黄土高原侵蚀产沙强度的时空变化特征

Temporal and Spatial Variation Features of Sediment Yield Intensity on Loess Plateau

采用“水文—地貌法”即水文站实测值与侵蚀形态类型相结合的方法，将黄土高原划分为２９２个侵蚀产沙单元，分别对治理前后侵蚀产沙强度的时空变化特征进行了分析。结果表明：黄土高原自７０年代以来，由于降雨因素和水土保持作用的影响，侵蚀产沙强度的结构特征发生了明显变化，侵蚀模数＞１００００ｔ／Ｋｍ２．ａ的极强烈以上的侵蚀面积急剧减少（减幅７１．８％），减沙幅度最大的区域主要分布在以无定河为中心的极强烈侵蚀区和汾河流域的大部分地区（减幅５０％以上）；黄土高原侵蚀产沙，按流域区段主要来自河龙区间（５４．８％），按类型区主要来自黄土峁状丘陵沟壑区（２７．４％）和干旱黄土丘陵沟壑区（２３．１％），按侵蚀带主要来自暖温带半干旱草原风蚀、水力侵蚀带（３４．８％）和暖温带半干旱森林草原水力侵蚀带（３２．６％；以侵蚀模数＞１００００ｔ／Ｋｍ２．ａ作为标准，可将黄土高原划分为７个极强烈以上的侵蚀产沙中心，其面积虽仅占全区总面积的１５．５％，但其产沙量却占到全区总产沙量的４２．１％。

Based on the distribution of the hydrological station and it's observation series of sediment information on loess Plateau, the study area was divided into 120 hydrological control area firstly, then according to the different soil erosion type area, the 120 hydrological control area were divided into 292 soil erosion units. The main results are as following: (1) The sediment yield of loess plateau (average condition from 1955 to 1989) are mainly come from the violence erosive area with erosion modulus >5000t/km2.a, the area of it made up 42.8% of the total sediment yielding area, and the sediment from it amounted to 85.0% of the total amount of erosive sediment yield. And the mighty violence erosive area with erosion modulus >10000t/km2.a, the area of it only made up 18.4% of the total sediment yielding area, but the sediment from it amounted to 50% of the total amount of erosive sediment yield. In the 8 grade of erosion intensity, the sediment yield from the area with erosion modulus2500-15000t/km2.a amounted to about 90% of the total amount of erosive sediment yield, and the sediment from the area with erosion modulus 10000-15000t/km2.a reach 35.0%. (2) Sediment intensities have changed evidently because of rainfall factor and the effects of soil and water conservation. From the view of structural features of sediment area, the sediment area with erosion modulus > 10000t/km2.a reduced rapidly, from 8.7 × 104km2 (1955-1969)to 2.5 × 104km2 (1970-1989), reduced 71.8%, and the proportion in the total area decreased from 28.2% to 7.9%. And the sediment area with erosion modulus >15000t/km2.a reduced from 2.9 × 104km2 to 0.6 × 104km2 , reduced 78.3%; the area with erosion modulus >20000t/km2.a reduced from 1.0×104km2 to only 0.2×104km2 , reduced 81.0%. In the 8 grade of erosion intensity, the sediment area with erosion modulus >20000t/km2.a , 15000-20000 t/km2.a and 10000-15000 t/km2.a decreased greatly , and the reductive degree is 81.0% ,76.9% and 68.7% respectively. And from the view of structural features of sediment yield, the proportion of sediment yield of mighty violence erosive area with erosion modulus >10000t/km2.a in that of total area reduced from 66.0% to 27.8%. And sediment yield reduced more greatly is the area with erosion modulus >20000t/km2.a , 15000-20000 t/km2.a and 10000-15000 t/km2.a, the reductive degree is 77.1%, 76.7% and 71.6% respectively. (3) The regions where the sediment yield reduced evidently are mainly distributed in the mighty violence erosive area surrounding Wuding River, and the majority of Fen river, the reductive degree is above 50%. Before soil and water conservation (1955-1969), the regions with erosion modulus >10000t/km2.a were distributed in the majority of the mainstream reaches of Yellow River between Hekouzheng and Longmen area, the upper reaches of Beiluo River, the most part of upper and middle reaches of Jing River, and the much area of Hulu River and Sandu River in Wei River basin. After soil and water conservation (1970-1989), the regions with erosion modulus > 10000t/km2.a were scattered in Huangpuchuan river, the lower reaches of Kuye River, Jialu River, Wuding River and Qiushui River near to the mainstream reaches of Yellow River, and the overhead of Beiluo River and Jing River. After control, the area with erosion modulus > 10000t/km2.a in Hekouzheng - Longmen area, the upper reaches of Jing River and Wei River decreased on a large scale, and the erosion modulus reduced to 5000-10000 t/km2.a. the area with <5000 t/km2.a has changed not too much. (4) The sediment yield of loess plateau, calculated according to tributaries, are mainly come from Hekouzheng - Longmen area (54.8%), next from Jing River (17.6%) and Wei River (13.3%); according to soil erosion type areas, are mainly from loess Mao hill gully region and arid loess hill gully region (50.5%), next from loess Liang hill gully region (11.0%), loess flat hillock hill gully region (9.8%), and loess plateau hill gully region (9.7%); according to soil erosion belts, are mainly from wind and water erosion belt i