黄河中游旱作农业区粮食作物水足迹及其时空变化分析：以榆林市为例

Analysis of the water footprint and its spatiotemporal variation of grain crops in the dryland farming area of the middle reaches of the Yellow River: a case study of Yulin City

关键词:  粮食作物  水足迹  蓝绿水  用水效率  榆林市

Key words:  grain crops  water footprint  blue and green water  water use efficiency  Yulin City

摘要:

水资源短缺已成为制约黄河中游旱作农业可持续发展的关键因素。榆林市作为典型的资源性缺水区，其粮食作物耗水特征及用水效率问题亟需深入研究。文章以榆林市主要粮食作物玉米、大豆、水稻和小麦为研究对象，基于作物蒸散发模型和水足迹理论，系统分析了2000—2020年主要粮食作物生育期蒸散发特征、单位面积蓝绿水需水量及蓝绿水足迹的时空变化规律。结果表明：（1）不同作物蒸散发量差异显著，水稻蒸散发量最高，为775.60 mm，小麦最低，为468.77 mm，玉米和大豆分别为571.33 mm和609.99 mm，表明不同作物对水资源的依赖程度存在明显差异。（2）各作物单位面积蓝绿水需水量总体呈波动上升趋势，其中水稻单位面积蓝水需水量最高，达到6111.58 m³/hm²；各作物蓝水需水量均高于绿水需水量，反映出区域作物生产对灌溉水源依赖程度较高。（3）不同作物单位质量水足迹差异显著。玉米单位质量蓝水足迹最低（0.85 m³/kg），大豆最高（4.19 m³/kg）；水稻单位质量绿水足迹最低（0.25 m³/kg），仅为大豆（1.47 m³/kg）的17.0%。2000—2020年，玉米单位质量蓝水足迹略有下降，大豆和小麦下降趋势明显，而水稻略有上升；单位质量绿水足迹方面，玉米和水稻呈小幅上升趋势，大豆和小麦呈下降趋势。综合来看，玉米兼具较低的蓝绿水足迹和较高的水资源利用效率，是榆林市节水型农业发展的优选粮食作物。（4）2000—2020年，榆林市主要粮食作物蓝绿水足迹总量总体呈波动上升趋势。玉米始终占据主导地位，其蓝水足迹和绿水足迹峰值分别达到1.235×10⁹ m³和6.06×10⁸ m³；大豆蓝绿水足迹总体保持增长态势；水稻和小麦则呈下降趋势，其中小麦蓝水足迹由1.18×10⁸ m³下降至不足3×10⁵ m³。区域粮食作物蓝绿水足迹结构由多作物并存逐步演变为以玉米和大豆为主导的格局，表明农业种植结构逐渐适应水资源约束条件，耐旱型作物在区域农业生产中的优势地位不断增强。以上研究表明，在水资源刚性约束条件下，优化种植结构、优先发展玉米等高产低耗水作物，并持续推进节水灌溉技术应用，是提升区域农业用水效率和促进水资源可持续利用的重要途径。

Abstract:

