半干旱区沙丘、草甸作物系数模拟及蒸散发估算

Crop coefficient simulation and evapotranspiration estimation of dune and meadow in a semiarid area

作物系数(Kc)对提高实际蒸散量的估算精度及区域水资源调控具有重要意义。通过Landsat 8数据计算归一化植被指数(NDVI)、土壤调整植被指数(SAVI)和简单比值植被指数(SR),结合2017年地面实测土壤含水量(SM)和叶面积指数(LAI),通过逐步回归分析建立科尔沁地区草甸及沙丘试验区的作物系数估算模型,利用2018年模拟作物系数值与FAO 56 P-M模型计算所得潜在蒸散量(ET0)相乘,得到实际蒸散量(ETa)的估算值,与涡度相关系统所测实际蒸散量进行对比验证。结果表明:(1)草甸和沙丘试验区的作物系数在生长季内的变化趋势与植被指数及SM具有一致性,说明了基于这些指标建立Kc估算模型的可行性;(2)相关性分析中,草甸试验区的Kc与SR相关性不显著(P>0.05),沙丘试验区Kc与SR相关性较低(0.46),故剔除该因子;(3)逐步回归分析中进一步剔除不显著因子后建立草甸及沙丘作物系数估算模型,模型的均方根误差、修正的决定系数分别为0.06、0.84和0.12、0.71;(4)经涡度相关数据验证,基于Kc估算模型计算的ETa在草甸和沙丘试验区均取得较好的模拟效果。

The crop coefficient is of great significance for improving the estimation accuracy of the actual evapotranspiration and the regulation of regional water resources.In this paper,based on the Landsat 8 data extraction,we use three vegetation indices,normalized difference vegetation index(NDVI),soil adjusted vegetation index(SAVI),and simple ratio vegetation index(SR),combined with the ground measured soil moisture(SM)and the leaf area index(LAI)data in 2017.We then use the stepwise regression analysis to establish a crop coefficient Kc estimation model for the meadow and dune experimental area in the Horqin area.The simulated evapotranspiration(ETa)is obtained by multiplying the simulated Kc value and the potential evapotranspiration(ET0)calculated by the FAO 56 PM model in 2018.The accuracy of the Kc estimation model was verified by comparing it with the actual evapotranspiration(ETa)measured by the eddy covariance system.The results showed that the variation trend of Kc in the meadow and dune experimental area during the growing season was consistent with VIs and SM,indicating that it was feasible to establish a Kc estimation model based on these indicators.In correlation analysis,the correlation between Kc and SR in the meadow experimental area was not significant,whereas the correlation between Kc and SR in the dune experimental area was low.In the stepwise regression analysis,the insignificant factors were further removed,and the crop coefficient estimation model of meadow and dune was established;Radj2 was 0.84 and 0.71.The ETacalculated on the basis of the Kc estimation model achieved good simulation results both in the meadow and dune experimental areas.