Numerical Simulations Of Regional Climatic Effects Of Land Use And Land Cover Change

Land use and land cover change(LUCC),one of the significant human activities,is a major cause affecting the global and regional climate change in recent hundred years.In this thesis,sensitivity experiments on impacts of large-scale land use change on surface energy balance,hydrological cycle and atmospheric circulation were conducted.Note that global warming is a hot topic,the importance of climatological background to LUCC were investigated.Also,future LUCC in determining the climate changes was explored.In addition,impacts of LUCC on regional climate over East Asia were analyzed.Main conclusions are as follows.(1)The NCAR Community Atmosphere Model(CAM4.0)was used to investigate the climate effects of LUCC.Two simulations,one with potential land cover without significant human intervention and the other with current land use,were conducted.Results show that the impacts of LUCC on diurnal temperature range(DTR)are significant.In general,the LUCC significantly controls the DTR change through the changes in vegetation transpiration and canopy evaporation.The effects of LUCC on surface energy and water cycle are not only associated with the underlying physical characteristics,but also tied to the atmospheric circulation.(2)Considering the interannual forcing of these two factors(the greenhouse gas concentrations and land use changes),the NCAR Community Atmosphere Model(CAM4.0)was used in this study to investigate the importance of climatological background to LUCC impacts.Experiments based on the difference in the background climate,the greenhouse gas concentrations in 1850 and in the present age indicate contrary changes in climate sensitivity through estimations of the radiative forcing associated with LUCC.Therefore,the background climate appears to play an important role in the regional impact of LUCC,especially at higher latitudes.In addition,global warming predominantly influences snow-albedo feedback in the mid-latitudes,thus determining the impact of LUCC,whereas the regional difference in precipitation caused by global warming is responsible for the differing climate response to LUCC in the tropics and subtropics.(3)To demonstrate the importance of LUCC on future climate projections,we present an analysis of the climatic effects of future LUCC based on the simulations of the second generation Earth System Model of the Canadian Centre for Climate Modelling and Analysis(CanESM2).The simulated results show that the albedo effect dominates in the mid-latitudes.While in the tropics,LUCC lead to a warming effect and an increase in precipitation primarily because of the reduction in the roughness length.Due to LUCC,future global land use emissions are approximately 35.7 Pg C(32.1 Pg C)in RCP2.6(RCP8.5)scenario.When compared to the greenhouse gas(GHG)and aerosol influences,the land-atmosphere CO2 fluxes can be regionally modulated by LUCC effects when compared with the effects of GHG/aerosol forcings.The results presented here highlight the need to understand the response of the land surface carbon cycle due to LUCC effects over a long period of time.(4)The Regional Climate Model(RegCM4.1.1)was used to investigate the climate effects of LUCC over East China.Results show that temperature responses due to LUCC are significant in summer.LUCC tend to cause stronger Indian southwest monsoon and South China Sea monsoon,and the Subtropical High goes southward,the precipitation belt tends to be in south China.For the impacts of future LUCC,intertropical convergence zone(ITCZ)strengthens and goes northward,the summer precipitation belts locate in South of China and Northern China.In addition,Subtropical High goes southward which is adverse to the formation of precipitation.For winter,the wind changes due to LUCC are local independence,and the winter monsoon is not significant over East Aisa.