干旱区生态环境知识资源中心

Oases are of great importance to the sustainable development of economies and societies in desert regions. Thus, it is important to understand how many oases have survived for hundreds and even thousands of years. Oases in Northwest China include nearly all of the types found across the world. Among these oases, the Minqin Oasis, surrounded by mobile sandy deserts, is a stereotypical natural oasis that has been developed for more than 2000 years, making it ideal for a case study. Our investigation indicates that the nebkhas belt at the fringe of the Minqin Oasis, which consists of three sub-belts semi-mobile, semi-fixed and fixed nebkhas from desert to the oasis, plays a key role in its stability. The fractional speed-up ratio (delta(s)) of wind generally fell within the range of -0.15 to -0.55 below the height of 0.6 m. Above the height of 0.6 m, wind velocity in the semi-mobile nebkhas was 5-27% weaker with a maximum reduction of 65% in the other two sub-belts. When wind carrying sand and dust from the desert passes through each sub-belt, its velocity is weakened by vegetation and dunes, and almost all sand and dust is deposited in the nebkha belt incrementally by grain size, ranging from coarse to fine. As such, nebkhas serve as a protection belt and ensure the existence of oases. (C) 2015 Elsevier B.V. All rights reserved.