土地利用变化对城市气象环境影响的数值研究

Simulation of the Land-use Change Effect on Urban Meteorological Environment

采用南京大学的三维非静力区域边界层模式,选取典型天气状况作为代表,对北京1980、1990、2000及2004年不同土地利用类型冬夏两季的城市边界层特征进行数值模拟,结果表明:城市土地利用状况的改变对边界层热力及动力结构产生显著的影响,这种影响在夏季个例的日间尤为明显.如,由于建筑储热能力变化,地表反照率变化,导致城市表能量平衡重新分配,1980年个例较之2004年个例,夏季城市区域平均净辐射通量增加160 W.m-2.城市植被覆盖率减小,地表湿度降低,使得潜热通量最大减小81 W.m-2,感热通量则最大增加146 W.m-2.热通量和动量通量增大,地气相互作用的加剧,夏季城市区域气温增幅最大达2.2℃.建筑物高度及密度增大,湍能增强,且影响高度增大,混合层高度增加,使水汽等物质输送加强,分布更加均匀.城市动力粗糙度增加引起的阻尼作用在风速大时较明显,北京冬季日间风速较大,风速减少最大可达2.02 m.s-1;然而冬季大气层结较为稳定,湍能发展受到抑制,湍能及通量输送的变化不如夏季个例明显;地表较为干燥、植被覆盖稀少,潜热减小及感热增加的变化幅度较小,增温变化也不如夏季个例明显.

With a three-dimensional, non-hydrostatic regional boundary layer model （NJU-RBLM）, some numerical experiments are employed to investigate the impact of land-use change on local meteorological environment including the urban boundary layer （UBL） structure. The land cover of Beijing city in 1980, 1990, 2000 and 2004 and meteorological conditions in the summers and winters are taken as examples. The simulation results show that land-use change has a great effect on the thermal and dynamical structure of the UBI. structure, particularly in the daytime of summer. For example, firstly, the surface energy balance is broken down and redistributed by surface characteristic change. In the daytime of summer, net radiation in urban region inereases with a maximum of 160 W/m^2 from 1980 to 2004 due to the changes of surface albedo. Decrease of vegetation cover and surface moisture may lead to reduction of latent heat, which causes increase of sensible heat with a peak of 146 W/m^2. Secondly, the momentum and heat fluxes increase, and the exchange between the ground and atmosphere strengthens as well. As the result, near-surface temperature in urban region has a maximum increment of 2. 2 ℃ at 14 ： 00 in summer. Thirdly, with more buildings, stronger turbulent kinetic energy （TKE） higher momentum flux and heat flux, surface energy and moisture will be transported up and mixed strongly, and the mixed layer depth rises with 400 m at 14 ： 00 in summer. The increase of buildings weakens the wind and leads to the convergence of airflow in the lower layer of atmosphere. The attenuation of wind is more significant when the wind speed is greater in the lower layer. In winter, the wind speed in the daytime is greater, and the reduction of wind can reach 2.02 m/s at 14 ： 00 between 1980 and 2004 in winters. The decrease of the wind speed usually results in the strengthening of TKE and the greater turbulent transportation, while the stable stratification suppresses the development of turbulence, the variation of turbulence and the exchanges of energy and moisture in winter are not larger than those in summer. On other hand, there are less the vegetation and surface moisture and the deduction of latent heat and the increase of sensible heat are not as big as those in summer.