可用于陆面过程模型的地形指数水文模型中简化参数化方案的研究

A study of simplification of some schemes in the TOPMODEL for use in land surface models.

在全球气候系统模型中,陆面水文过程对提高模拟精度有显著作用。土壤水分空间非均匀分布对于蒸发和径流的计算以及能量在潜热和感热之间的分配具有重要的影响,但现有的多数陆面过程模式未能考虑土壤水分水平非均匀性的影响。地形指数模型以其较好的物理基础、参数少、计算量小,且能考虑地形变化对土壤水分非均匀分布影响等优点,使其有潜力模拟陆面过程中水分过程分布非均匀二维特性。目前地形指数水文模型已被推荐应用于陆面过程模式(Land surface models,LSMs)中以改进对陆面水文过程的模拟能力。在地形指数模型中,数据的空间分辨率、河道的起始临界值、非饱和区域的分区和空间各点的坡度等因子不同的确定,都能对模拟结果产生重要影响,对它们如何合理地给定,既不降低模型精度,又能省时、省资源是十分重要的。本研究通过大量的敏感性模拟试验,较系统地探讨上述参数不同的确定方案对流域水量平衡模拟结果的影响。主要结论有:(1)将流域按地形指数值大小分为16块与仅区分饱和区与非饱和区或仅区分饱和区、较湿润区和较干区3块模拟结果相差不大,因此将地形指数模型应用于陆面模式时仅区分饱和区与非饱和区或区分饱和区、较湿润区和较干区3块这种简化方案也许是一种可行的选择;(2)不考虑坡度会扭曲水量平衡各要素的计算,用一个平均坡度替代实际坡度的办法就会有比较接近了实际坡度的结果。因此,LSM模型中一维均匀的网格做法应该改进,但太细致的坡度取法也许没必要。以上结论可为今后发展用于陆面模式的大尺度水文模型提供依据。

Hydrological processes play an important role in the improvement of climate system model.The spatial heterogeneous distribution of soil moisture content has a great influence on calculated evaporation and runoff as well as surface energy partition into latent and sensible heats.However,most of currently used land surface models（LSMs） are not able to take into consideration the influence of the heterogeneous distribution of soil moisture.The topographic index model（TOPMODEL） is a physics-based model with a few parameters, less computer resources required and the capacity of taking into consideration the effect of topography on heterogeneous distribution of soil moisture by which the model is capable of dealing with the heterogeneous hydrological process of two dimensional characteristics in a land surface model.This index model has been recommended for use in current LSMs to improve the simulation skill of hydrological process on land surface.When the TOPMODEL is used for numerical studies,there could be different setting or selection for some parameters in several schemes therein such as spatial resolution of data base,Channel Initiation Threshold（CIT）,division of unsaturated areas in a catchment and spatial distribution of land surface slope,which will have important effect on the model simulated results.The way how to set the parameters in these schemes reasonably with no accuracy losing and reducing the requirement to the data and computer resources is very critical.In this study,a detailed numerical study of the schemes in the model has been conducted with the result that the effect of different setting for the schemes on the simulation outcomes of water balance in a catchment is revealed.The main conclusions from the study are as follows：（1）the simulated results of the case with the catchment being divided into 16 parts according to topographic index values are closer to those of the case with catchment being divided into only two（saturated and unsaturated parts） or three（saturated,wetter and drier parts） parts.So,when the TOPMPDEL is applied to LSMs,it may be a reasonable simplification to divide catchment into two（saturated and unsaturated parts） or three（saturated,wetter and drier parts） parts;（2） It is found from the study that the simulation outcome of water balance will be distorted if the effect of slope for the catchment is ignored completely;however,the simulated result of water balance for the catchment with one mean-slope given are closer to the result of water balance for the catchment with real spatial distributed slope set,suggesting that the way used in the current LSMs considering the grid as the one-dimensional-homogeneous should be improved,and,on the other hand,considering topographic slope information in very detailed way may not be necessary.All the results provide the useful information for the development of a simplified and reasonably accurate hydrological model for use in a land surface model.