Since the 20 th century, numerous Quaternary moraine dating methods have emerged, including lichenometric, moraine 14 C, quartz sand thermoluminescence(TL), electron spin resonance(ESR), optically stimulated luminescence(OSL) and 10 Be, 26 Al, 36 Cl, 3H, 21 Ne nuclide dating methods. These dating methods are widely applied to determine moraine ages and have provided a large dataset. Unfortunately each method has its defects. In this paper, we will review these various dating methods and provide some comments.
In recent years, climate change has been aggravated in many regions of the world. The Hexi Corridor is located in the semiarid climate zone of Northwest China, which is particularly affected by climate change. Climate change has led to the spatial and temporal variations of temperature and precipitation, which may result in hydrological drought and water shortage. Thus, it is necessary to explore and assess the drought characteristics of river systems in this area. The patterns of hydrological drought in the Hexi Corridor were identified using the streamflow drought index(SDI) and standardized precipitation index at 12-month timescale(SPI12) from 1960 to 2013. The evolution of drought was obtained by the Mann–Kendall test and wavelet transform method. The results showed that both the mean annual SDI and SPI12 series in the Hexi Corridor exhibited an increasing trend during the study period. According to the results of wavelet analysis, we divided the study period into two segments, i.e. before and after 1990. Before 1990, the occurrence of droughts showing decreased SDI and SPI12 was concentrated in the northern part of the corridor and shifted to the eastern part of the corridor after 1990. The probability of drought after 1990 in Shule River basin decreased while increased in Shiyang River basin. The wavelet analysis results showed that Shiyang River basin will be the first area to go through the next drought period. Additionally, the relationships between drought pattern and climate indices were analyzed. The enhanced westerly winds and increased precipitation and glacier runoff were the main reasons of wet trend in the Hexi Corridor. However, the uneven spatial variations of precipitation, temperature and glacier runoff led to the difference of hydrological drought variations between the Shule, Heihe and Shiyang River basins.
