Research On The Urban Thermal Environment Of Suzhou City Based On The Method Of Local Climate Zoning

Based on the Local Climate Zones(LCZ)system,in this paper,the Landsat images were used to create the LCZ classification of the Suzhou area in 2017.Accordingly,the site observation method and the numerical simulation method were used to study the urban thermal environment of Kunshan City and Suzhou City from the LCZ plot scale.The impact of urbanization development on the thermal environment of Suzhou was explained by replacing the underlying surface data of WRF with the built-in MODIS underlying surface and the LCZ underlying surface in 2009.In this paper,the transport effect of the upstream cities on Suzhou was studied by replacing the underlying surface of Changzhou and Wuxi with farmland under favorable weather conditions.The cooling and energy saving effects of four different mitigation measures which are from the perspective of building and air conditioning systems were also studied in Suzhou.The main conclusions were as follows:Combined with the site observation method,the results showed that: The urban heat island intensity(UHII)was strong at night but weak during the daytime in Kunshan.In terms of seasonal variation,the average UHII was the strongest in autumn and the weakest in summer.The range and intensity of the UHI in Kunshan were expanding year by year.It was found that the heat island intensity of different LCZs was significantly different,and the higher the urbanization degree of the land,the stronger the heat island effect.Combined with the numerical simulation method,the results showed that: The WRFBEM-LCZ model could accurately simulate the temporal and spatial variation characteristics of various meteorological elements in the surface and boundary layer of Suzhou.The temperature distribution in Suzhou showed a decreasing trend from the city center to the surrounding area.In terms of the boundary layer structure characteristics,the distribution of temperature,wind speed and vapour mixing ratio of different LCZs showed a strong correlation with local human activities,land cover,spatial morphology,material structure and other physical properties in Suzhou.The results of the impact of urbanization development on the thermal environment of Suzhou showed that: The rise in urban temperature could be explained as a change in physical characteristics caused by urbanization.Urban expansion was the main factor leading to regional warming during the urbanization development.The strengthening of lake wind caused by urban expansion was helpful to alleviate the UHI in the lakeside area.The urban high street valley had a certain improvement effect on the local thermal environment at midday.From 2009 to2017,the urbanization in Suzhou had been changing from natural to urban LCZ type,and at the same time,the urban structure had become denser and higher.During this period,the nighttime temperature increase of Suzhou increased from the downtown area to the outskirts of the city.The increasing and decreasing temperature areas were distributed in patches in the daytime.The difference distribution of sensible heat flux was similar to that of 2 m air temperature in the daytime.The urbanization also led to an increase in temperature and heat index and a decrease in relative humidity for all LCZs.The heat index had reached the level requiring special attention at night,and had been in the dangerous level during the day.The results of the influence of upstream cities on the thermal environment of Suzhou showed that: The influence of the upstream cities on the 2 m temperature distribution in Suzhou was consistent with the difference distribution of 10 m wind.The impact of upstream cities on the temperature in the boundary layer of Suzhou was highly related to the stability of atmospheric stratification.The formation of urban agglomeration led to both the surface UHI and the upper air cold island effect.The upstream cities had different influence on the surface specific humidity of Suzhou from that of temperature.At 14:00,due to the vertical turbulent and heat island circulation,zonal high value areas of the decreasing humidity were formed around the west and south of the city.The upstream cities had significant influence on the distribution of specific humidity in the boundary layer of Suzhou,and the decreasing effect in the daytime was obviously higher than that at night.Urban agglomeration caused dry island effect on the ground and wet island effect on the upper air.The results of different mitigation measures showed that: The cooling effect of thermal insulation material was obvious at night,but it caused the local temperature increase of LCZ 2and LCZ 4.During the daytime,the cooling effect was worse.This measure had little effect on air-conditioning energy consumption.The cooling effect of high albedo roof was obvious during the day,but almost no effect at night.This measure had a certain energy saving effect,and each energy consumption difference grade had a good correspondence with LCZ type.Increasing the COP(Coefficient of Performance)of air conditioner couldn't bring about significant changes in temperature,but it could bring about a significant reduction in energy consumption throughout the day.The energy saving effect was highly correlated with the building type.Increasing the indoor setting temperature led to the decrease of the temperature of all LCZs at night,and the cooling range of the open building areas which were concentrated distribution in the city was larger.In general,the mitigation measures based on building characteristics had better cooling effect,but might lead to increased energy consumption.The mitigation measures based on air conditioning system had remarkable energy saving effect,but the cooling effect was not ideal.