Characteristics And Simulation Studyof Hangzhou Urban Heat Island

To investigate the causes and the characteristics of urban heat island effect of Hangzhou and the influence of city,water and the anthropogenic heat on accuracy of simulation of air temperature, the data of observation between1981and2010Hangzhou weather stations and automatic weather station data, NCEP reanalysis data, MODIS product and WRF model were used.(1)The results base on observation shows that:the probability of urban heat island of Hangzhou is about97.8%.most of the heat island intensity ranged between0.5℃and2.5℃. The average annual heat island intensity is above1℃and the maximum heat island intensity can reached3.0℃. UHI is more stronger and more stable in nighttime than it is in daytime, with maximum UHI intensity reaching1.627℃at23:00and maximum UHI intensity reaching0.149℃at15:00.(2) By using Landsat/TM and ETM+data, remote sensing inversion of surface temperatures shows that:(1) the surface temperature of the main city of Hangzhou, especially the old town surface bright temperature is higher than the surrounding area obviously. It is the urban heat island.(3) The results base on wrf model shows that:autumn and winter heat island intensity is the strongest, followed by summer and spring, As to the diurnal variation, the four seasons also testify that the night heat island intensity is greater than in the day, in spring is24:00at night, at22:00in the summer and in autumn is at21:00and in winter at24:00is the most strongest, in spring at12:00t, at10:00in the summer and in autumn is at14:00and in winter at12:00is in the day is the weakest.(4)The urban heat island in o summer is about1℃, the characteristics of land surface is abnormal. The mixed layer is formed fast when the thermodynamic and dynamic interaction, the turbulent kinetic energy is about0.9-1m2/s2, the boundary layer height can reach2400m in the daytime, the boundary layer height is about300m at night, the temperature above Hangzhou is more higher than the other areas, the surface of200meters is the most obvious, the airflow through the city will have a local city heat island circulation, the sensible heat fluxin in city is more higher than in suburbs, the latent heat flux in suburbs is more higher than in city, (5) The results base on wrf model also shows that although anthropogenic heat has a warming effect on day temperature obviously, the average temperature has risen by0.6℃-0.7℃; so the human thermal simulation results which involve anthropogenic heat is more accurater. The water is playing a important role in the temperature of Hangzhou, in areas where river surface is replaced by urban underlying surface, the nighttime temperature has risen by2℃.with the expand of city, the heat island intensity is different in different seasons, winter heat island intensity is much greater than the summer, the highest temperature can reach to2℃while the summer heat island intensity is unobvious, the city near the ground temperature is almost unchanged.The experiment of surface albedo shows that:when the surface albedo decreases, the surface temperature will increased, and the more surface albedo decreases, the more the temperature increase.