水分生产率是评价农业灌溉用水管理水平和节水效果的一个重要指标。本文用遥感数据定量估算流域平原区的蒸 散量和干物质量，采用经验的收获指数计算了海河流域2003年—2008年多年平均水分生产率。通过对水资源三级分区的统 计结果分析得出：遥感估算的水分生产率可以反映单方水产出的空间差异。海河流域平原平均水分生产率为0.99 kg/m3， 变化范围为0.02—2.13 kg/m3，总体水平较低，南北差异较大。通过ET，产量和水分生产率关系的分析表明：水分生产率 与产量线性相关(R2=0.97)，提高产量将一直是流域提高水分生产率的重要研究方向。水分生产率与产量随ET变化均呈现 先线性增加后减小的特点，在两季作物区当年耗水量在335—575 mm范围变化时，水分是影响产量和水分产出效益的关键 因子，要着重提高中低产区域的水分生产率。当耗水量超过575 mm时，水分就不是唯一的限制因子，而以提高作物的收获 指数为重点。

Agricultural water productivity is an important indicator to assess the effect of irrigation water management and water conservation. In this paper, a method is presented to calculate water productivity based on evapotranspiration (ET) and dry matter (DM) estimated by remote sensing data. Water productivity data are calculated and analyzed in the plain of Hai Basin from 2003 to 2008. The results show that water productivity data estimated by remote sensing can reflect spatial differences in the amount of water output per cubic meter. The average water productivity for the plain of the Hai Basin is 0.99 kg/m3, the range is 0.02—2.13 kg/m3, and the overall level is low with a big difference between north and south. The relationship between yield and water productivity shows a high linear correlation (R=0.97), and increasing yield production remains an important direction for improving the water productivity level in the basin. The curves between water productivity change with ET and yield changes with ET are similar, keeping stable after a linear increasing trend. When the water consumption of the wheat-and-maize rotation region is between 335—575 mm, water is the main limiting factor for yield production. When water consumption is higher than 575 mm, the harvest index is another important limiting factor for yield production except available water.