基于SIMDualKc模型估算西北旱区冬小麦蒸散量及土壤蒸发量

为研究西北旱区冬小麦蒸散和土壤蒸发规律,以及土壤蒸发比例与其影响因子的关系,利用2 a冬小麦小区控水试验实测数据,对SIMDual Kc模型进行了参数校正和验证,对比大型称重式蒸渗仪的实测蒸散量值(或水量平衡法计算值)与模型模拟值。用建立的模型模拟精度评价标准对模拟值和实测值的误差进行评价。用经参数校验的模型模拟冬小麦农田土壤蒸发,并与微型蒸渗仪的实测值进行对比。基于通径分析方法研究气象因子(最低气温、最高气温、平均相对湿度、2 m处风速、太阳辐射量)和作物因子(地面覆盖度)与土壤蒸发比例的关系。结果表明,该研究建立的模型模拟精度评价标准能够较为全面地评价模型精度;SIMDual Kc模型可以较好地模拟西北旱区不同灌溉制度下冬小麦蒸散量和土壤蒸发量的变化过程,且在模拟长时段累积值时具有较高精度;拔节-灌浆期是冬小麦的需水关键期,冬小麦全生育期土壤蒸发比例呈现出生长中期生长后期快速生长后期生长初期的规律;灌水仅在短时间内影响土壤蒸发,地面覆盖度是影响土壤蒸发的最主要因子;在实测数据不充足的情况下,可以将地面覆盖度和蒸散量作为输入变量,用该研究确定的土壤蒸发比例与地面覆盖度的回归模型计算土壤蒸发量,该模型在计算不同水分条件下冬小麦农田土壤蒸发量时表现出较高的计算精度,决定系数在0.721~0.902之间,可以作为计算土壤蒸发量的简便方法。研究可为西北旱区冬小麦农田节水和灌溉决策提供理论依据。

Estimation of evapotranspiration and soil evaporation of winter wheat in arid region of Northwest China based on SIMDualKc model

Abstract: Crop evapotranspiration (ETC) consists of transpiration and soil evaporation. It is important to know the proportion of transpiration and soil evaporation in field of agricultural water saving. The dual crop coefficient approach can calculate transpiration and soil evaporation by dividing a crop coefficient (Kc) into a basal crop coefficient (Kcb) and a soil evaporation coefficient (Ke). In this study, we used SIMDualKc model, a computer model developed by using the theory of dual crop coefficient approach, to calculate evapotranspiration and soil evaporation of winter wheat under different irrigation schedules in arid region Northwest China. Before modeling, a 2-year water-controlled experiment of winter wheat was conducted to calibrate and validate SIMDualKc model. Evapotranspiration was observed by a large-scale weighing lysimeter or calculated by water balance approach, and soil evaporation in 2013-2014 was measured by a micro-lysimeter. We compared the observed evapotranspiration and soil evaporation with the simulated ones. The regression coefficient (b), determination coefficient (R2), root mean square error (RMSE), average absolute error (AAE), Nash-Sutcliffe efficiency (NSE), RMSE-observations standard deviation ratio (RSR) and index of agreement were used to evaluate the errors between observed and simulated evapotranspiration and soil evaporation. The results showed that the SIMDualKc model could accurately simulate evapotranspiration and soil evaporation of winter wheat under different irrigation schedules. Modeling result showed that the key water requirement period of winter wheat was from jointing to grain filling stage, and the soil evaporation ratio in the whole winter wheat growth stage was highest in the mid season stage, followed by the late season stage, crop development stage, and initial stage. On the basis of the simulation, we investigated the relationship between soil evaporation ratio and meteorological factors (minimum temperature, maximum temperature, average relative humidity, wind speed at 2 m above ground surface, solar radiation), and crop factor (ground surface coverage) by using the path analysis method. The result showed that the irrigation only affected soil evaporation in a short period, while ground surface coverage affected it most in a long period with a total indirect influential coefficient of -0.857. A regression model of soil evaporation ratio and ground surface coverage was developed by using the soil evaporation ratio simulated by SIMDualKc model and the ground surface observed in the field experiment. The regression model could accurately calculate soil evaporation of winter wheat under different water conditions with determination coefficients 0.721-0.902 and it could be used as a simplified method to calculate soil evaporation. These findings confirmed that SIMDualKc model was a useful tool to study the change of evapotranspiration and soil evaporation under different irrigation schedules. The further study should focus on the integration of SIMDualKc model and other crop growth models.