Handan Zhang

Effect of rainfall variation and landscape change on runoff and sediment yield from a loess hilly catchment in China

The semiarid Chinese Loess Plateau is notorious for severe drought, water erosion, and environmental degradation. Changes in landscape patterns and rainfall are key drivers that determine the dynamics of runoff loss and sediment yield from catchments. These factors have crucial implications for management of other fragile ecosystems around the globe. In this study, responses of surface runoff and sediment yield to land use and rainfall in a typical loess hilly catchment in 1997, 2005, and 2010 were analyzed. Several major findings are highlighted. First, most rainfall occurred in the growing season from June to September and increased only slightly during the observation years. Second, runoff and soil transport rates at the catchment outlet from June to August were far greater than in other months. A similar trend was observed for seasonal rainfall occurrence, indicating that the intra-annual water erosion patterns were largely dominated by monthly rainfall distribution. Third, compared with the time period 1997–2005, mean runoff and sediment transport modulus in 2005–2010 declined significantly. This can be attributed mainly to changes in land use/land cover, i.e., increases in forests, shrubs, and grasses, and decreases in sloping farmlands. Dam construction is also key in controlling runoff and sediment yield, but more attention must be paid to its possible negative environmental effects. In general, our study indicates that marked changes in landscape patterns and vegetation coverage may contribute to long-term soil loss dynamics, and intra-annual rainfall variation mainly contributes to monthly variation in runoff and sediment yield.

Evaluating canopy transpiration and water use of two typical planted tree species in the dryland Loess Plateau of China

State Key Laboratory of Urban and Regional Ecology, Research Center for Eco‐Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China University of Chinese Academy of Sciences, Beijing 100049, China Correspondence Wei Wei, State Key Laboratory of Urban and Regional Ecology, Research Center for Eco‐Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China. Email: weiwei@rcees.ac.cn Funding information National Natural Science Foundation of China, Grant/Award Number: 41371123, 41390462 and 41401209, National Key Research and Development Program of China, Grant/Award Number: 2016YFC0501701, and the National Advanced Project of the Twelfth Five-year Plan of China, Grant/Award Number: 2015BAC01B02

Identification on threshold and efficiency of rainfall replenishment to soil water in semi-arid loess hilly areas

As one critical source of water for maintaining ecosystems in arid and semi-arid regions, rainfall replenishment to soil water can determine vegetation growth and ecosystem functions. However, the limited rainfall resources were often not used effectively in the semi-arid loess hilly areas due to random temporal and spatial distribution of rainfall and specific vegetation features. Thus, it is highly significant to determine the threshold and efficiency of rainfall replenishment to soil water under different vegetation types. The threshold and efficiency can offer scientific evidence for rehabilitating vegetation and improving efficiency of using rainfall resources. In this study, the efficiency and threshold of rainfall replenishment to soil water were determined under natural grassland, wheat, artificial grassland, sea buckthorn shrubland and Chinese pine forestland based on consecutive measurements. The results indicated that the lag-time, rate, efficiency of rainfall replenishment to soil water were closely related to vegetation type, with significant differences existing among different vegetation types. The lag-time for natural grassland in the soil horizon of 20 cm was the shortest one (26.4 h), followed by wheat (27.8 h), sea buckthorn (41.8 h), artificial grassland (50.0 h) and Chinese pine (81.8 h).The value of replenishment rate, followed the order of wheat (0.40 mm h–1)> natural grassland (0.30 mm h–1)> sea buckthorn (0.17 mm h–1)> artificial grassland (0.14 mm h–1)> Chinese pine (0.09 mm h–1). As for the efficiency of rainfall replenishment to soil water, natural grassland was the most efficient one (35.1%), followed by wheat (29.2%), sea buckthorn (16.8%), artificial grassland (11.5%), Chinese pine (4.2%). At last, it was found that wheat had the lowest threshold (6.8 mm) of rainfall replenishment to soil water, which was followed by natural grassland (10.5 mm), sea buckthorn (20.5 mm), artificial grassland (22.6 mm) and Chinese pine (26.4 mm). These results implied that soil water in natural grassland was sensitive to rainfall and easily to be replenished, while soil water in Chinese pine was harder to be replenished by rainfall compared to other vegetation types.