作物最大可能蒸散考虑了作物及当地地表状况,为当地地表实际覆盖情况下实际蒸散的理论上限值,能客观分析作物对水分的需求程度和农业干旱状况.基于遥感(叶面积指数和地表反照率)数据和逐日气象数据,利用Penman-Monteith公式,计算黄淮海平原小麦种植区27个气象站冬小麦生育期2000-2015年逐日蒸散,提取得到冬小麦生育期逐日最大可能蒸散数据集,并分析其时空变化特征及成因.结果表明:与联合国粮农组织(FAO)单作物系数法计算的最大可能蒸散Ek对比,区域平均最大可能蒸散Ec的时间变化趋势与Ek一致,空间分布上Ec符合客观实际.黄淮海平原冬小麦全生育期、越冬期和返青-拔节期Ec均呈北低南高的分布特征,日平均值分别为1.99 mm,0.44 mm和2.75 mm;其余3个生育期(越冬前、抽穗期、乳熟-成熟期)在空间分布上差异不大,日平均值分别为1.23 mm,4.71 mm和3.74 mm.冬小麦不同生育期(含全生育期)Ec的空间分布主要受叶面积指数分布特征的影响,二者呈显著正相关关系.%Crop evapotranspiration under standard conditions (Ec) is defined as the evapotranspiration from disease-free,well-fertilized crops grown in large fields,under optimum soil water conditions,and achieving full production under the given climatic conditions.The calculation of Ec considers crop and local surface conditions.Ec is the theoretical upper limit of actual evapotranspiration for actual local surface coverage,ensuring objective analysis on crop water requirements and agricultural drought.To summarize the spatial and temporal distribution characteristics and their causes of Ec,daily Ec is calculated based on PenmanMonteith method using meteorological data and satellite remote sensing data from 2000 to 2015.The meteorological data are provided by 27 meteorological stations in the winter wheat growing area of the HuangHuai-Hai Plain.The satellite remote sensing data are extracted from NASA MODIS products (LAI (MOD15A2) and Albedo (MCD43C3)) at the corresponding location of 27 meteorological stations.Ek is calculated based on single crop coefficient approach recommended by FAO.Results show that daily dynamic changes of Ec and Ek are consistent in the regional tie scale.However,compared with Ek,Ec has a spatial distribution corresponding to the objective reality.The growth period of winter wheat is divided into five stages:Before wintering stage,wintering stage,returning green-jointing stage,heading stage and milky maturity-maturity stage.With the spatial distribution characteristic of higher in the south and lower in the north,the average daily Ec in the whole winter wheat season,wintering stage and returning greenjointing stage is 1.95 mm,0.46 mm and 2.74 mm,respectively.The average value of Ec is 1.23 mm before wintering stage,and the whole fluctuation of Ec in the Huang-Huai-Hai Plan is small.There is no significant fluctuation in Ec in heading stage and milky maturity-maturity stage except for the middle part of the Huang-Huai-Hai Plain.The average value of Ec is 4.71 mm and 3.72 mm in these two growth stages,respectively.In terms of spatial distribution,extremely significant positive correlation is shown between LAI and Ec in all growth periods.In wintering stage,returning green-jointing stage and milky maturitymaturity stage,Ec also shows a higher significant negative correlation with albedo.During the whole growth period of winter wheat,Ec has a higher partial correlation coefficient with LAI and water vapor pressure.These results can provide basic data for drought monitoring and wet or dry climate zoning in China,and also provide a new idea for the actual evapotranspiration estimation.
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