The Research On Green Heart Planning Strategy Of Changsha,Zhuzhou And Xiangtan Urban Agglomeration Based On WRF Model

The urban atmospheric environment is an important part of the urban physical environment.The urbanization on space embody the process of replacing the natural open space with urban space.The reduction of natural green space in this process has led to a series of climatic problems and environmental problems,which have an adverse impact on urban residential comfort,residents'health and urban resource consumption.As the common open space of Changsha,Zhuzhou and Xiangtan,the Green Heart of Changsha,Zhuzhou and Xiangtan urban agglomeration should fully consider the regional climate carrying capacity in its planning.Therefore,the goal of this paper is to provide quantitative scientific data and optimization strategies for the green-heart planning of the Changsha-Zhuzhou-Xiangtan urban agglomeration.In this study,I select the sunny day of summer and the sunny day of winter as the typical cases,taking the green heart of Changsha-Zhuzhou-Xiangtan urban agglome-ration as the research object,using WRF(Weather Research and Forcasting Model)combined with UCM(Urban Canopy Model),three groups of experimental schemes are set up to correspond to the development of urbanization in different degrees within the Green Heart according to the Green Heart Planning Scheme of Changsha-Zhuzhou-Xiangtan Urban Agglomeration(2010-2030).Taking the actual development situation of urban agglomerations&green-heart and the meteorological background field in 2013 as the initial field of the model,the change of land use pattern within the green heart range as the only variable in the three groups of experiments,conducting a simulation test of atmospheric environmental sensitivity in the study area.This paper analyzed the variation characteristics of temperature field and wind field in the simulation results of sensitivity test,aiming at reducing the adverse effects of new urban land in the green-heart on the thermal environment and wind environment of the urban agglomeration,proposing strategies and establishing optimization plans respectively,and inputting it into WRF mode to test the optimization effect.The main conclusions are as follows:(1)In the green-heart planning of the Changsha-Zhuzhou-Xiangtan urban agglomeration,in the summer sunny days,when the urban area of the green-heart area is initially expanded,the temperature in the green-heart area decreases,and the temperature in the urban area remains basically unchanged.When the area of urban and construction land in Green Heart is further increased to half of the total area of green-heart,the temperature of the green-heart rises,the temperature difference in different parts of the interior becomes smaller,the temperature of the surrounding cities increases significantly,and the temperature of the near ground in Zhuzhou increases by 0.4°C?0.5°C.Xiangtan City and Changsha increases by 0.3°C?0.4°C.The green-heart itself has the function of regulating the temperature of the urban agglomeration area.When the proportion of urban land is raised to a certain extent,this function is weakened,and the temperature distribution and the daily temperature change process of the green-heart tend to be the same level in the surrounding cities.In the winter sunny days,as the urban area increases within the green-heart,the temperature in the green-heart area decreases,and the urban temperature rises within0.1°C.The urban heat island effect is remarkable.In winter,the heat island is stronger and lasts longer on sunny days.The change of land use pattern in the green heart slightly enhanced the intensity of urban heat islands.In the summer sunny days,the growth rate of Changsha and Xiangtan is 0.1°C?0.3°C.In the winter sunny days,Xiangtan and Zhuzhou increased between 0.1°C?0.2°C.(2)In the green-heart planning of the Changsha-Zhuzhou-Xiangtan urban agglomeration,with the increase of the urban land for the green-heart,the wind will slightly shift to the sides of the green-heart when it reaches the green-heart,and return to the initial direction after passing the green-heart,and the wind speed in green-heart is on the downward trend.In the summer sunny days,when the dominant wind is the southerly wind and the southeast wind,the wind speed in the east and south of the Changsha urban area in the downwind direction is reduced by 0.1m·s^-1?0.3m·s^-1.In the winter sunny days,when the dominant wind is the northeast wind,the wind speed in Xiangtan in the downwind direction drops by 0.3m·s^-1?0.5m·s^-1.(3)In the green-heart planning of the Changsha-Zhuzhou-Xiangtan urban agglomeration,in the summer sunny days,when the urban area of the green-heart area is initially expanded,the relative humidity of the green-heart area is reduced,and the relative humidity of parts of Changsha is reduced to within 1.0%.The urban area has further expanded,the relative humidity in the green-heart has decreased,the humidity difference in different regions has decreased,the relative humidity of the surrounding cities has decreased significantly,Zhuzhou has decreased by 2.0%?2.5%,Changsha and Xiangtan both experienced a decline between 1.5%?2.0%.In the winter sunny days,the relative humidity changes are mainly concentrated in the green-heart range,the relative humidity of newly added urban land is significantly reduced,and the relative humidity of Xiangtan is reduced within 0.5%.The urban dry island effect is obvious.In winter sunny days,dry island strength is stronger and lasts longer.(4)In the summer sunny days,when the land use in the green-heart is converted into urban land,the temperature of the mixed land of forest land and cultivated forest land is higher than that of other types of land.The rise in temperature in the surrounding areas of urban land and bare land is higher than other regions.The temperature regulation strategy of adjusting the land use type transformation mode can reduce the temperature of surrounding cities to a certain extent,on this basis,increasing the connectivity of development space inside and outside the green-heart can minimize the influence of the change of land use pattern on the temperature increase of surrounding cities.(5)In the green-heart of the Changsha-Zhuzhou-Xiangtan urban agglomeration,under weak wind conditions,areas with high natural ventilation potential are located in the Xiangjiang area,bare land and cultivated land areas,and in the narrow strip between Xiangtan and Zhuzhou.Adjusting the newly-built urban land,the ventilation corridor construction strategy that connects the areas with better ventilation performance in the dominant wind direction and ensures the connectivity between the green-heart and the external compensation space can increase the wind speed of the urban wind in the downwind direction by 0.1m·s^-1?0.2m·s^-1,the wind speed increase area distribution is mainly affected by the wind direction.In summary,the change of land use pattern under different development scenarios of the Changsha-Zhuzhou-Xiangtan urban agglomeration will have a significant differential impact on the near-surface meteorological elements of the urban agglomeration.Based on that,The proposed green heart planning strategy can provide a powerful reference on the improvement of the atmospheric environment in urban agglomerations and the rational planning of land space.