An event-based approach to understanding the hydrological impacts of different land uses in semi-arid catchments Shengping Wang a , Zhiqiang Zhang b,d,⇑ , Tim R. McVicar c , Jianjun Zhang d,b , Jinzhao Zhu d,b , Junting Guo b,d a Sino-Canada Research Academy of Energy and Environmental Studies, North China Electric Power University, Beijing 102206, PR China b Key Laboratory Soil and Water Conservation and Desertification Combating, Ministry of Education, College of Soil and Water Conservation, Beijing Forestry University, Beijing 100083, PR China c CSIRO Land and Water, GPO Box 1666, Canberra ACT 2601, Australia d Jixian Forest Ecosystem Observation and Research Station, Chinese National Ecosystem Observation and Research Network, College of Soil and Water Conservation, Beijing Forestry University, Beijing 100083, PR China article info Article history: Received 26 January 2011 Received in revised form 6 October 2011 Accepted 16 November 2011 Available online 25 November 2011 This manuscript was handled by Philippe Baveye, Editor-in-Chief, with the assistance of Xunhong Chen, Associate Editor Keywords: Land use change Event hydrological impacts Re-vegetation Semi-arid region Loess Plateau summary In semi-arid catchments around the world re-vegetation is often implemented to reduce quick surface runoff, combat severe soil erosion, restore degraded ecosystem functionality, and, ultimately, improve ecosystem productivity. However, to date, in these water stressed regions, the event-based hydrological impact of different land uses induced by re-vegetation activities is not fully understood at the watershed scale. Traditional hillslope plot experiments and paired watershed experiments have proved difficult to up-scale to a watershed level. In 2006 and 2007, we used broad-crested weirs to measure event stream- flow from six catchments within the Caijiachuan watershed (area = 40.1 km 2 ), located in the Loess Pla- teau, a semi-arid region in China. The six catchments have different land use compositions with functional combinations of crop, grassland, shrubland, secondary forest, and plantations. Over the same period, event rainfall was measured by a network of rainfall gauges deployed over the study site. We examined the difference in hydrological properties between the catchments using the non-parametric Firedman test, and differentiated the role of each land use in governing watershed hydrology using a numerical analysis technique. Our results showed important differences between the six catchments with respect to event runoff coefficients, normalized peak flow, and event duration. Each land use played a different role in catchment hydrology, as shown by the different mean runoff coefficients (rc) and mean representative surface flow velocities (V). Compared to secondary forest (rc = 0.017 and V = 0.07 m s 1 ), plantations (rc = 0.001 and V = 0.18 m s 1 ) provide a greater potential for increasing shearing force and had a larger impact on runoff reduction. Although shrubland (rc = 0.096 and V = 0.20 m s 1 ) and grassland (rc = 0.127 and V = 0.02 m s 1 ) have similar magnitude of mean runoff coefficients, grassland seems more capable of trapping sediment due to its lower surface runoff velocity. Cropland (rc = 0.008 and V = 0.05 m s 1 ) exerted an important effect on runoff reduction and a moderate effect on flow retardation. We concluded that, to combat severe soil erosion while minimizing water use, re-vegetation in the semi- arid Loess Plateau should not overly, or even solely, rely on plantations. Alternatively, to produce the desired ecosystem functionality, preservation and establishment of grassland during re-vegetation pro- cesses should be encouraged, at least, in the early stage of ecological restoration within a ‘‘successional re-vegetation’’ framework. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction Soil erosion is a serious problem in semi-arid catchments (Irvem et al., 2007; Dunjo et al., 2004), resulting in on-site produc- tivity losses, ecological degradation, a poverty trap for local inhab- itants, and severe downstream environmental problems (Fu and Gulinck, 1994; Kang et al., 2001; Hessel et al., 2003; McVicar et al., 2007a). In addition to key soil and rainfall properties (espe- cially rainfall intensity), vegetation cover and land management are particularly important for controlling runoff generation in semi-arid catchments by directly determining the hydraulic rough- ness of the surfaces where overland flow occurs (Bryan and Campbell, 1986; Kosmass et al., 1997; Mitchell, 1990; Candela et al., 2005). To effectively control severe soil erosion, re-vegeta- 0022-1694/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jhydrol.2011.11.035 ⇑ Corresponding author. Address: Key Laboratory of Soil and Water Conservation and Desertification Combating, Ministry of Education, College of Soil and Water Conservation, Beijing Forestry University, Qinghua East Road 35#, Haidian District, Beijing 100083, PR China. Tel.: +86 10 62338097; fax: +86 10 62337873. E-mail address: Zhqzhang@bjfu.edu.cn (Z. Zhang). Journal of Hydrology 416–417 (2012) 50–59 Contents lists available at SciVerse ScienceDirect Journal of Hydrology journal homepage: www.elsevier.com/locate/jhydrol