Abstract
Abstract. The general relationships between vegetation and water yield under different climatic regimes are well established at a small watershed scale in the past century. However, applications of these basic theories to evaluate the regional effects of land cover change on water resources remain challenging due to the complex interactions of vegetation and climatic variability and hydrologic processes at the large scale. The objective of this study was to explore ways to examine the spatial and temporal effects of a large ecological restoration project on water yield across the Loess Plateau region in northern China. We estimated annual water yield as the difference between precipitation input and modelled actual evapotranspiration (ET) output. We constructed a monthly ET model using published ET data derived from eddy flux measurements and watershed streamflow data. We validated the ET models at a watershed and regional levels. The model was then applied to examine regional water yield under land cover change and climatic variability during the implementation of the Grain-for-Green (GFG) project during 1999–2007. We found that water yield in 38% of the Loess Plateau area might have decreased (1–48 mm per year) as a result of land cover change alone. However, combined with climatic variability, 37% of the study area might have seen a decrease in water yield with a range of 1–54 mm per year, and 35% of the study area might have seen an increase with a range of 1–10 mm per year. Across the study region, climate variability masked or strengthened the water yield response to vegetation restoration. The absolute annual water yield change due to vegetation restoration varied with precipitation regimes with the highest in wet years, but the relative water yield changes were most pronounced in dry years. We concluded that the effects of land cover change associated with ecological restoration varied greatly over time and space and were strongly influenced by climatic variability in the arid region. The current regional vegetation restoration projects have variable effects on local water resources across the region. Land management planning must consider the influences of spatial climate variability and long-term climate change on water yield to be more effective for achieving environmental sustainability.
Highlights
China’s Loess Plateau region stretches a total area of 0.64 million km2, and drains the upper and middle reaches of the mighty Yellow River (Fig. 1)
The streamflow of Loess Plateau region is dominated by surface runoff, and annual changes of soil water and groundwater are not likely to be large in order to cause a concern for annual estimate of ET by the water balance method
When pooling all the data of 134 point-scale measurements from the ten ET flux sites, we found that 61 %, 3.5 % and 17 % of monthly ET variability was explained by the terms potential ET (PET) · PPT, PPT · LAI and PET · LAI, respectively
Summary
China’s Loess Plateau region stretches a total area of 0.64 million km, and drains the upper and middle reaches of the mighty Yellow River (Fig. 1). Situated in a semi-arid to subhumid climate, the rugged Loess Plateau region has the world largest loess-paleosol deposit with a soil depth of up to 100 m on an elevation ranging from 1200 to 1600 m a.s.l. Due to the long history of human settlement, natural vegetation cover is generally low, and land uses are predominantly cultivated croplands. The Loess Plateau is one of the most severely eroded areas in the world due to the loose loess soils, steep slopes, high rainfall intensity, and poor vegetation conditions (Li et al, 2009). The soil erosion and sedimentation issues have long been recognised as a security threat to the livelihoods of local communities in the Yellow River Basin.
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