黑河分水后张掖市水资源供需格局变化及驱动因素

A Study on Changes and Driving Factors of Agricultural Water Supply and Demand in Zhangye after Water Reallocation of the Heihe River

2002年起张掖市开始了节水型社会建设试点,以缓解黑河分水后张掖市可用水量减少的局面。本文通过分析张掖市水资源供需的时空变化及其影响因素,揭示了黑河分水后张掖市水资源供需格局变化的驱动因素及经济学机制。结果表明:建立水权制度、渠道衬砌等工程手段以及农业结构调整等节水型社会建设的措施对于实行"总量控制"、保障黑河分水的顺利实施发挥了积极作用。但目前水量向灌区分配时仍然比较粗放,"定额管理"也没有得到严格执行,超额灌溉的现象没有得到有效控制,剩余水量回购定价过低阻碍了水权交易。当前张掖市的水量平衡是在上游来水增加的条件下得以保持的,一旦上游来水减少,现行绿洲农业的规模和结构将难以为继,工业化、城市化的推进和生态建设将会面临水资源的制约,亟需重新思考绿洲农业的规模和发展模式,加强和完善农业用水需求管理。

In 2001, to ease ecological deterioration of the lower reach regions of the Heihe River, the Ministry of Water Resources decided to reallocate its water resources to increase the runoff of the lower reaches. In response to water shortage caused by the water reallocation, Zhangye City began its ＂water-saving society＂ construction to adapt to the situation of water shortage since then. By revealing changes in agricultural water supply and demand in Zhangye City after water reallocation and analyzing the driving factors of those changes, it is helpful to have a better understanding of why and how these policies and measures work, and give policy recommendations for sustainable development of Zhangye City in the future. First, we compared water supply data of years 2000, 2005 and 2008. Second, we estimated water demand of each sub-zone of those three years based on both statistical data and investigation data, and analyzed driving factors of changes in water demand. Through combining water supply and demand data, the water demand deficit of Zhangye City in 2000, 2005 and 2008 as well as water demand deficit under different probabilities of runoff were calculated. Results indicate that： 1） after the water reallocation, surface water of sub-zones in Ganzhou and Linze were decreased, whereas that of sub-zones in Gaotai were increased. Due to increasing water demand in Linze and Gaotai, more ground water were exploited in those sub-zones. 2） By substituting crops of high water intensity with seed maize, the irrigating quota per unit area decreased in Heihe and Liyuanhe sub-zones. On the contrary, the total quota of some sub-zones increased because of the increasing sown area. It is considered that the driving factor of this situation is farmers’ pursuit of higher expected returns which drove them to choose crops with higher profits or use extra water to increase their sown area. The reason why water right trade policy did not work well is that the water right was underpriced. 3） The current overall balance of water supply and demand relies on extra runoff from the upstream and exploiting more ground water. If the runoff decreased, the current scale and pattern of oasis agriculture in Zhangye City would face a potential water crisis, especially in the suburban sub-zones and mountain side sub-zones. 4） In the future, oasis agriculture would also face challenges of urbanization and industrialization on water resources. A serious consideration should be taken for the mode and scale of the development of oasis agriculture