The Improvement Of Surface Hydraulic Process And The Effect On Climate Simulation In China

Surface run-off plays an important role in the hydraulic cycle in the land surface model, which not only controls the soil water content and land-atmosphere water and energy exchange but also effect the sensible heat or latent heat flux. However, in most widely used land surface models, it is calculated based on the simple diagnostic equations, which are too simple take the runoff process into account. But the runoff have a very complex mechanism, because the simple Horton runoff and Dunne runoff are rarely in the natural runoff. There are very complex combination in the two mechanism of runoff process. This decided by the topography, soil, geology, vegetation and climate condition ,etc. If less consider one of the factors above , it would result in the less or more estimate of the runoff, then result the energy computed wrong.This paper put forward a new scheme of the runoff computation aimed at the lack of the description of the runoff.The modified dynamic-wave equation derived from the Manning equation was proposed to estimate run-off in BATS, which means that the interaction between the grids was taking into account by introducing surface slope and roughness. This is a planar scheme in spatial. The scheme manifest the large-scale advection of the runoff with a specific physical meaning. It is the important modify than the diagnostic equations before.We adopt the spatial difference method to solute the difference equation. After this modification, simulations were carried out by coupling BATS into Regcm2. The outputs of the simulation were compared to the ground measurements. we adopt T106 data in 1998 June-October to simulate in the mostly China . After 3 months continuous run , we get some output of the model .By analysis the output of the model ,such as runoff , precipitation , temperature, etc . The result shows the outputs of modified model agree better than those of the original model, such as precipitation and air temperature. Theconclusion as follow:At first , the runoff of the modified model is 10 times than the original model . This result of S2 scheme is close to the data of ECMWF . The runoff centre is also close to the data of ECMWF.Secondly ,the simulation of the temperature in modified model is more closed to the actually temperature than the original scheme. In most of the regions of China , the increase of temperature is more than 0.5 ℃, the error of the modified model is less than the original model by 0.2 ℃ . In the 3 stations of China (Wuhan , Nanjing , Yichang), the situation is more better than the original model also . So we conclude that the modified model is better than the original model in the temperature simulation.At last, we analysis the course of this climate change. We find that the increase of the runoff lead to the soil moisture decrease. Then the evaporation is less than the original model.