The Effect Of Land Use Change On Local Climate And Circulation In Taihu Lake Area

Using the mesoscale model WRF, a series of numerical simulations were performed over the area around Taihu Lake of China. Numerical simulations were firstly carried out to study the local climate response to land use change. Then the local circulation response to land use change were simulated. The simulation results show that:Urbanization is the dominant type of land use change. Net short wave radiation fluxes, ground surface temperatures, and sensitive heat fluxes increase in the urbanized areas, while latent heat fluxes decrease. A decline of wind speed is found in the urbanized areas. Moreover, the lake breeze and urban heat island circulations enhance. Consequently, increased cumulus precipitation occurred in urbanized areas due to the additional vertical velocity, while convection and cumulus precipitation in old town and suburban were inhibited. Stratiform precipitation changes were concentrated in large stratiform rainfall areas. Total precipitation increased in urbanized area and decreased in old town and suburbs, with the proportion of convective precipitation rising. In areas with no land use change, the pattern of precipitation change coincided quite well with the pattern of surface energy flux change.Urbanization makes the old town and suburban temperatures increased slightly during the nighttime, and the highest temperature of old town postponed. The comparative analysis of the diurnal variation of the urban and suburban energy fluxes obtained that urban expansion makes the latent heat flux decreased while sensible heat flux and soil heat flux increases, so the surface temperature and near-surface temperatures rise. There is a clear divergence over Taihu lake in the lower atmosphere. The effect of the urban expansion on low-level vertical velocity distribution is not obvious. There is a convergence of wind vector change around the urbanized area and the larger the city is, the more obvious the convergence is. The vertical velocity of the lake breeze circulation is enhanced by time before entering the city, then suppressed by urban heat island circulation when in the city, and enhanced again and combined with the heat island circulation when reaching the updraft of the heat island circulation. The effect of Urbanization is mainly on urban heat island circulation, and there is no obvious direct impact on the lake breeze circulation.