半干旱黄土丘陵沟壑区降水特征值和下垫面因子影响下的水土流失规律

Mechanism of soil and water loss under rainfall and earth surface characteristics in a semiarid loess hilly area

水土流失是多种因素交互作用的结果，尤其在半干旱黄土丘陵沟壑区更具有典型性。选择定西市安家沟小流域（35°35′N，104°39′E）为典型区域，在其阴坡中部布设了15个径流小区，包括5种土地利用类型（农田、牧草地、灌丛、乔木林、自然草地）和3个坡度（10°、15°、20°），进行径流、侵蚀和降雨前期土壤水分的测定。利用偏相关和方差分析等统计方法，研究了降水特征值及不同下垫面因子对水土流失的影响规律。结果表明，在黄土丘陵沟壑区：①径流量主要受降水量、最大30min雨强、以及降水量与最大30min雨强之积的影响。影响侵蚀量的决定性降水因子为降水量和最大30min雨强的乘积PI30与最大30min雨强，而与降水量、平均雨强的相关性较差；②坡度在10°，20°范围内的变化对径流量没有显著影响，而对侵蚀量有显著影响，在该范围内随着坡度的升高侵蚀量增加（尤以15°-20°范围内增加较快）；③土地利用类型是影响径流侵蚀的一个极其关键的因素。在坡度和土地利用类型双重作用下，以土地利用为主导因素，坡度作用次之。即在一定范围内，人为扰动强烈且坡度高的农田和人工草地最易遭受土壤侵蚀；④径流与侵蚀主要与表层0-20cm的土壤水分呈正相关关系，而与下部其他层次土壤水分无明显相关关系。

Soil and water loss in the semiarid loess hilly area is influenced by many factors, In this study, fifteen experimental plots were established and located on the north-facing hill-slopes of Anjiapo catchment （35°35′ N, 104°39′ E） in Dingxi, Gansu province. Three replications （10°, 15° and 20° slope degree, separately） with the following five land cover types were investigated ： cropland （ Triticum aestivum L. cv Leguan）, pastureland （ Medicago sativa L. ）, shrubland （ Hippophea rhamnoides L. ）, woodland （ Pinus tabulaeformis Carr. ） and grassland （ Stipa bungeana Trin. ） . Surface runoff, erosion amount and initial soil water content were measured. Using partial correlation and analysis of variance （ANOVA）, soil erosion and water losses influenced by rainfall features and earth surface characteristics were studied. Results showed some important facts as follows. Runoff rate has significantly positive relations with rainfall values, maximum 30min rainfall intensity and the product of these two factors. Erosion rate, however, is highly influenced by the product of rainfall and maximum 30min intensity, and has weak correlation with other rainfall features such as rainfall amount and average intensity. Land use type is the most vital factor which could reinforce or weaken the soil erosion and water loss. Slope steepness ranging 10°to 20°contributes nothing on runoff but erosion, and erosion rate increases obviously with slope steepness, especially from 15 degree to 20 degree. In general, cropland and pastureland with higher slope degree and severe human disturbance are very prone to occurrence of runoff and soil erosion. Furthermore, antecedent soil moisture in the surface layer （0 - 20cm） has a more significant positive correlation with rates of runoff and soil erosion than that in other layers.