| Water is not only the main driving force and carrier of matter driving the mass & energy circulation in the SVATs (Soil Vegetation Atmospheric Transfer Schemes), but also the important tie that links the temporal and spatial variations of atmosphere, ecology, hydrology and human activities in the earth system. Due to the global climate warming and the great negative affections caused by human activities, the hydrological cycle on the earth has undergone enormous changes since the twentieth century. Some extreme climate and hydrological diaster events, such as drought and flood occurs frequently, the temporal and spatial distributions of the water resources become more and more abnormal. And these changes might directly impact on the sustainable development of the production as well as the living environment and the social economy of human beings. In a word, we are facing the great challenge from the changing earth.During the last two decades the land-surface hydrological processes were regarded as one of the important contents on global change research by International Geosphere Biosphere Project (IGBP), World Climate Research Program (WCRP), Global Energy and Water cycle Experiment (GEWEX). In these projects and programs, many researches on simulating the land-surface hydrological process and its coupling studies with climate models have been performed. As a hot topic in the global change studies, how to develop a new land-surface hydrological model that could both describe the temporal and spatial variations of hydrological cycle effectively and assess water resources partitioning quantitatively within regional or glocal scale, have drawn great interests of scientists. Once such land-surface hydrological model could be effectively coupled with regional climate model with higher resolution, thus it would be possible to drive the hydrological model with the scenario fields provided by climate model to simulate and explain the response of hydrosphere under possible climate change scenarios. The study and development of such modeling system, therefore, is of great importance for forecasting and early warning of the extreme climate and hydrological events.In the present circumstances, an effective and operational way might be to develop a simple regional hydrological model with the improved land-surface hydrological processes parameterization scheme which can both express the topographic information and describe the bidimensional characterics of hydrological processes in landsurface-atmosphere interactions. For acheieving such purpose, based on the saturated runoff generation mechanism of the improved SIMTOP with topography concept (TOP), in association with the water budget calculation principle of the Xinanjiang model (X), a land-surface hydrological model entitled as TOPX, which is able to better capture the main features of hydrological processes and describe the inner mechanism of hydrology cycle in regional scale by applying high resolution topographic information to course resolution regional hydrological simulations with the linear scaling transfer scheme, was attempted. TOPX was designed to be coupled with regional climate model RIEMS to improve the parameterization scheme of the hydrological processes in regional climate model. Thus this attempt opens a way to use high resolution topographic information and TOPMODEL concepts to be used in the land-surface process modeling for regional scale applications.To achieve the final goal of the research, four initial problems as listed below must be solved in the course of study:.(1). How to compute the topographic index more theortically and accurately which can be utilized universally and operational: Development a new algorithm named as IMFD.On the basis of brief introduce on fundamental theory of FD8-Quinn, An algorithm accurately calculates the effective contour length in the accumulated flow partitioning involved in ln(α/tanβ) computation by using internal tangent circle on conical surface method and meanwhile it accounts for rational computation of ln(α/tanβ) in calculation of the cumulative upslope source areaα, named as IMFD, was proposed. In order to further investigate the computing accuracy and detect the effectiveness of the algorithm, quantitative comparision of the errors generated by MFD-Quinn and IMFD was conducted. Some standard and artificial topography constructed with mathematical models and the'real-world'DEMs are used to evaluate IMFD algorithm quantitatively.(2). How to determine a universal scheme to address the scaling issues involved in topographic indexes derived from different resolution DEMs in the whole territory of China.With IMFD, statistic analyses were made to the mean values of topographic indexes computed from two resolution DEMs (90-m×90-m and 1000-m×1000-m spatial resolution respectively). All the 100 selected DEM blocks in three different sizes (1°×1°, 0.5°×0.5°and 0.1°×0.1°respectively) evenly sampled in the whole territory of China were carefully examined, the linear scaling transferring schemes were obtained. In order to further examine the validity of the downscaling scheme, the sampling density is increased in the central part of China. Experimental results suggested that these linear scaling transferring schemes are reliable and are geographical location and topography independent.(3). How to construct an effective lanf-surface hydrological model to be easily and effectively coupled to regional climate model RIEMS.In this paper, a simple but effective method, named as two-parameter exponential function, was developed to represent the spatial distribution regime of topographic index accurately and simply. Thus the topographic parameters were ingeniously linked with the saturated runoff generation mechanism of the improved SIMTOP with topography concept (TOP), in association with the water budget calculation principle of the Xinanjiang model (X), a land-surface hydrological model entitled as TOPX, which is able to better capture the main features of hydrological processes and describe the inner mechanism of hydrology cycle in regional scale by applying high resolution topographic information to course resolution regional hydrological simulations with the linear scaling transfer scheme, was developed.This new model was firstly tested in You Shuijie catchment located at humid Hanjiang basin and in Malian River catchemet located at semi-arid loess platean in single-point offline simulations. The experimental results suggested that the TOPX is able to give quite satisfied performance in daily runoff as well as hydrological processes simulations. It is wealthwhile to mention that TOPX is not only capable of capturing the temporal and spatial variations of various hydrological processes accurately, but is also able to be used in both semi-arid and humid area hydrological simulations with outstanding performances.(4). How to effectively couple TOPX model with regional climate model RIEMS.The TOPX was developed for coupling with regional climate model, one of its notable characteristics is to consider the topographic effect in land-surface hydrological processes, and also account for the process of the hillslope flow concentration within calculating grids and the process of the river flow concentration between grids, by applying high resolution topographic information to course resolution regional hydrological simulations with the linear scaling transfer scheme the TOPX was coupled with RIEMS successfully. Using this coupled model (RIEMS+TOPX), simulation of the daily runoff from1989 to 1999 at Zhang Jiashan, the hydrological gauge of the Jinhe Watershed were experientally carried out, the satisfied performances of the coupling system compared with the orginal RIEMS were demonstrated. Three floods of 1990 simulated by RIEMS+TOPX and the temporal and spatial variations of their corresponding daily rainfall were investigated to evaluate the performance of the system. It was found that the rainfall predicted by RIEMS is the most sensative parameter that gonvers accuracy of the runoff simulated by RIEMS+TOPX.Through this study, the conclusions can be summaried as follows:①Compared with the multiple flow direction algorithm (FD8-Quinn), the new algorithm IMFD is more accurate to express the relationship of upslope contribution area and soil water content in real watersheds and so as to reflect the hydrological similarity of real catchments more accurately.②The linear scaling transfer relations on topographic index in different spatial resolutions for the whole territory of China established in this study is reliable and can be easily applied in the topography-based land-surface hydrological simulations.③Based on the saturated runoff generation mechanism of the improved SIMTOP, in association with the water budget calculation principle of the Xinanjiang model, a land-surface hydrological model entitled as TOPX, which is able to better capture the main features of hydrological processes and describe the inner mechanism of hydrology cycle in regional scale by applying high resolution topographic information to course resolution regional hydrological simulations with the linear scaling transfer scheme, was successfully developed.④RIEMS coupled with TOPX largely improve the numerical simulation ability of the regional climate model on land-surface hydrological processes studies. RIEMS coupled with TOPX has great potential for regional daily runoff forcastings.The development of land-surface hydrological model TOPX and its coupling research with regional climate model RIEMS largely improve the numerical simulating ability on land-surface hydrological processes of regional climate models. This study is very significant for revealing the interactions and influencing mechanism of climate, ecology, hydrology and environment both in theory and in applications. Key words: Land-surface hydrological processes; regional climate model;...
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