Study On The Macro-scale Hydrological Model And Its Coupling With The Land Surface Processes Model

Developing and establishing Macro-scale distributed hydrological model are required in order to make certain the regional water and energy cycle, study and resolve the hydrology and water resources problems under the changing environment according to the climatic prediction of GCM.As a branch of hydrologic cycle, land-surface hydrologic processes are nearly relative to atmospheric circle by water and energy exchange between land-surface and atmosphere. Land-surface hydrologic processes are not only the main participants in climate change but are effected by the change. The capacity of understanding and simulating the land-surface hydrological processes in climatic model is the premise to accurate climate prediction. The parameterization of land-surface hydrological processes in present climatic model is quite coarse, and especially the treatment of runoff is too simple. It is needed that the coupling between Macro-scale hydrological model and climatic model for improving the parameterization of land-surface hydrological processes in GCM and the accuracy of GCM prediction.The main contents of research work in this paper are as follows:(1) The development and application of the Macro-scale distributed hydrological model. The Xin'anjiang Model is used as the basic model to develop a monthly grid-based distributed hydrological model for Macro-scale geographic domain. The model is mainly for assessing the effects of climate change on hydrology and water resources. The Huaihe River Basin with the area of 270,000 km2 is selected as the research area. The monthly discharge from 1953 through 1985 is simulated. And the applications have been performed to simulate the effects of climate change on the water resources of Huaihe River Basin.(2) The improvement of grid-based monthly hydrological model. Due to the increase of time interval and decrease of precipitation intensity within a month, no monthly runoff appears in some gridded cells as the Xin'anjiang monthly hydrological model is applied to the Huaihe River Basin. An improved modification in the model is described. As a result, the modified model performs more reasonably in runoffproduction. Two methods of downscaling of monthly precipitation to daily resolution are considered and the model results are compared. The two methods are validated by running the Xin'anjiang model at a daily time step from the monthly data, and the model outputs are more accurate than the monthly hydrological model.(3) The coupling between hydrological model and land surface processes model. The coupling here means that the conception and philosophy of runoff generation and routing scheme in hydrology are introduced to land surface model. The land surface model, which has been coupled to GCM, is the common interface for the coupling between hydrological model and climatic model. The treatment of hydrological processes in land surface scheme AVTM is too rough, and runoff is simply an excess of precipitation over evapotranspiration. The parameterization of runoff generation in AVIM is improved. To represent the heterogeneity of topography, vegetation surface cover and soils, the "storage capacity distribution curve" in the Xin'anjiang model is included in AVIM. In order to evaluate the surface water budgets of AVIM and to evaluate the ability to simulate runoff, the implementation of AVIM to Xilinhe drainage basin (in Mongolia) and daily streamflow simulations from the year 1991 to 1994 are presented. The results of sensitive experiments indicate that runoff will directly affect the change of soil moisture states, thus affect sensible and latent heat fluxes and other energy terms.