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Wang H.,Chang'an University | Yang Z.,UNSCO IHE Institute of Water Education
Catena | Year: 2012

The hydro-climatic trends were examined for the lower reach of the Shiyang River Basin in NW China using the wavelet analysis and the Mann-Kendall (M-K) test. In order to identify the optimal combination of the hydro-climatic data series in the discrete wavelet transform (DWT), the results from DWT were tested by the Mann-Kendall test. The results showed that the discharge significantly decreased during the last five decades, while there was no noticeable change in precipitation. Temperature increased significantly in all periods, and evaporation decreased slightly in spring, summer and autumn. The results indicated that the DWT combination of DW1. +. DW2. +. DW4. +. DW5 was close to the real Mann-Kendall trend values. A 26-year periodicity in discharge was identified by applying the global wavelet spectra and continuous wavelet transform (CWT) method. Because the Shiyang River Basin is located in the cold region of NW China, the contribution of glacier and snow to the discharge is significant. Therefore, the significantly increased temperature during the last 50. years would eventually lead to an increased discharge due to the increased amount of melt water from glacier and snow. However, the increasing water demand for the economic development and oasis expansion in the middle reach of the basin will reduce discharge flowing into the lower reach of the basin. Compared to the impact of climate change, it should be pointed out that the flow regime is strongly affected by human activities. © 2012 Elsevier B.V.

Yin L.,UNSCO IHE Institute of Water Education | Yin L.,Key Laboratory of Groundwater and Ecology in Arid and Semiarid Zones of China Geological Survey | Zhou Y.,UNSCO IHE Institute of Water Education | Huang J.,Key Laboratory of Groundwater and Ecology in Arid and Semiarid Zones of China Geological Survey | And 8 more authors.
Environmental Earth Sciences | Year: 2014

Sap flow (SF)of a willow tree, meteorological variables, soil water content, and water table depth were measured during the growing period from mid-April to October, 2011 in the semi-arid Hailiutu River catchment, Northwest China. The measurements of SF showed diurnal fluctuations in sunny days and seasonal changes from 1.65 l/h in mid-April to 33 l/h in July. At hourly scale, SF is significantly correlated with net radiation, followed by air temperature, relative humidity, and wind speed. At daily scale, air temperature affects the dynamics of SF significantly. Daily SF correlates positively with net radiation and negatively with relative humidity. There is no correlation observed between daily SF and wind speed. The measurements of SF do not indicate water stress although the experimental period is dry. Correlation analysis shows that SF is strongly correlated with soil moisture and water table depth, indicating the willow tree uses both soil water and groundwater for transpiration. © 2013 Springer-Verlag Berlin Heidelberg.

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