Quantitative Assessment and Planning Simulation of Beijing Urban Heat Island

In order to quantitatively evaluate the current situation of the urban heat island and forecast the trend of the heat island development for Beijing in future, air temperature data, remote sensing data and the city planning data are used to monitor and assess the current heat island and simulate the future heat island distribution in Beijing. Based on the distance between the central of Beijing urban and 20 different weather stations, the weather stations are divided into three distinct types such as the exurban, suburb and urban stations, which the annual mean air temperature is corrected by the sea level elevation, respectively. The temporal variation of the annual mean air temperature is estimated from the difference of average air temperature between urban stations and exurban stations for the period of 1971—2012. The intensity and spatial distribution of the heat island for Beijing and six-district regions is obtained using two indexes of the heat island intensity and heat island proportion from the two different spatial resolution satellite data. They are NOAA/AVHRR and Landsat-TM, respectively. The heat island of Beijing plain area is evaluated, too. Using the monitoring result of the urban heat island intensity in 2008, together with the land use types of city planning for 2020 in Beijing city, the heat island in 2020 is simulated. Results show that temporal change trends of the urban heat island obtained from the observations of weather stations and remote sensing have a good agreement. The difference of the temporal and spatial distribution of the heat island from different satellite data is small. For example, the warming rate of the city heat island intensity is 0.33 ℃·(10 a)-1 with the mean of 1.12 ℃ in recent five years(2008—2012) calculated from the annual mean air temperature. Observed results from the remote sensing show that heat island intensity has consistently enhanced for the period of 1987—2001. However, after 2001, the intensity and area range of the heat island is reduced for 2004 and 2008 owing to the successful Olympic bid, large-scale old city reconstructions and greening measures implemented. After 2008, the heat island spatially expands except the direction of west and the blending of Tongzhou, Shunyi, Changping and Daxing district with the central city tends to be obvious. Percent of the heat island area in six-district regions rises from 31% in 1990 to 77% in 2012. Based on the heat island intensity scores, the top three of the heat island intensity is Chengqu, Haidian and Fengtai, respectively and Yanqing is the least influenced by the heat island. The simulation results of the urban heat island for 2020 show that the pattern of the Beijing heat island will be changed from the urban center-sprawl to center-periphery. The intensity and scope of heat island in six-district regions will be obviously decreased but the small distributed heat island will be more around the exurban. The area of the heat island in the six-district regions will decrease from 77% in 2012 to 60% in 2020, which shows the difficult and complexity of reducing the urban heat island only based on the city planning for Beijing.