黄土丘陵区不同降雨格局下土地利用的水土流失效应

Soil and Water Loss Affected by Landuse Under Different Rainfall Patterns in the Semi-arid Loess Hilly Area

研究不同类型降雨事件下土地利用/覆被对水土流失过程的影响,对于科学指导植被建设和控制水土流失具有重要意义。基于14 a径流小区观测数据,依据降雨量、降雨历时和最大30 min雨强3个指标,利用快速聚类的方法将定西市安家沟内产流性降雨事件划分为3种格局。总体而言,降雨格局2为雨量集中、雨强很高而历时较短的降雨事件的集合;降雨格局3为雨量分散、雨强小而历时很长的一类降雨事件的集合;而降雨格局1则为雨强、历时等特征值都介于格局3和格局2之间的降雨事件的集合体。在此基础上,着重研究了5种土地利用类型在不同降雨格局下的径流侵蚀规律。(1)从静态观点来看,5种土地利用类型抵抗径流侵蚀的能力依次为沙棘>荒草>油松>苜蓿>小麦。苜蓿地的土壤侵蚀严重,可能跟人为干扰破坏和苜蓿自身生长习性有关。(2)3种降雨格局中,以降雨格局2下各土地利用类型的径流侵蚀最为严重,降雨格局1次之,降雨格局3最弱。即雨量集中、雨强很高而历时较短的降雨类型是影响该地区水土流失的主导因素。(3)多年生植被(如沙棘、油松等)的径流侵蚀有随生长年数增长而减弱的趋势,以生长初期最为严重,随后逐渐减弱并稳定在一个较低的水平上。因而认为,不同土地利用类型下的径流侵蚀不仅取决于该植被类型,更重要的是决定于该植被所处的生长发育阶段。

Study on soil and water loss affected by landuse/cover under different rainfall types plays a significant role in soil erosion control and vegetation restoration, which can give scientific guidance to the practice. Based on 14 years of measurements in the experimental hydrologic plots, different rainfall patterns were classified. Precipitation amount, duration and maximum 30 min intensity were selected as the comprehensive index to divide the local rainfall events into three different patterns. Generally, pattern 1 is the aggregation of those with medium intensities, durations and amounts. Pattern 2 is the aggregation of rainfall events with such features as high intensities and short durations. Pattern 3 is the aggregation of those with low intensities and long durations. Accordingly, runoff and erosion features of five landuse types governed by these three rainfall patterns, as well as their features in different years, are all stressed. The main results are shown as follows. Firstly, from the static point of view, the lands characterized by the mean runoff coefficients and mean erosion moduli are in the order of seabuckthorn〉 natural grass 〉 Chinese Pine 〉 alfalfa 〉 wheat. The reason why alfalfa land has severe runoff and erosion may be related to its growing characteristics and human disturbance. Secondly, runoff and erosion under rainfall pattern 2 hold the most serious position, followed by pattern 1 and pattern 3. This means that rainfall events with high in-tensities and shorter durations play dominant roles in causing soil and water loss in the semiarid area. Lastly, perennial plants such as seabuckthorn and Chinese pine show a very clear trend that runoff coefficients and erosion modulus deerease with time. Soil and water loss is serious in the first several years after plantation, then deereases obviously and gets stable at a lower level. Therefore, more attention should be paid to the different stages of vegetation succession.