that the urban area in winter is “heat island” at night. However, due to the limitation of the imaging time of remote sensing data, the night thermal environment in the built area has not been studied in this paper. In future studies, we will focus on the heat island effect of winter nights in Xining.
Keywords: urban heat island effect; single window algorithm; land surface temperature retrieval; BCI; thermal field variability index; Xining City