基于METRIC模型的巴基斯坦农业区蒸散量估算

Estimation of evapotranspiration in agricultural areas of Pakistan based on the METRIC model

  • 摘要: 蒸散量是水分循环和能量循环的重要载体, 精确估算农田蒸散量对农业水资源管理具有重要意义。巴基斯坦农业区是世界上重要的灌溉农区之一, 如何基于遥感技术估算区域实际蒸散量成为农业水资源精细化管理的基础和前提。本文利用MODIS数据、气象数据以及DEM数据, 采用METRIC模型, 估算了2019—2020年巴基斯坦农业区的实际蒸散量, 并分析了不同作物生育期蒸散量的时空分布特征, 以期为巴基斯坦农业水资源合理利用提供科学依据。研究结果表明: 1) 比较基于METRIC模型在日尺度和月尺度的蒸散估算结果与农业站点蒸渗仪的实际观测数据发现, 二者的均方根误差分别为1.2 mm∙d−1和25 mm∙month−1, 相关系数分别为0.65和0.84; 在空间上, 与ETMonitor产品比较, METRIC模型估算结果的空间分布和量级更为合理。2)巴基斯坦农业区蒸散量的空间分布与种植结构密切相关, 蒸散量自北向南总体呈阶梯递减格局, 小麦、棉花、水稻和甘蔗生育期累积蒸散量分别为392 mm、652 mm、745 mm和1224 mm; 就同一种作物来说, 旁遮普省作物生育期累积蒸散量高于信德省。3)小麦生育期内月蒸散量呈先下降再上升后下降的变化特征; 旁遮普省棉花生育期内月蒸散量呈“单峰”变化特征, 信德省棉花生育期内月蒸散量呈“双峰”变化特征; 水稻和甘蔗生育期内月蒸散量呈“单峰”变化特征。本研究实现了METRIC模型在巴基斯坦农业区的参数本地化应用和适用性分析, 为基于遥感手段估算区域或农作物尺度蒸散量提供了方法借鉴, 对揭示不同作物蒸散耗水的时空特征和区域农业水资源管理具有重要意义。

     

    Abstract: Water depletion in irrigated agriculture is recognized as a major cause of water scarcity. For agricultural water resource management, the precise measurement of field evapotranspiration is critical because it plays a critical role in both energy and water cycles. As one of the major irrigation regions in the world, Pakistan’s agricultural areas necessitate the accurate calculation of actual evapotranspiration using remote sensing technology for more advanced agricultural water resource management. This study estimated the real evapotranspiration in the agricultural areas of Pakistan during 2019–2020 using MODIS, meteorological and digital elevation model (DEM) data and the METRIC model. This study analyzed the spatiotemporal distribution patterns of evapotranspiration throughout several crop growth stages to present empirical evidence supporting the prudent use of agricultural water resources in Pakistan. 1) Using lysimeters to compare the METRIC estimation results with the data from agricultural stations, the correlation coefficients were found to be 0.65 and 0.84 at daily and monthly scales, respectively, with root mean square errors of 1.2 mm∙d−1 and 25 mm∙month−1, respectively. Additionally, comparing METRIC estimation findings with ETMonitor products at the spatial scale showed that the former were more accurate. 2) In the agricultural areas of Pakistan, the planting structure was directly associated with the spatial distribution of evapotranspiration, which decreased progressively from north to south. For wheat, cotton, rice, and sugarcane, the evapotranspiration were 392, 652, 745, and 1224 mm, respectively, for the whole growth season. The rate of evapotranspiration in Punjab Province was higher than that in Sindh Province for the same crop during the growth season. 3) Throughout the growing season, wheat showed a pattern of monthly evapotranspiration that initially decreased, then increased, and finally decreased. The growth period observed for cotton showed a “bimodal” monthly evapotranspiration pattern in Sindh Province, and a “unimodal” monthly evapotranspiration pattern in Punjab Province. During the growth season, the monthly evapotranspiration patterns of rice and sugarcane were “unimodal”. In addition to providing a methodology for crop-scale or regional evapotranspiration estimation based on remote sensing, this study achieved the localization and applicability analysis of the METRIC model in Pakistan agricultural areas. This is significant because it reveals the spatial and temporal characteristics of evapotranspiration and water consumption of various crops and helps manage regional agricultural water resources.

     

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