沙漠化的分形特征研究

在国内外有关学者研究的基础上,运用分形理论研究沙漠化的分形特征。结果表明:①作为风沙地貌形成的物质基础──沙粒,其粒径分布具有分形特征,其分维值的大小差异体现了沙物质分布的区域差异性。②风沙地貌是一种典型的分形几何实体,沙丘分布具有分形特征,其分维值体现了风沙地貌的自相似性规律。③风沙流结构不但是分形,而且是多重分形,其分维值与风速有着极大的关系。④荒漠绿洲景观镶嵌结构具有分形特征,各景观要素的分维值大小代表着该要素镶嵌结构的复杂性和稳定性程度。在黑河流域,自然绿洲的镶嵌结构最具复杂性,也最具稳定性。⑤沙漠化过程具有多重分形特征,如果用降水和风速为标度度量沙漠化过程,都表现出某种不规则性。

Study on Fractal Characters of Desert and Desertification

Applying fractal theories to studies of the distributions of sand diameter and dune, the structures of wind-sand flow and the landscape made from dune, oasis, settlement and so on and to the process of desertification, we get the following findings: (1) There are self-similar characters between the distributions of sand's diameter whose difference in fractal dimension shows the regional difference in the distributions of sands. (2) Dune is a typical kind of fractal geometrical entity and there are self-similar characters between the distributions of dune whose fractal dimension is about 1/2 as much as that of the distributions of sand diameter. (3) The fractal dimension of dune's structure has a better relation with velocity of the wind. As an example of Yanjin region of North Henan province, the fractal dimensions of are 1.9951, 1.8426, 1.6958, 1.7711 and 1.2428 respectively when the velocities of the wind are 6.14 m5s-1, 7.10 m5s-1, 8.70 m5s-1, 9.50 m5s-1 and 10.76 m5s-1 respectively. The structure of dune is both fractal and multi-fractal. (4) The landscape made from desert, oasis, settlement, and so on has the characteristic of fractal. The fractal dimension of each landscape factor shows its complexity and stability. In the Heihe River drainage area in China, the fractal dimension (D) of each landscape factor and the index of stability (SK) are listed in the paper. From the data we know that the complexity and the level of stability of the natural oasis are the highest in all the landscape factors referred in the study. (5) The process of desertification is characterized with multi-fractal feature. And if the level of desertification is measured with precipitation and velocity of the wind, it will bear certain irregularity.