Establishment And Experimentation Of Gravel Parameterization Scheme In Land Surface Model

In this paper,the gravel parameterization scheme is added to the land surface process BCC?AVIM mode(developed by the China National Climate Center)and CLM4.5 mode(developed by the National Atmospheric Center of the United States).Using the measured climate data and soil data from the Maduo station on the Qinghai-Tibet Plateau to discuss the differences between the new and original programs in the simulation of soil temperature and humidity.The impact of different gravel contents on the land surface process was analyzed using the CLM4.5 land surface model.The following conclusions are obtained:(1)Compared with the original plan,the basic parameters of soil water and heat in the new plan have changed significantly.In both modes,the soil hydraulic conductivity increases with the increase of soil water content,and the soil thermal conductivity increases with the increase of soil saturation.The water conductivity and thermal conductivity of the deep layer are greater than those of the shallow layer.Compared with the original scheme,the new scheme increased soil hydraulic conductivity,and the more gravel content,the increase is more obvious.But when the soil water content is very small,the opposite change may occur.The thermal conductivity of the soil is related to the soil water content and the soil thermal property parameters.After changing the basic water and heat parameters of the soil,the changes are more complicated.In the shallow layer,the content of gravel is small,and when the water content is large,the thermal conductivity of the soil decreases in the new scheme,and in the deep layer,the content of gravel is large,and the soil thermal conductivity increases.(2)The new scheme has improved the simulation of soil temperature and humidity in the land surface process BCC?AVIM mode and CLM4.5 model.Especially in CLM4.5,the simulation of the peak value of soil temperature and the valley value of soil water content is obviously improved.It effectively improves the phenomenon that the deep soil temperature simulation is low in the original scheme,and the simulation soil moisture content is low in 80 cm and 160 cm,and the simulation soil moisture content is high in 320 cm.In the land surface process BCC?AVIM model,the new scheme of soil temperature simulation has a better effect in spring simulation,and the soil moisture content in summer and autumn has a better simulation effect.In the land surface process CLM4.5 model,the simulation effect of soil temperature is better in summer and autumn;the simulation effect of soil humidity is better in spring,summer and autumn.The simulation analysis of soil temperature and humidity verified the applicability of the new scheme in the land surface process BCC?AVIM mode and CLM4.5 model,and the new scheme is better than the original scheme.(3)The new scheme was used to study the influence of different gravel content in soil on soil temperature and humidity.The analysis found that the thermal conductivity of the soil increased with the increase of gravel content,which enhanced the endothermic(heat release)of the deep soil in summer(winter).Finally,soil temperature is simulated to increase(decrease).When the soil water content is large(small),the soil hydraulic conductivity increases(decreases)as the gravel content increases,resulting in a decrease(increase)in the simulated soil water content.At the same time,the increase of gravel reduces the simulation of deep soil temperature in winter,turns more water into ice in the deep layer,and further reduces the soil hydraulic conductivity,resulting in the reduction of the simulation of deep soil moisture.Gravel changes the temperature and humidity of the soil,and it will inevitably cause changes in land surface radiation flux and energy flux.The study found that the gravel content increased,the net short-wave radiation decreased,the net long-wave radiation increased in autumn and winter,and weakened in summer,with little change in spring.From late winter to early autumn,the sensible heat flux decreases with increasing gravel content,and increases with increasing gravel content in other months.The change of latent heat flux is more complicated and varies from month to month.The more obvious is that the latent heat flux decreases in spring and increases in summer.The absolute value of soil heat flux increases with increasing gravel content,exothermic heat in the summer half year(positive value),heat absorption in the winter half year(negative value).The overall contribution is that as the gravel content increases,the net soil radiation decreases.