黄土高原现状产沙情势评价

在黄河来沙锐减背景下，厘清现状黄土高原在不同降雨情景的年均产沙量，对客观认识黄河未来水沙情势具有十分重要的意义。本文分析了过去60年黄土高原汛期径流及含沙量变化特点，认为该区2010年以来的下垫面可作为现状产沙情势评价的代表下垫面。采用理论推算和实际产沙能力分析等两种方法，计算了黄土高原现状下垫面在4种降雨情景下的年均产沙量。结果表明，如果汛期降雨较1956—2019年均值偏丰0～17.3%,2010—2019年下垫面的年均产沙量为3.9亿t/a～5亿t/a;若基于2018年以来的下垫面，其年均产沙量为3.6亿t/a～4.5亿t/a;受坝库工程拦截影响，可输送至潼关断面的沙量更少。分析了黄土高原植被和梯田的发展趋势，并考虑流域产沙指数与植被梯田覆盖状况的响应规律，认为该区产沙能力进一步降低的潜力很小。事实上，由于年降雨量450 mm以下地区的新生植被抵御恶劣气候和人类干扰的能力较低，黄土高原产沙量存在反弹至5亿t/a～8亿t/a的风险。

Evaluation on present status of sediment yield in the Loess Plateau

In the context of rapid decreasing sediment yield in the Yellow River, it is of great significance to clarify the average annual sediment yield of the Loess Plateau under different rainfall scenarios for the objective evaluation of the future sediment situation of the Yellow River. The characteristics of the runoff and sediment concentration changing in the past 60 years were analyzed, which indicates that the area''s underlying surface since 2010 is suitable to be used for evaluating the present situation of sediment yielding capacity in the Loess Plateau. Two methods, the theoretical calculation and the actual capacity analysis of sediment production, were used to analyze the average annual sediment yields (AASY) of the Loess Plateau under four different rainfall scenarios, and the results show that AASY in 2010-2019 are between 0.39 and 0.5 billion t/a, if the rainfall in flood season is about 0~17.3% more than the average value in 1956-2019; the AASY are range from 0.36 to 0.45 billion t/a in 2018. Affected by the sediment trapping capacity of check dams and reservoirs in the area, the sediment load transported to Yellow River''s Tongguan section would be much less than the sediment yield in the Loess Plateau. Based on the analysis of vegetation-terraces development trend on the Loess Plateau and relationship between sediment yield and vegetation-terraces coverage degree, it is considered that sediment yielding capacity in the Loess Plateau has less potential to decrease further. In fact, there is risk that the sediment yields rebound back to 0.5~0.8 billion t/a, because of the poor ability of the new vegetation to resist bad climate interference in the area with average precipitation less than 450 mm.