布哈河流域不同时间尺度下土壤侵蚀对气候变化的响应特征

Response of soil erosion to climate change in different time scales in Buha River

全球气候变暖极大地影响了地表侵蚀过程,但影响机制尚无统一定论。河流悬浮物是示踪地表侵蚀的常用手段。本文通过分析青海湖流域最大河流布哈河2008—2015年的日径流量、悬浮物浓度、气温及降雨数据,讨论了该流域在日、月以及季节尺度下土壤侵蚀对气候变化的响应特征。结果表明:降雨是半干旱布哈河流域土壤侵蚀的主要控制因素,气温通过影响冻融作用控制侵蚀行为。此外,该流域的土壤侵蚀具有明显的季节性差异,大部分的侵蚀发生在雨季。最重要的是,冻融作用导致春季解冻期/雨季前期产生额外的沉积物累积,表现为在相同流量下,沉积物输出明显高于雨季后期。上述结果对深刻认识全球变暖背景下侵蚀的响应机制具有重要的作用。

Background,aim,and scope Global warming greatly affects the process of surface erosion.Some suggest that global warming plays a catalytic role,but there is no consensus on the mechanism.The Buha River,the largest river in Lake Qinghai catchment,is prone to rapid response to climate change.Hydrometeorological data provide an insight to understand the impact of climate on erosion behavior and provide a basis for understanding the mechanism of soil erosion affected by global warming.Materials and methods The daily water discharge,suspended sediment concentration(SSC),air temperature,and precipitation were monitored by the Buha hydrological station during the period of 2008-2015.Suspended sediment flux(SSF)is the product of SSC and water discharge,which can be converted to different time scales.Results The water discharge and SSF show remarkable differences between the study period,and the daily/monthly values vary in several orders of magnitude.In addition,the erosion behavior of the basin displays obvious seasonal difference,i.e.most sediments are transported during the monsoon season.Besides,monthly SSC and discharge show clockwise loops from 2008 to 2015.Discussion The high erosion flux in the monsoon season is attributed to large runoff and flood events due to concentrated rainfall.Most importantly,freezing-thawing process results in additional sediment accumulation during the spring thawing period/pre-monsoon season,with sediment output significantly higher than post-monsoon season at the same water discharge.Conclusions The results demonstrate that rainfall is the main controlling factor of soil erosion in the semi-arid Buha River basin,and temperature controls erosion behavior by influencing freeze-thaw processes during spring thaw/pre-monsoon season.Recommendations and perspectives Multi-year daily hydrometeorological data are used for the first time to analyze the erosion behavior of the Buha River basin in different time scales,and the response of the process to climate is further discussed.These results are necessary for understanding the response mechanism of erosion in the context of global warming.