Author(s): C. He; L. Zhang
Linked Author(s): Liyin Zhang
Keywords: No keywords
Abstract: Proper allocation of the limited water resources among competing uses is essential to ensure the welfare of human beings and the sustainability of ecosystems, especially in arid regions such as Northwest China. The Heihe River Watershed is the second largest inland river (terminal lake) in China, with a drainage area of 128,000 km 2. From the headwaters in the south to the lower reach in the north, the Heihe River Watershed physically consists of the Qilian Mountain, the Hexi Corridor, and the Alashan Highland. The Qilian Mountain is situated at the south of the watershed, with a peak elevation of 5,584 m. Located in the middle reach of the Heihe River Watershed, the Hexi Corridor hosts over 90%of the total agricultural oases in the watershed and supports more than 97 percent of the Heihe watershed’s nearly 2 million inhibits. North of the Hexi Corridor is the Alashan Highland, an extremely dry desert with an annual precipitation below 50 mm. Since the 1970s, the increased withdrawals for agricultural irrigation in the Hexi Corridor have depleted much of the river flows to the lower reach, endangering aquatic ecosystems, accelerating desertification, intensifying water conflicts between the middle reach and lower reach users. To mitigate the water conflicts, the State Council of China has issued a “Water Allocation Plan for the Heihe Watershed Mainstream” , mandating the allocation of 0.95billion (10 9) m 3 of water annually to the lower reach under normal climatic conditions for rehabilitation of downstream ecosystems. However, are the flows from the upper and middle reaches sufficient to deliver 0.95billion (10 9) m 3 of the water downstream annually? This paper adapted the Distributed Large Basin Runoff Model (DLBRM) to the Heihe River Watershed to gain an understanding of the generation of glacial/snow melt, surface runoff and groundwater in the mountainous upper reach, and distribution of evapotranspiration (consumptive water use) in the middle reach of the watershed. The DLBRM was calibrated over the period of 1978–1987 (a wet hydrologic period) for each of the 9,790 cells (cell size: 4-km 2) at daily intervals. The calibration shows a 0.696 correlation between simulated and observed watershed outflows. The ratio of model to actual mean flow was 1.023. Over a separate simulation period (1990–2000, a normal hydrologic period), the model demonstrated a 0.717correlation between simulated and observed watershed outflows, and the ratio of model to actual mean flow was 1.069. Simulation of the daily river flows for the period of 1990–2000 by the DLBRM shows that Qilian Mountain in the upper reach produced most of the runoff in the watershed. Annually, the simulated average annual flow for 1990–2000 was about 0.896×10 9 m 3 from the middle reach to the lower reach under a normal, median precipitation year (P=50%), which falls short to meet the requirement of delivering 0.95×10 9 m 3 downstream annually mandated by the State Council 50 percent of the time. Under drier climatic conditions, even less amount of flow would be delivered downstream, posing an even greater challenge for restoring downstream ecosystem services. To tackle the increasing water conflicts among the upper, middle, and downstream users, we suggest that stakeholders from different levels of governmental agencies and private institutions be fully engaged in the watershed management process to develop a water allocation system that consists of multiple water allocation criteria, implementation plan, evaluation and feedback mechanisms.
Year: 2016