Streamflow and Sediment Declines in a Loess Hill and Gully Landform Basin Due to Climate Variability and Anthropogenic Activities

Abstract

Streamflow and sediment runoff are important indicators for the changes in hydrological processes. In the context of environmental changes, decreases in both streamflow and sediment (especially in the flood season) are often observed in most of the tributaries of the middle Yellow River in China’s Loess Plateau. Understanding the effect of human activities could be useful for the management of soil and water conservation (SWC) and new constructions. In this paper, changes in streamflow and sediment during the flood season (June–September) of the 1966–2017 period in a typical loess hill and gully landform basin were analyzed. Basin-wide rainfall of the flood season decreased nonsignificantly with an average rate of −0.6 mm/flood season for the whole study period by using the trend-free pre-whitening based Mann–Kendall trend test, while the decreasing rate was weakened on the time scale. A remarkable warming trend (1985–1999) and two decreasing trends (1966–1984 and 2000–2017) were observed, and the overall increasing trend could be found in air temperature series with a rate of 0.01 °C/flood season during the study period. Statistical models were developed to describe the rainfall-runoff and rainfall-sediment processes in the pre-impact period (when the hydrological series was stationary). Furthermore, the relative effects of climate variability and human activities on hydrological changes were quantified. Results proved the dominant role of human activities (versus climate variability) on the reductions of both streamflow and sediment load. The relative contribution of human activities to streamflow decrease was 84.6% during the post-impact period 1995–2017, while the contributions were 48.8% and 80.1% for two post-impact periods (1982–1996 and 1997–2017), respectively, to the reduction of sediment load. Besides, the effect of the exclusion of anomalous streamflow or sediment events on change-point detection was also analyzed. It indicated that the anomalous events affect the detection of change points and should be given full consideration in order to decide whether to remove them in the change-point detection. Otherwise, the full series with anomalous samples will completely affect the attribution results of hydrological changes. We also suggest that large-scale SWC measures with different construction quality and operational life could intercept and relieve most floods and high sediment concentration processes, but may amplify the peaks of streamflow and sediment when the interception capacities are exceeded under the condition of extreme rainstorm events.

Anthropocene Geomorphic Change. Climate or Human Activities?

“…However, numerous contributions have pointed out the sediment load reduction experienced by many rivers as a result of human activities (Chang et al, 2019;Dang et al, 2010;Dearing & Jones, 2003;Golosov & Walling, 2019;Gupta et al, 2012;Hu et al, 2009;Hu et al, 2019;Latrubesse et al, 2017;Li et al, 2016;Miao et al, 2011;Rahman et al, 2018;Shi et al, 2017;Vinh et al, 2014;Wang et al, 2011;Wang et al, 2015;Wu et al, 2018;Yang et al, 2002;Yang et al, 2015;Yu et al, 2013;Zhang et al, 2016;Zhou et al, 2016). Reservoir construction, and other modifications of river courses, considerably reduces connectivity between erosion areas in the basins and channel sectors downstream dams, the latter playing a main role (Kondolf, 1997;Graf, 1999Graf, , 2001Graf, , 2005Graf, , 2006Magilligan & Nislow, 2001, 2005Magilligan et al, 2003;Nilsson et al, 2005;Petts, 2009;Dai & Liu, 2013;Magilligan et al, 2013;Petts & Gurnell, 2013;Pal, 2016).…”

“…Walling and Fang (2003), studying sediment load in 145 large river basins for a period >25 years, found that about 70 showed no significant change, 68 showed reductions attributable to reservoir construction, and 7 experienced increases that could be explained by land use changes. Many other contributions (Wang et al, 2007(Wang et al, , 2011Zhang & Lu, 2009;Miao et al, 2011;Du & Shi, 2012;Gupta et al, 2012;Yang et al, 2015;Li et al, 2016;Liu et al, 2017;Wu et al, 2018;Hu et al, 2019;Chang et al, 2019) have attributed the reduction of sediment load mainly to human activities, among which dams appear to be the most important. In particular, Yang et al (2015) concluded that between 1950-1968 and 2003-2012 the reduction of sediment load observed in rivers could be explained by reservoirs (~88%), other human activities (~7%), and rainfall changes (~5%); and Syvitski et al 200510.1029/2019EF001305…”

Impacts of infiltration holes on rainfall‐runoff production on slopes treated with engineering measures: A simulation study in the Loess Plateau of China

“…Since the 1950s, some engineering and biological measures such as fish‐scale pits, level ditches, level benches, terraces, and afforestation have been implemented on the Loess Plateau of China (Chen et al, 2020; Zhao et al, 2017). Soil and water loss was further reduced with the implementation of the “Grain for Green” project from 1999 (Chang et al, 2019; Fu et al, 2017). The average annual sediment flux from 2000 to 2010 (0.32 ± 0.24 Gt year −1 ) across the Loess Plateau was less than one quarter of that from 1950 to 1980 (1.34 ± 0.24 Gt year −1 ) (Wang, Fu, et al, 2016).…”

Insights on the Impacts of Hydroclimatic Extremes and Anthropogenic Activities on Sediment Yield of a River Basin

“…Climate change and anthropogenic activities pose a substantial risk of river system alterations [1][2][3]. The changes in environmental processes have important implications on hydrologic and sediment cycles.…”