长江上游流域降雨侵蚀力变化对河流输沙量的影响

利用长江上游主要水文站1956~2010年输沙量数据和雨量站日降雨量时间序列资料,采用线性回归研究流域降雨侵蚀力与河流输沙量的关系,并估算长江上游各子流域降雨侵蚀力变化对河流输沙量的总体贡献。结果表明:长江上游降雨侵蚀力为2 362 MJ·mm/(hm²·h·a)到3 814 MJ·mm/(hm²·h·a),多年平均值为3 006 MJ·mm/(hm²·h·a);各子流域的年均降雨侵蚀力差异较大,其中乌江子流域最大,为5 055 MJ·mm/(hm²·h·a),金沙江子流域最小(1 560 MJ·mm/(hm²·h·a)),不足乌江子流域的1/3。各子流域降雨侵蚀力的极值比大小嘉陵江 > 岷江 > 乌江 > 金沙江。长江上游流域以及子流域输沙量在1956~2010年间均呈总体下降趋势,各子流域年均输沙量大小金沙江 > 嘉陵江 > 岷江 > 乌江。降雨侵蚀力变化对长江上游输沙量变化贡献率为7%,对岷江、嘉陵江、乌江子流域输沙量变化的贡献率分别为36%、20%、9%。总体来说,降雨对长江上游输沙量变化的影响不如人类活动的影响大。

EFFECT OF THE BASIN RAINFALL EROSIVITY CHANGE ON THE RIVERINE SEDIMENT LOAD IN THE UPPER YANGTZE

Rainfall erosivity is one of the most important factors influencing riverine sediment load. However, riverine sediment load in response to rainfall erosivity change is not well understood in the upper Yangtze Basin. Based on the annual sediment load and daily rainfall data from 1956 to 2010 in the upper Yangtze Basin, we presented a quantitative estimate of changes in riverine sediment load in response to basin rainfall erosivity in the study area. The turning point of each subbasin was determined using double-mass curve and the critical years for subbasins of Jinsha, Min, Jialing, Wu and the upper Yangtze are 1999, 1993, 1985, 1984, and 1991 respectively. The effects of the basin rainfall erosivity change on the riverine sediment load were studied using linear regression analysis, and the contribution rates were estimated subbasin by subbasin. The result indicated that annual rainfall erosivity was relatively lower in the upper Yangtze Basin, with a value of 3 006 MJ·mm/(hm²·h·a), and there were great differences between the subbasins, the maximum of 5 055 MJ·mm/(hm²·h·a) appeared in the Wu subbasin, and the minimum of 1 560 MJ·mm/(hm²·h·a) in the Jinsha subbasin was less than one third of that in the Wu subbasin. The extremes ratios were sequenced as Jialing subbasin, Min subbasin, Wu subbasin, Jinsha subbasin. The annual sediment load was trending downward from 1956 to 2010 both in the upper Yangtze Basin and the subbasins, especially in the upper Yangtze Basin and Jialing subbasin where proved to has decreased dramatically. The upper Yangtze basin had an annual sediment load of 428 million tons, while subbasins of Jinsha, Min, Jialing and Wu varied in annual sediment load of 239 million t, 45 million t, 104 million t and 24 million t respectively. The contribution rate of rainfall erosivity on the sediment load variation in the upper Yangtze basin was 7%, and 36%, 20%, 9% for Min, Jialing, and Wu subbasins, respectively. But the increased rainfall erosivity of Jinsha subbasin did not decrease sediment load, therefore, it can be concluded that the decrease of sediment load of Jinsha subbasin was not mainly caused by rainfall. Generally speaking, rainfall has less influence on the sediment load change in the upper Yangtze than that of human activities.