Improvement And Numerical Simulation Of The Runoff Scheme In Land Surface Model

In most widely used land surface models, surface runoff is calculated based onthe simple diagnostic equations, which are too simple take the runoff process intoaccount. This paper put forward a new scheme of the runoff computation aimed atthe lack of the description of the runoff. The modified diffusive-wave equationderived from the Saint-Venant equation was proposed to estimate runoff in BATS,which means that the interaction between the grids was taking into account byintroducing surface slope and roughness. This is a two dimension planar scheme inspatial. The scheme manifests the large-scale advection of the runoff with a specificphysical meaning. It is the important modify than the diagnostic equations before.Then the modified model and the original model are both investigated to simulate thesurface runoff and other physics variable during May to October 1998 in China. Theconclusion as follows:(1) Both the modified model and the original model can simulate the surfacerunoff seasonal variation during May to October 1998, but the runoff of themodified model is much higher than that of the original model and moreclose to the actual values. In the seven month (May to October) gross runoffsimulation, the runoff of the modified model is higher than the climatologicvalue and more closer to the actual values, however the runoff of theoriginal model is much lower than the climatologic level. So the modifiedmodel is better than the original model in the runoff simulation.(2) The simulation of the surface soil volume in modified model is more close tothe actually value than the original scheme. In most of the regions ofChina, the decrease of soil volume is more than 6mm. Because of thewater conservation in the land surface model, when runoff become higher,soil volume will turn low, then soil temperature will increase.(3) The simulation of the surface runoff will not change with topographyresolution.