基于植被遥感信息的作物蒸散量估算模型——以华北平原冬小麦为例

Modeling crop evapotranspiration using remotely sensed vegetation data: A case study of winter wheat in the North China Plain

本文基于作物系数法并结合植被遥感信息(MODIS/NDVI),提出一种能反映作物空间分布和土壤供水差异信息的作物蒸散量估算模型。利用该模型得到2000—2013年华北平原冬小麦的蒸散量,模拟结果与遥感蒸散产品吻合度较高(R2=0.952,RMSE=1.3×107 m3),并分析了冬小麦蒸散量和灌溉耗水量的时空变化。结果表明:1华北平原冬小麦蒸散量呈南高北低的格局。基于250 m空间分辨率上来看,山东省、河南省的黄河灌区以及太行山前平原的冬小麦蒸散量可达400 mm以上,中部平原区冬小麦蒸散量<350 mm,滨海一带蒸散量<200 mm。2冬小麦灌溉耗水量与其蒸散量格局相一致。在太行山前平原、河南省和山东省的引黄灌区,灌溉耗水量可达250 mm以上;河北平原北部由于冬小麦种植比例较低,灌溉耗水量<100 mm。3近14年河北平原北部冬小麦播种面积下降明显,区域灌溉耗水量减少,地下水位下降趋势得到明显缓解。本文提出的作物蒸散量估算模型能够较好地用于确定较大区域作物蒸散耗水量,并可应用于区域作物灌溉量的评估与管理中。

The North China Plain （NCP） is a vital granary of China, with an area of 140 000 km2 of arable land which produces some 20% of the nation＇s grain. As local precipitation is not enough to meet crop water requirements in the NCP, irrigation is widely used to increase yields and to ensure food supply. Agriculture accounts for about 70% of water consumption in the NCP, over 75% of which is from groundwater. Groundwater resource has steadily been depleted due to persistent over-pumping, posing tremendous challenges for sustainability. Meanwhile, excessive use of groundwater has resulted in severe environmental problems in the region. Thus, in order to achieve sustainable agricultural water management in the NCP, it is extremely important to explicitly estimate crop evapotranspiration in recent decades. In this paper, a model based on crop coefficient and vegetation remote sensing data was developed to estimate crop evapotranspiration in the NCP. The model not only estimated crop evapotranspiration, but also the spatial distribution of crops and soil moisture in the region. Moreover, the model was applicable to other studies such as water use efficiency and estimation of water footprint. With the model, winter wheat evapotranspiration was estimated for 2000？2013 in the NCP. The results of the model were consistent with those of ETWatch, a remote sensing evapotranspiration estimation product （R^2=0.952, RMSE=1.3×10^7 m^3）. The results were as follows： 1） Winter wheat evapotranspiration was higher in the southern than in the northern region of the NCP. Evapotranspiration was in excess of 400 mm in the piedmont region of Taihang Mountains and in the irrigation region of Henan-Shandong Yellow River. It was less than 350 mm in the middle plains and even less than 200 mm in coastal areas. 2） Irrigation water consumption by winter wheat was higher in the southern than in the northern region of the NCP. Irrigation was in excess of 250 mm in the piedmont region of Taihang Mountains and in the irrigation region of Henan-Shandong Yellow River. It was less than 100 mm in northern Hebei Plain. 3） There was a significant declining trend in the cultivated area of winter wheat and in irrigation water consumption in northern Hebei Plain in recent 14 years. Along with declining irrigation water consumption was also the slowing in the downward trend in regional groundwater level. Thus the effect of water-saving on the regional groundwater level was obvious. The proposed model in this study was applicable in estimating regional crop water consumption and irrigation water management.