Rainfall event based runoff prediction model for small watersheds in the Loess Plateau
Wang Hao, Zhang Ganghui, Zhang Yongxuan, Geng Ren, Luan Lili
1. School of Geography,Beijing Normal University, 100875, Beijing, China;2. State Key Laboratory of Earth Surface Processes And Resource Ecology, Beijing Normal University,100875, Beijing, China
Abstract：Situated in northwestern China, the Loess Plateau is covered with loose, fine, uniform, and highly erodible aeolian deposits. The climate varies from semi-arid to sub-humid, with heavy short storms. Because of the erodible soils, steep slopes, heavy storms, low vegetation cover and inappropriate land use, it is one of the most eroded regions in the world. Such serious soil erosion has slowed down socio-economic and environmental development by its direct and indirect influence in this region. Many researchers have realized the seriousness of this issue and started the study of the ways to conserve soil and water, in order to achieve sustainable development of the socio-economic environment by controlling soil erosion and restoring the disturbed ecosystem. They found that rainfall event based runoff in small watersheds was one of the key ways to study soil erosion in the Loess Plateau. However, most of the researchers only focus on subzone Ⅰ. The precipitation and the watershed geometry were divergent at different subzones because of the difference of the climate, soil, shape, and land use. So, it is necessary for the other subzones to develop a rainfall event based runoff prediction model for small watersheds in the Loess Plateau. In this study, we collected precipitation and runoff date from 57 small watersheds and built a database which included 2 424 rainfall events distributed in the subzones Ⅰ, Ⅱ, Ⅲ, Ⅴand the Plateau subzone, in the Loess Plateau. We simulated the relationship between the runoff depth and the parameters which represent precipitation and watershed geometry, so as to sort out the dominant factors affecting runoff depth in the Loess Plateau. The model was developed based on 1700 (70%) rainfall events data, and the rest was used for validation. Results showed that the watershed area, the watershed shape, the rainfall amount and the average rainfall intensity were the dominant factors affecting runoff depth in the Loess Plateau. The non-linear regression models were developed based on the four factors for different subzones with the NSE greater than 0.542. The NSE of validation was greater than 0.410. The results showed that runoff depth is negatively correlated with the watershed area, but positively correlated with the shape of the watershed, the rainfall amount and the average rainfall intensity. The impacts of the precipitation and the watershed geometry on runoff depth were similar at different subzones, but the strength of the impacts varied at different subzones. The models are accurate for different subzones, have a simple structure, and the parameters were easy to obtain. So, they can be popularized to different regions in the Loess Plateau. Our results are helpful to the comprehensive management of small watershed planning in the Loess Plateau, especially for the design of soil and water conservation measures.
2015, Vol. 13 
