基于水足迹与虚拟水的灌区种植结构开放式优化与模拟

The planting structure planning according to water resource endowments is the structural reform of agricultural supply-side in drylands and an important measure to improve total factor productivity.The planting structure in China has changed significantly in recent years, but due to lack of appropriate optimization method and assessment indices, old methods of planting structure optimization are not able to comprehensively consider the optimal integrated utilization of both irrigation and rainfall water and to realize the coordination of comparable advantages of crop water productivity inside and outside a given region.The development of water footprint and virtual water theory provides a new approach to deal with the issue. This study takes the Hetao Irrigation District, a typical large-scale irrigation district in arid northwest China, as an example to establish a new optimization method of planting structure. The objectives of this work are: 1) to explore the internal mechanism of crop-structure evolution driven by the conflict between reduction of the regional crop water footprint and increase of grain virtual water flows,based on the analysis of coupling properties of crop-structure evolution, crop production water footprint, and virtual water flows in the past 50 years; 2) to establish an open multi-objective optimization model for water-saving planting structure by setting crop production water footprint as an evaluation index and virtual water flows as adjustment parameters; and 3) to realize the transformation of planting structure adjustment from local optimization in a given region to global optimization in overall consideration of both inside and outside of a specific region, and to solve the problem that current closed optimization methods had not been widely applied since they did not take into account the strategic problem of food security in China.

种植结构适水性调整是缺水地区农业供给侧结构性改革，提高全要素生产率的重要措施。近年来我国种植结构变化明显，但因缺乏适宜的评价指标与方法，已往种植结构优化难以统筹考虑灌溉水和降水的综合最优利用，以及区域内外作物用水效率比较优势的协同，水足迹与虚拟水理论的提出，为解决这一难题开辟了新途径。本研究以西北旱区的河套灌区为例，揭示近50年来种植结构演变和作物生产水足迹、虚拟水流动的耦合特征，剖析种植结构变化主要受降低作物生产水足迹和增加粮食虚拟水流动这一矛盾共同驱使的内在本质，进而以作物生产水足迹作为效率评价指标，以虚拟水流动为参数调节项，构建节水型多目标开放式优化模型，以实现种植结构调整由仅着眼于区域的局部最优向统筹考虑区域内外全局最优的转变，解决目前封闭式优化方法因未能兼顾国家战略粮食安全问题而难以推广应用的难题。研究对于促进我国北方灌区种植结构的良性发展，缓解区域水资源压力具有重要意义。

种植结构适水性调整是缺水地区农业供给侧结构性改革，提高全要素生产率的重要措施。近年来我国种植结构变化明显，但因缺乏适宜的评价指标与方法，已往种植结构优化难以统筹考虑灌溉水和降水的综合最优利用，以及区域内外作物用水效率比较优势的协同，水足迹与虚拟水理论的提出，为解决这一难题开辟了新途径。本研究以西北旱区的河套灌区为例，建立了灌区尺度作物生产水足迹与虚拟水流动计算方法，通过量化3类主要作物生产水足迹（产量、热量和价值水足迹），明确区域种植结构变化与农业用水效率和效益的关系；基于不同作物生产水足迹及作物贸易情景，揭示种植结构变化与作物虚拟水流动的耦合特征；对比分析不同作物水足迹的绝对比较优势和相对比较优势，构建考虑灌区内外协同优化的种植结构优化开放式博弈模型，模拟不同情景下种植结构优化调整方法及方案。获得的主要结果包括：灌区3类主要作物生产水足迹的年际变化明显，空间分布特征主要受区域农业生产水平影响；灌区作物生产灰水足迹占比为35%-40%，灌区种植结构调整应着重控制农业面源污染和提高农业用水的效率和效益；建立的开放式优化模型有助于实现种植结构调整向统筹考虑区域内外全局最优的转变；种植结构优化有助于保障灌区粮食安全、生态安全，提高经济效益、水分利用效率和绿水使用比例；优化后灌区作物所能提供的能量值提高了1倍，灰水足迹降低了29%，水分利用效率降低了6%，绿水占比提高了2%；农户意愿对种植结构调整的顺利实施尤为重要，政府和灌区管理单位需要在文化教育、粮食和农机补贴、农产品保护价控制方面来增强农户抵抗风险的能力。研究成果对于促进我国北方灌区种植结构的良性发展，缓解区域水资源压力具有重要意义。

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