地表水与地下水之间时刻发生着复杂的物质、能量交换，是水文循环的重要环节。宁夏引黄灌区地处西北干旱区，该地区降水稀少、蒸散发作用强烈，在以灌溉为主的人类活动影响下，伴随着下垫面条件的不断变化，地表水-地下水交互过程非常复杂，并由此衍生出了一系列水资源相关问题，灌溉引水供需矛盾尤其突出。高效节水政策背景下，为促进该地区水资源可持续发展，实现地表水-地下水协同管理，以宁夏河东灌区为研究区，在回顾国内外关于地表水-地下水相互作用关系研究进展的基础上，针对该灌区水循环系统协同演变复杂问题，采用SWAT-MODFLOW耦合模型，开展地表水-地下水联合模拟研究。首先基于SWAT构建了研究区水文模型，针对模型率定期与验证期拟合效果不一致问题，探索使用MDUPLEX算法，显著提高了模型在率定期与验证期的拟合效果及二者的一致性。进一步采用MODFLOW建立了研究区饱和地下水动力模型，实现了与率定后的SWAT模型动态耦合，并对耦合后的模型进行了识别与验证。基于SWAT-MODFLOW耦合模型，对灌区现状水循环响应规律以及用水效率进行分析评价，并以现状年为基准，围绕种植结构、灌溉方式、渠系衬砌等不同节水措施设置开展情景分析。现状年模拟结果表明，灌区地表-地下水循环关键要素均受灌溉影响强烈，且时空分布特征基本一致；地下水位随灌期动态变化，年内水位最大变幅为1.07 m，年际水位逐年降低，2010～2014年间累计降幅达0.22 m；现状年灌区地下水基本均衡，潜水补给以田间灌溉入渗和渠系渗漏为主，排泄以沟排和潜水蒸发为主，灌区现状引黄水排引比为50.72%。情景分析结果表明，在单一节水措施作用下，受田间灌溉入渗和渠系渗漏补给减少的影响，基于水平衡的地下水储量呈负增长，地下水位有所下降，引水量与耗水量均有减少，用水效率有所提升，其中以优化灌溉方式成效较为显著；而在综合节水措施的共同作用下，灌区能够实现极限节水，引水和耗水的最大节水率分别达41.02%、30.92%，最大节水潜力分别为4.82亿m3和1.79亿m3，且用水效率大幅提升，农业耗水率达57.72%，但同时也伴随着地下水位降幅达到最大值，约为0.76 m。本文揭示了河东灌区地表水-地下水交互转化关系及其演变响应规律，并对变化情景下的用水效率和节水潜力进行探究评价，为该研究区以及宁夏引黄灌区未来在节水背景下进行水资源综合管理提供理论依据。
Surface water and groundwater exchange mass and energy dynamically and continuously with each other, which is one of the most important sub-processes of the hydrological cycle. Located in the arid region of northwest China, the Ningxia irrigation area is characterized by sparse rainfall and intense evapotranspiration. Human activities (e.g., irrigation) and the continuous change of underlying surface make the interaction between surface water and groundwater can be very complex in this area, which gives rise to a series of water resources-related problems, for instance, the contradiction between supply and demand of irrigation water diversion. Under the circumstance of high-efficiency water-saving policies, we select the Ningxia Hedong Irrigation District as the study area and intend to promote the sustainable development of water resources and realize the synergistic management of surface-groundwater in this area. To this end, a SWAT-MODFLOW coupled model was developed to carry out a conjunctive simulation of surface water and groundwater.To build the conjunctive simulation model, a hydrological model was first constructed using SWAT. Besides, the MDUPLEX algorithm was adopted to address the inconsistent fitting effect between the model calibration period and validation period. Furthermore, the MODFLOW simulator was used to simulate the saturated groundwater movement. The MODFLOW model was further coupled with the calibrated SWAT model and was identified and validated using the trials and errors method. The results show that the key elements of the surface-groundwater hydrological cycle are strongly influenced by irrigation in the status quo year, and the spatial and temporal distribution is basically the same. Besides, the groundwater table fluctuant dynamically with the irrigation, and the maximum variation of the water level within the year is about 1.07 m. The water level has a decreasing tendency from 2010 to 2014, and the cumulative decrease can reach 0.22 m. The groundwater in the irrigation district is relatively balanced. The shallow groundwater is mainly recharged by field irrigation infiltration and canal leakage, while it is mainly discharged by drains and phreatic evaporation. The current ratio of drainage to diversion in the irrigation district is about 50.72%. The scenario results indicate that under the effect of the single water-saving measure, the groundwater storage shows a negative balance and the groundwater level tends to decrease. However, the water diversion and water consumption will be reduced, while the water use efficiency will be improved. The combined effect of comprehensive water-saving measures shows that the irrigation district can achieve extreme water savings, with maximum water-saving rates of 41.02% and 30.92% for diversion and consumption and maximum water-saving potentials of 482 and 179 million cubic meters, respectively. For this scenario, a significant increase in water use efficiency with an agricultural water consumption rate of 57.72% is witnessed, though accompanied by a maximum groundwater level decrease of 0.76 m.This paper reveals the transformational relationships and evolutionary response laws between surface water and groundwater in the Hedong Irrigation District. What is more, assessment of water use efficiency and water saving potential under different scenarios provides a theoretical basis for future integrated water resources management in the context of water-saving in this study area as well as the Ningxia Yellow Diversion Irrigation District.
