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ABSTRACT The arid region in northwestern China covers 2·02 million square kilometres and is one of the most arid regions in the world. Positioned at the central part of the Eurasian Continent, this region experiences little influence from the Eastern and Southern Asian Monsoons and precipitation is formed mostly from westerly vapour. With a hyper arid climate, the annual precipitation in this region ranges from less than 20 mm at the oasis area to around 600 mm in the mountain regions, whereas potential evaporation can amount to 2000-3000 mm per annum. It is reported that strong evapotranspiration characterizes and dominates the water cycle in the arid basins. Nearly all the water resources of the oasis, where the human society exists, come from the mountain areas as river discharge from glacier/snow melting water, rainfall and subsurface flow from bedrock cracks. As a result, the hydrographs of the arid basins are affected by climate change via changes in precipitation partitioning (the ratio of rainfall and snowfall) and changes to seasonal distributions of precipitation and air temperature. These changes in turn directly affect the water yield and the vegetation response. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Natural forests in southern China have been severely logged due to high human demand for timber, food, and fuels during the past century, but are recovering in the past decade. The objective of this study was to investigate how vegetation cover changes in composition and structure affected the water budgets of a 9.6-km2 Dakeng watershed located in a humid subtropical mountainous region in southern China. We analyzed 27 years (i.e., 1967-1993) of streamflow and climate data and associated vegetation cover change in the watershed. Land use/land cover census and Normalized Difference of Vegetation Index (NDVI) data derived from remote sensing were used to construct historic land cover change patterns. We found that over the period of record, annual streamflow ( Q) and runoff/precipitation ratio did not change significantly, nor did the climatic variables, including air temperature, Hamon’s potential evapotranspiration (ET), pan evaporation, sunshine hours, and radiation. However, annual ET estimated as the differences between P and Q showed a statistically significant increasing trend. Overall, the NDVI of the watershed had a significant increasing trend in the peak spring growing season. This study concluded that watershed ecosystem ET increased as the vegetation cover shifted from low stock forests to shrub and grasslands that had higher ET rates. A conceptual model was developed for the study watershed to describe the vegetation cover-streamflow relationships during a 50-year time frame. This paper highlighted the importance of eco-physiologically based studies in understanding transitory, nonstationary effects of deforestation or forestation on watershed water balances. [ABSTRACT FROM AUTHOR]

Information on evapotranspiration (ET) can help us understand water balance, particularly in forested watersheds. Previous studies in China show that ET was relatively low (30-40% of total precipitation) in the Minjiang Valley located in the upper reach of the Yangtze River Basin. However, this conclusion was derived from research on small-scale watersheds (<100 km2). The objective of this paper was to present ET information on meso-scale watersheds in the Minjiang Valley. Four meso-scale watersheds (1,700-5,600 km2) located in the Minjiang Valley were used to estimate ET using the water balance approach. We first generated forest vegetation variables (coniferous forest percentage, forest cover percentage, and derived forest vegetation index) using remote sensing data. Landsat 5 TM satellite images, acquired on June 26, 1994, were selected for the vegetation classification. Actual annual ET was calculated based on 11-year estimated precipitation and measured streamflow data (1992-2002). We also calculated potential ET (PET) using an improved Thornthwaite model for all four watersheds for the period of 1992-1998. PET can provide additional information about potential capacity of water flux to atmosphere in the region. Seasonal (dry and rainy) PET and ET for all studied watersheds were also estimated for comparison purposes as the water balance approach, at shorter than annual scales, would likely provide inaccurate estimates of ET. The dominant vegetations in the Minjiang Valley were grasslands, conifer forests, and shrub-lands. Our results confirmed that both ET and PET for three studied meso-scale watersheds in the Minjiang Valley is relatively low (39.5-43.8 and 28.2-47.7% for ET and PET, respectively), with an exception of ET in the Yuzixi watershed being 71.1%. This result is generally consistent with previous research at small watershed scales. Furthermore, the low ET across various scales in the Minjiang Valley may be related to the unique deeply cut valley environment. [ABSTRACT FROM AUTHOR]

