降水-植被耦合关系及其对黄土高原侵蚀的影响

降水、植被与侵蚀过程三者之间关系的研究，是地表过程领域中重要的科学问题，迄今未能完全解决。通过对黄土高原地区大量实测资料的分析，揭示了森林覆盖率和降雨侵蚀力随年降水量的非线性变化。发现了森林覆盖率随年降水变化过程中的临界点，即当年降水小于450 mm时，森林覆盖率很小且基本上不随年降水而变化；当年降水大于450 mm以后，森林覆盖率随年降水的增大而急剧增大。同时还发现，降雨侵蚀力随年降水量的变化过程也存在着两个临界点。当年降水量小于300 mm时，降雨侵蚀力很小且基本上不随年降水而变化；当年降水量超过300 mm时，降雨侵蚀力随年降水量的增大而迅速增大；当年降水量大于530 mm以后，降雨侵蚀力随年降水量增大的速率进一步加大。从分析与上述各临界点相联系的植被抗蚀力和降雨侵蚀力的对比关系入手，解释了黄土高原地区侵蚀强度随年降水变化的非线性图形，即随年降水的增大，侵蚀强度先是增大并达到峰值，然后再减小。并讨论了上述各个临界点对于黄土高原侵蚀治理的应用意义。

Coupling Relationship between Precipitation and Vegetation and the Implications in Erosion on the Loess Plateau, China

The relationship among precipitation, vegetation and erosion is an important, unsolved issue in the field of earth surface processes. Based on data from the Loess Plateau of China, some nonlinear relationships between forest cover (Cf), rainfall erosivity (Ir) and annual precipitation (Pm) has been found. A threshold has been identified at Pm = 450 mm, that is, when Pm is smaller than 450 mm, Cf is low and basically does not vary with Pm; when Pm exceeds 450 mm, Cf increases rapidly. Furthermore, two thresholds are identified in the relationship between rainfall erosivity and annual precipitation. When Pm is smaller than 300 mm, Ir is low and basically does not vary with Pm. When Pm exceeds 300 mm, Ir increases rapidly; when Pm becomes larger than 530 mm, the rate at which Ir increases with Pm becomes higher. Based on these nonlinear relationships, the nonlinear picture of variation between erosion intensity and annual precipitation, i.e., the erosion intensity increases with annual precipitation to a peak and then declines, is explained. The implication of these thresholds for erosion control on the Loess Plateau is discussed.