Sensitivity Tests And Improvements Of Canopy Interception Simulation Based On CLM4.5

As an essential land cover type,vegetation plays a significant role in the land-atmosphere system.Further exploring the effects of vegetation on the global water and energy cycles will help us fathom the land-atmosphere interactions.Based on the sensitivity tests in the NCAR's Community Land Model(CLM4.5),this thesis evaluates the significances of canopy interception on climate simulations.Three datasets are used to evaluate canopy evaporation,evapotranspiration and latent heat flux within the CLM4.5 default canopy interception scheme.To solve the problems in the current scheme,four improved schemes are proposed to take canopy structure and meteorological factors into consideration.The new schemes will also influence the water and energy cycles.The main conclusions are as follows.(1)Canopy interception influences hydrology,climate and vegetation growth.The changes of canopy interception can cause the global average canopy evaporation,transpiration,evapotranspiration,and runoff over land areas to vary 154.5%,24.6%,8.6%and 14.5%,respectively.Meanwhile,the terrestrial average 2m temperature varies 0.25? globally and 1?in tropics.The variation of interception affects terrestrial and marine rainfall in tropics and local precipitation in mid-high latitude forests through the regulating effect of evapotranspiration on surface thermal distribution and atmospheric circulation.Additionally,interception also links to vegetation's photosynthesis,which depends on vegetation types.(2)The patterns of biases in canopy evaporation,evapotranspiration and latent heat flux in the CLM4.5 are similar.There are apparent negative deviations in tropical rainforest and boreal forests,positive deviations in tropical grassland,India Peninsula and northern Australia,and positive bias in islands and coasts.The bias from canopy evaporation contributes to the simulation errors in evapotranspiration and latent heat.(3)The improvement schemes use the measured canopy storage capacities for different types of vegetation and add the wind-induced and the rainfall-intensity-induced interception processes to the CLM.As a result,the improvement schemes improve the simulations of canopy evaporation,evapotranspiration and latent heat flux in the forest areas on the global scale.And the pCWle and pCWlo schemes apparently improve the simulations in deciduous forest areas,coasts,and islands.It also shows that the selection of the canopy interception scheme apparently affects the simulations of terrestrial water and energy cycles.