Background, aim, and scope Water scarcity has become a key constraint on the sustainable development of dryland agriculture in the middle reaches of the Yellow River. Yulin City, a typical resource-deficient region, is characterized by low agricultural water-use efficiency and an irrational crop water-consumption structure. This study focuses on maize, soybean, rice, and wheat, and applies the water footprint framework combined with crop evapotranspiration modeling to systematically investigate crop water consumption characteristics, blue and green water demands, and the spatiotemporal evolution of water footprints from 2000 to 2020. The objective is to quantify inter-crop differences in water use and assess their impacts on regional water stress, providing a scientific basis for optimizing cropping patterns and improving agricultural water-use efficiency. Materials and methods The study employs the FAO Penman-Monteith equation and the dual crop coefficient approach to estimate crop evapotranspiration. By integrating multi-source datasets, including meteorological variables, soil properties, irrigation practices, crop yields, and planting areas, the blue and green water demands and water footprints of maize, soybean, rice, and wheat in Yulin City from 2000 to 2020 were systematically quantified. Spatiotemporal variations and differences in water-use efficiency among crops were further analyzed. Results (1) Significant differences in crop evapotranspiration were observed, with rice showing the highest value (775.60 mm) and wheat the lowest (468.77 mm), while maize and soybean exhibited intermediate values of 571.33 mm and 609.99 mm, respectively, indicating substantial variability in crop water demand. (2) Blue and green water demands per unit area exhibited an overall fluctuating increasing trend. Rice had the highest blue water demand (6111.58 m³/hm²), and blue water demand consistently exceeded green water demand across all crops, indicating a strong dependence on irrigation water. (3) Significant differences in water footprints per unit mass were identified. Maize exhibited the lowest blue water footprint per unit mass (0.85 m³/kg), while soybean showed the highest (4.19 m³/kg). Rice had the lowest green water footprint per unit mass (0.25 m³/kg), accounting for only 17.0% of that of soybean (1.47 m³/kg). From 2000 to 2020, maize showed a slight decline in blue water footprint per unit mass, soybean and wheat decreased markedly, while rice exhibited a slight increase. For green water footprint per unit mass, maize and rice showed slight increases, whereas soybean and wheat declined. Overall, maize demonstrated the highest water-use efficiency and represents a key crop for water-saving agriculture in the region. (4) Total blue and green water footprints of major crops in Yulin City showed an overall fluctuating upward trend from 2000 to 2020. Maize remained the dominant contributor, with peak blue and green water footprints reaching 1.235×10⁹ m³ and 6.06×10⁸ m³, respectively. Soybean showed an increasing trend, while rice and wheat declined, with wheat exhibiting the most pronounced reduction (from 1.18×10⁸ m³ to <3×10⁵ m³). The crop water footprint structure gradually shifted from a diversified pattern to a maize- and soybean-dominated system, reflecting an increasing adaptation of agricultural systems to water constraints. Discussion This study systematically reveals differences in evapotranspiration, blue and green water demands, and water footprints among major crops in Yulin City, highlighting significant disparities in water dependence and water-use efficiency. Rice exhibits the highest water demand and strongest irrigation dependence, whereas maize shows relatively low blue water footprints and high-water productivity, making it suitable for cultivation in water-scarce regions. Soybean and wheat exhibit improved water-use efficiency over time due to technological progress, while rice shows a declining trend. Overall, blue water demand exceeds green water demand across all crops, indicating that irrigation remains the dominant component of agricultural water use. From 2000 to 2020, total water footprints exhibited a fluctuating upward trend, accompanied by a shift toward drought-tolerant crops such as maize and soybean, reflecting adaptive adjustments of the agricultural system under increasing water constraints. However, several limitations remain, including limited spatial and temporal resolution of data, exclusion of grey water footprints and extreme climate scenarios, and uncertainties introduced by parameter simplification. Conclusions This study reveals significant inter-crop differences and temporal dynamics in blue and green water use in Yulin City. Rice shows the highest evapotranspiration and water demand, while maize exhibits the lowest blue water footprint and highest water-use efficiency. Overall, blue water demand exceeds green water demand, indicating strong irrigation dependence in agricultural production. From 2000 to 2020, total water footprints show a fluctuating increasing trend, with a gradual shift toward maize and soybean dominated cropping systems, reflecting increasing adaptation to regional water scarcity. Recommendations and perspectives Future research should focus on the coupled effects of climate change and human activities on the evolution of blue and green water resources and their feedback mechanisms with food production and ecological conservation, while enhancing the integration of multi-source observational data and numerical models, as well as multi-scale coordinated management approaches, to improve the simulation accuracy and decision-support capacity for sustainable water resource management in arid and semi-arid regions. Future research should incorporate high-resolution datasets and multi-scenario modeling to improve the robustness of water footprint assessments.