The long-term hydrological response to reforestation is critical to regional water management, especially in areas where large-scale reforestation has been practiced. In this study, we investigated the long-term hydrological response to reforestation in the 579 km2 basin in southeastern China through ground-based monitoring of water yield, sedimentation, vegetation cover and climate in the basin. The vegetation dynamics were also examined by remote sensing data (MSS, Landsat and AVHRR NDVI). We found that forest cover increased 23% or 13 593 ha from 1975 to 2002. Meanwhile, annual water yield decreased 86-88 mm from 1971-1983 (i.e. pre-reforestation) to 1984-2009 (i.e. post-reforestation). These decreases were significant statistically according to both regression and double mass analyses. Time series analysis demonstrated that there was a clear decline in annual sediment yield and an increase in annual evapotranspiration (ET) over the period from 1971 to 2009. We concluded that reforestation could significantly reduce annual water yield and sediment yield in the basin because of the forest cover change and forest growth. This conclusion is consistent with findings from widely paired-watershed studies and literatures published on the impact of reforestation in large watersheds. Our results also have important strategic implications and provide insight into more sustainable forest management practices for the future. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The Budyko formula for estimating the long-term average annual evaporation is applied to calculate the long-term water balance in 29 humid watersheds of southern China. As a result of overestimation of evaporation, the long-term average annual runoff is underestimated, with the Nash-Sutcliffe efficiency (NSE) at just − 17%. A one-variable linear regression model is employed to find that the Budyko scatter and the relative errors of Budyko runoff and evaporation estimates are all closely related to the long-term aridity index. Through combining the original Budyko formula with the different linear regression models for estimating the Budyko estimation errors, three forms of revised Budyko equation for estimating the long-term average annual runoff are derived, with all their NSE values to be around 66%. After calibration, both one-parameter Turc-Pike and one-parameter Fu equations lead to the NSE value of 60% in estimating long-term average annual runoff. Two conclusions are made, with the first one being that, the nonparametric Budyko formula, although very intuitive and very simple, does not apply well in calculating long-term water balance in 29 humid watersheds in southern China. The second one is that, the parametric evaporation formulae, with locally optimized parameter values, can achieve better accuracy in estimating long-term average annual evaporation and runoff than the nonparametric Budyko evaporation formula. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The effect of forests on annual water yield is an unresolved central issue in forest hydrology despite years of study. There has been a particular shortage of research in the mountains of arid inland river basins. In the present study, we examined the effects of forests on hydrology using data on precipitation, evaporation, canopy interception, transpiration, and runoff from 1994 to 2008 for the Pailugou catchment of northwestern China's Qilian Mountains. We modelled the water balance to assess the contribution of different vegetation types to annual water yield. In our study area, Picea crassifolia forest covered 38·5% of the catchment area, but contributed little to annual water yield. For an annual average precipitation of 407·1 mm (from 2003 to 2008) at an elevation of 2700 m, the runoff depth from the forest was 11·6 mm, accounting for only 3·5% of total annual water yield of the catchment. For an annual average precipitation of 374·1 mm (from 1994 to 2002), the runoff depth from the forest was − 14·3 mm (i.e. 5·9% of total annual water yield of the catchment was consumed to sustain tree growth). This has significant implications, because forests are increasingly being planted in the Qilian Mountains, and this may decrease the downstream water supply. Thus, the relationship between the forest and water yield must be better understood to permit the establishment of an appropriate regional level of forest cover. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The article offers information on the description of a hydrological model that considers the five categories of land use. It states that the verification and calibration model were executed at two independent watersheds which include Tangnaihai and Lushi in China. Moreover, the results suggest only a small change in evapotranspiration, yet a marked decreased in precipitation, which was important in all analysed areas excluding the Lanzhou-Toudaoguai inter-watershed area.