Research On The Influence Of Grassland Underground Biomass Parameterization On Land Surface Process Simulation

The root physical process plays an important role in surface energy balance and water cycle.At present,the influence of Parameterization Schemes of underground biomass on the simulation of land surface processes in the alpine grassland is not clear.To explore the influence of parameterization schemes,and to provide reference for establishing root parameterization schemes of land surface process model in the future.In this paper,using Maqu station observation data to drive the Beijing Climate Center Land Model(BCC_AVIM),and introduce different parameterization schemes of root water uptake process to simulate.Improving the parameterization scheme of root related parameters,to design sensitivity tests by BCC_AVIM,GFOALS and BCC_CSM model.Compare the differences between the simulation results of different parameterization schemes in the Qinghai-Tibet Plateau.The main achievements are as follows:(1)The root water uptake process parameterization scheme is divided into root distribution model and soil water availability function for root.The modification of relevant parameterization schemes directly affects soil temperature and soil water content.The comparison results show different parameterization schemes have a greater impact on sensible heat flux and latent heat flux,especially canopy transpiration.Sensible heat flux is mainly affected by the corresponding temperature,latent heat flux is correlated with soil water content and temperature.(2)The difference in simulation is affected by precipitation.During the rainy period,the root distribution model comparison schemes simulation is more sensitive,there is a big difference between the sensible heat and latent heat flux simulated by the original model.During the less rainy period,the soil water availability function for root comparison schemes simulation is more sensitive,there is a big difference between the sensible heat and latent heat flux simulated by the original model.(3)Soil thermal conductivity is related to soil porosity.The thermal conductivity decreases with the increase of porosity.The simulated soil temperature after the improved scheme is on the high side.In rainy season,the thermal conductivity of water is higher than that of air,which results in the low simulated soil temperature.The simulated difference value of soil temperature is positively correlated with sensible heat flux and negatively correlated with latent heat flux.(4)Through sensitivity tests,it was found that the root hydrological effects of alpine grassland had a significant impact on surface temperature,humidity,surface radiation budget and energy distribution.Changing the parameterization scheme willdirectly affect soil water content.In the areas with low simulated soil water content,the simulated temperature is higher.Because of the decrease of moisture and the increase of temperature,the transpiration of vegetation decreases and latent heat flux decreases.Water absorbs more solar radiation than soil,so the simulation of net radiation is higher in the areas with low soil moisture content.(5)In the simulation of coupled climate model BCC_CSM,the change of soil temperature is the most sensitive among the changes of temperature parameters.Because of the special topography of high altitude in the west of Qinghai-Tibet Plateau,the original positive correlation between soil temperature and surface sensible heat flux is not significant.At this time,the influence of soil liquid water content on sensible heat flux is dominant,and the thermal conductivity of water is greater than that of air.The soil liquid water content will affect the heat exchange between ground and air in this area.The above results can provide some reference for further improving the parameterization scheme of grassland underground biomass.