1901—2016年黄土高原土壤侵蚀格局演变及其驱动机制

Spatial-Temporal Development and Driving Mechanisms of Erosion on the Chinese Loess Plateau Between 1901 and 2016

黄土高原是我国乃至全球水土流失危害最为严重的地区之一。水土保持作为新兴学科,历史观测数据不足制约了对历史时期土壤侵蚀时空动态变化及其驱动机制认识的深化。为解决黄土高原土壤侵蚀模数历史数据缺乏问题,并为黄土高原土壤侵蚀演变过程研究及水土保持生态建设规划实施等提供方法与数据支撑,基于修正通用土壤流失方程RUSLE,首次建立了1901—2016年黄土高原土壤侵蚀模数逐年序列1 km分辨率栅格数据集,采用人类活动影响较小时期的22个黄河支流水文站实测输沙量验证了RUSLE对黄土高原土壤侵蚀模数模拟计算的结果具有较高精度。基于该数据集评估1901—2016年黄土高原土壤侵蚀模数时空变化特征,探讨了不同时期黄土高原土壤侵蚀模数变化的驱动机制。结果表明:黄土高原土壤侵蚀模数在1924年左右和1981年左右发生了2次突变,20世纪30—70年代土壤侵蚀面积和侵蚀模数持续上升,20世纪80年代—21世纪初土壤侵蚀模数持续降低,至21世纪初降为百余年来的最低值,2010—2016年平均土壤侵蚀模数受极端降雨影响出现小幅反弹;人类活动是黄土高原土壤侵蚀模数变化的主要驱动因素,而退耕还林(草)等正确的水土保持政策是控制黄土高原土壤侵蚀的根本驱动因素,人口增长导致森林过度砍伐、耕地扩张及过度放牧是20世纪30—70年代土壤侵蚀加剧的主要原因,20世纪80年代以后水土保持工程增加、植被覆盖度提高及农村能源结构变化是土壤侵蚀模数降低的重要原因;丘陵沟壑区和高塬沟壑区依然是黄土高原水土流失严重区域和治理的重点区域;鉴于全球气候变化背景下未来极端暴雨事件或将更加频繁,亟须创新黄土高原土壤侵蚀防治策略,重视沟谷坡侵蚀治理,强监管、重维护、提标准,提高防御极端暴雨造成严重水土流失灾害的能力。

The Chinese Loess Plateau has been suffering from soil erosion that is mostly severe across the world.Since soil and water conservation is an emerging discipline,a serious shortage of historic measurements largely constrained an in-depth understanding on the spatial-temporal pattern and driving mechanisms of erosion in the region.In order to address the shortage of historic erosion rates and to provide data and method support to erosion process study and the implementation of and soil and water conservation,Loess Plateau erosion rates between 1901 and 2016 were,for the first time,assessed by the Revised Universal Soil Loss Equation(RUSLE)at a 1 km spatial resolution in the study.The measured sediment yield in 22 tributaries of the Yellow River with little human interventions was used to validate the RUSLE results.The modeling results were found to be satisfactory,demonstrating RUSLE was capable of modeling erosion across the Loess Plateau.Based on the modeled erosion rates,spatial patterns of erosion rates over a century scale were studied,while the driving mechanisms of erosion rates for different periods were also investigated.The results demonstrate that two breaking points are found in the average erosion rates of the Loess Plateau during 1901-2016,which are around 1924 and 1981.Average erosion rate and eroded area of the Loess Plateau are dramatically increased from the 1930s to the 1970s,and the average erosion rate is decreased from the 1980s to the first decade of the 21st century,reaching the historic low during the 2000s.Finally,the average erosion rate is slightly rebounded during 2010-2016.Human activities and climate condition(particularly precipitation)are primary erosion driving factors,while the policy is a fundamental driving factor.Extensive deforestation and farming,driven by population increase,are the primary reason for the erosion increase between the 1930s and 1970s,while soil conservation engineering and re-vegetation lead to the erosion reduction since the 1980s.Hilly-gully region and gullied region are found to be mostly eroded areas on the Loess Plateau and thus the key regions for soil erosion control.Given that extreme rainfall events are likely to become more and more frequent under the global climate change,the innovative soil and water conservation strategy is urgently needed to achieve a strengthened supervision,more effective maintenance,higher standards,and improved capacity of controlling soil loss during extreme rainfall events.