A Study On The Urban Heat Island Effect In Nanjing

Recently, as a result of people's concern with the urban environment as well as frequent appearance of abnormal high temperature in city, scientists have paid more attention on urban heat island (UHI) research. Quantitative monitoring, analysis and evaluation of urban heat island effect, has become one of important part of current urban climate and environment study, also is an important aspect of global change research. In this paper, the variation characteristics of Nanjing UHI in different time scale have been analyzed based on the daily air temperature data during 1966-2005 which include the average temperature, the daily maximum temperature and the daily minimum temperature from 3 weather stations in Nanjing area. Meanwhile, by retrieving land skin temperature (LST) of study area from ASTER and Landsat-5 TM thermal infrared channel data via ASTER split-window algorithm and TM6 Mono-window Algorithm, the paper also quantitative analysis the spatial distribution characteristic of Nanjing UHI in summer and its relationship with land-cover types. The main conclusions of research are as follows:(1) The variation characteristics of Nanjing UHI in different time scale Using the air temperature observation from XiaoJiaoChang station represents urban temperature and mean value of observations from LiuHe and JiangPu station represents suburb temperature, their difference as the intensity indicator of Nanjing UHI effect. The results show that since the existence of UHI effect, urban air temperature is higher than that of suburb area, and its average difference value is 0.28℃in recent 40 years. The inter-annual change of UHI effect has three development stages: it weakened in 1960s, low-level fluctuated during 1970s-1990s, and increased rapidly after 2000.The two jumps are 1970, 2000. The annual variation of UHI presents remarkable wave characteristics, the maximum and minimum monthly averages occur in February and June. For seasons, UHI effect appears strong in winter and weak in summer, meanwhile it strengthened remarkable in fall. The UHI effect at night is stronger than it in daytime in general case and the difference is most significant in autumn.(2)The spatial distribution characteristics of Nanjing UHIThe spatial distribution of Nanjing UHI is consistent with the outline of urban built-up areas and appears expansion trend with the urban development. There are several distinct heat centers in Nanjing urban area in summer. These centers are either industrial zone with high energy consumption and heat intensity or commercial residential area and large public places with high albedo and population density. The distribution of surface temperature and land cover types has a good consistence. Urban land and bare ground have high mean skin temperature, the vast majority of contribution to the city heating comes from those two land types, vegetation cover land usually has normal skin temperature, and water temperature is the lowest. Obviously water and green land in city have a positive effect to reduce UHI.