Is the runoff coefficient increasing or decreasing after ecological restoration on China’s Loess Plateau?
2021
Zheng, Haiyan | Miao, Chiyuan | Zhang, Guanghui | Li, Xiaoyan | Wang, Shuai | Wu, Jingwen | Gou, Jiaojiao
The “Grain for Green” project (GGP) was launched in 1999 on China’s Loess Plateau to reduce soil erosion, which had far-reaching impacts on the local eco-hydrological processes. In this study, we use monthly runoff depth and precipitation datasets spanning 1961 to 2015 for 16 primary basins of the plateau to reveal changes in runoff generation capacity before and after the GGP. We use a Budyko-based elasticity method to calculate the runoff depth (R₁) and runoff coefficient (C₁) exclusively attributable to land use/cover change. Results indicate that the mean annual runoff coefficients (C₀) decline by 26%–76% from the periods 1961–1999 to 2000–2015. The annual observed runoff depth (R₀) and C₀ for 75% of basins show significant downward trends during 1961–1999; after the implementation of the GGP, both annual R₀ and annual C₀ for over 50% of basins show upward trends. The study further finds that the increase of erosive rainfall during the period 2000–2015, whose mean increasing rate reaches 4.6 mm/year, is the main reason for the upward trends of R₀ and C₀. After removing the effect of precipitation variation during this period, we find that 11 out of 16 basins show decreased trends for C₁, with the downward rate between 2.4% and 6.0% per year. The reduction rate in semi-arid areas is about four times the rate in semi-humid areas. The results remind us to consider the carrying capacity of local water resources when implementing soil and water conservation measures across the Loess Plateau.
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