黄土丘陵区不同降雨格局下土地利用的水土流失效应

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14a径流小区观测数据，依据降雨量．降雨历时和最大30min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。

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

Study on soil and water loss affected by landuse/cover under different rainfall types plays a significant role in soil erosion cont rol 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. Precipita-tion 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 intensi-ties , 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 coefficient s 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 re-lated 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 decrease with time. Soil and water loss is serious in the first several years after plantation , then decreases obviously and get s stable at a lower level. Therefore , more attention should be paid to the different stages of vege2 tation succession.