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Liu Z.,University of Heidelberg | Zhou P.,Guangdong Academy of Forestry | Zhang F.,Guangdong Academy of Forestry | Liu X.,Academy of Water Resources Conservation Forests in Qilian Mountain of Gansu Province | Chen G.,Chinese Academy of Forestry
Agricultural and Forest Meteorology | Year: 2013

It is vital to understand long-term drought variability and its causes for better water resource management in precipitation deficit regions. In order to assess the characteristics and potential risk of drought in Qinghai Province (as a typical arid and semi-arid area in China), the temporal trends of precipitation and temperature data (daily records from 1961 to 2006) of 44 stations across this province were firstly detected using the Mann-Kendall trend test. The self-calibrating Palmer drought severity index (PDSI), rotated empirical orthogonal function (REOF), and continuous wavelet transform (CWT) were used to further evaluate and investigate spatial patterns, temporal variations and periodicities of dryness/wetness conditions in Qinghai. The results show that: (1) A significant increasing trend in annual mean temperature can be detected in most parts of Qinghai over the last five decades, especially in Qaidam Basin. A non-significant downward trend in annual precipitation can be found in the eastern and southeastern regions of the province; (2) Four dominantly geographical sub-climate regions of dryness/wetness conditions were identified - the source region (Tuotuo River) of the Yangtze River, Qaidam Basin, the Qilian Mountains area, and the eastern agricultural area; (3) With respect to temporal variations of dryness/wetness conditions in each sub-region, only the source region (Tuotuo River) of the Yangtze River indicates a long-term wet tendency over the past 46 years; (4) A 3-5-year significant (at 95% confidence level) periodical oscillation can be detected in the PDSI series of the source region of the Yangtze River and 5-7-year and 8-10-year periods exist in Qaidam Basin. However, periodical features in the Qilian Mountains and eastern agricultural area are not statistically noticeable. The results of this study will be beneficial for water resource management, forecasting, and preparations for potential drought hazards in Qinghai Province and also be a valuable reference for other arid and semi-arid areas. © 2013 Elsevier B.V. Source

Yu P.,Chinese Academy of Forestry | Wang Y.,Chinese Academy of Forestry | Wu X.,Inner Mongolia University | Dong X.,Chinese Academy of Forestry | And 6 more authors.
International Journal of Sediment Research | Year: 2010

Forestation has been encouraged worldwide due to increasing demand for forest products, and for its ecological benefits such as soil erosion control and sediment reduction. However, forestation reduces runoff, thus potentially aggravating water shortages in arid regions. In order to quantitatively estimate the possible water yield reductions caused by forestation in an arid region, a small watershed (the Pailugou watershed) in the Qilian Mountains of northwest China was chosen as a study area. The responses of hydrological dynamics to different forestation scenarios in the study area were simulated using the TOPOG model. The results showed that forestation could lead to a complete loss of runoff at the site scale. At the watershed scale, a 10% increase in forest coverage led to a runoff reduction of 25.6 mm, equivalent to 13% of the runoff in the un-forested watershed. However, due to climatological and topographical constraints, the potential forest distribution occupied only 46.3% of the watershed area, and runoff reduction was estimated to reach a maximum of 60% when the forest cover ratio increased from 0.41% to 46.1%. Actual forest coverage is 36% in the study area, thus the water yield will be reduced with any further increase in forest area. Our study suggested that a trade-off between the numerous benefits of forest coverage increase and its negative impact on water yield should be carefully addressed in arid regions with inherently severe water-shortage. © 2010 International Research and Training Centre on Erosion and Sedimentation and the World Association for Sedimentation and Erosion Research. Source

Zhang L.,Chinese Academy of Forestry | Yu P.-T.,Chinese Academy of Forestry | Wang Y.-H.,Chinese Academy of Forestry | Wang S.-L.,Academy of Water Resources Conservation Forests in Qilian Mountain of Gansu Province | And 3 more authors.
Forest Research | Year: 2015

The structures of Qinghai spruce (Picea crassifolia) forests in Dayekou watershed on the northern slope of Qilian Mountains were studied along the altitude from 2 500~3 300 m, and the values were calculated with sub-segment elevation (per 100 m a. s. l.). The results are as follows. (1) The forest density was high while the trees were relatively small in the study area. The forest density, DBH, H and crown diameter of stands were 1 550 ± 628 trees·hm-2, 13.9 ± 6.2 cm, 8.1 ± 3.7 m and 3.3 ± 1.7 m, respectively. With the elevation increasing, the forest density, the average DBH and the crown diameter decreased. The average H showed a "unimodal" change. (2) The saplings (DBH 5~12.5cm) and middle trees (DBH 12.5~22.5cm) were predominant in the forests, and the height of trees were about 6~12 m. With the elevation increasing, the percentage of seedlings (DBH≤5 cm) in forest showed a basic stability, the percentage of saplings decreased slightly, the percentage of middle trees showed a "unimodal" change, which peaked at 2 800~2 900 m a. s. l., the percentage of big trees (DBH>22.5 cm) increased. The percentage of the stands (H≤6 m) showed a "V" shaped change, which the minimum value appeared at 2 800~2 900 m a. s. l.. The percentages of the stands (H: 6~12 m) and the stands (H >12 m) showed "unimodal" changes, peaking at 2 600~2 700 m and 2 800~2 900 m a. s. l., respectively. (3) The ratio of height to diameter ranged from 0.45~0.73 and the breast-height basal area ranged from 7.86~33.32 m2· hm-2, with the elevation increasing, both of them showed a "unimodal" change, which peaked at 2 800~2 900 m a. s. l.. Analysis shows that the stand density, moisture and temperature conditions were leading to the differentiation of the growth in tree diameter and height. The middle segment elevation (2 800~2 900 m a. s. l.) is the most suitable area for Qinghai spruce forests distribution in this area. ©, 2015, Chinese Academy of Forestry. All right reserved. Source

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