Hydro-climatic trends in the last 50years in the lower reach of the Shiyang River Basin, NW China

Abstract 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.