Intercomparison Of Land-atmosphere Interactions Over Different Surface Types In The Yangtze River Delta

The Yangtze River Delta is located within the typical East Asia monsoon zone.Rapid urbanization,industrialization,and development of agriculture have led to fast and complicated land use and land cover change in this region.LUCC changes the radiation,heat and CO2 fluxes by altering the surface albedo,roughness and Bowen ratio,and finally impacts the micro-meteorological elements.To investigate the land-atmosphere interaction and the climate effect of LUCC in this region where human activities and monsoon climate are highly interactive with each other,we analyze and compare the micro-meteorological elements,surface energy fluxes and CO2 fluxes and different land surface factors based on the data from four sites with different surface types around Nanjing,including urban surface at Dangxiao,suburban surface at Xianling,and grassland and farmland at Lishui County.Then,we also quantify the contribution of land surface factors to the surface temperature differences(ATS)by considering the effects of surface albedo,roughness length,and evaporation respectively,and try to find the dominant surface factor.This study not only fill the observed data gaps of land-atmosphere interaction in this region,but also provide evidence of the numerical simulation and model development.It is shown that there are large differences among different land cover types.Results indicate that(1)the largest differences in daily average surface air temperature(Ta),surface skin temperature(Ts),and relative humidity(RH),which are found during the dry periods between DX-urban and LS-crop,can be up to 3.21?,7.26?,and 22.79%respectively.(2)The differences in radiative fluxes are mainly reflected in upward shortwave radiation(USR)that is related to surface albedo and upward longwave radiation(ULR)that is related to Ts.When comparing four sites,it can be found that both the smallest USR and the largest ULR occur at DX-urban site.(3)The differences in daily average sensible heat(H)and latent heat(LE)between DX-urban and LS-crop are larger than 45 and 95Wm-2,respectively.The proportion of latent heat flux in the net radiation(LE/Rn)keeps increasing with the change of season from the spring to summer.(4)Urban heat island effect results in 2? higher Ta at urban site than other sites in the nighttime.At crop site,LE is dominant due to irrigation and negative H is observed since evaporation cooling leads to low Ts.We analyze the attribution of micro-meteorological element and quantify all the contributions to the surface temperature change(?Ts)at different land cover types.It is found that the cropland cooling effect decreases Ts by-1.76? and urban heat island effect increases Ts by 1.25?.They have opposite impacts but are both significant in this region.Albedo,evaporation,convection and atmospheric background all contribute to ?Ts,and it is the evaporative cooling effect that plays the most important role in this region and accounts for-1.40? of the crop cooling and 2.29 ? of the urban warming.Besides,the background atmospheric circulation is also an indispensable part in land-atmosphere feedback induced by land use change and reinforces both these two effects.