实测草坪蒸散量评价P-M模型在北京地区适用性

为了研究北京地区的参考作物蒸散(reference evapotranspiration,ET0)特征以及Penman-Monteith(P-M)模型的适用性,2012-2014年生长季,应用蒸渗仪实测了冷季型高羊茅(Festuca arundinacea)、暖季型野牛草(Buchloe dactyloides)和乡土草种青绿苔草(Carex leucochlora)3种草坪的蒸散,应用自动气象站监测了试验地的太阳辐射、温度、空气相对湿度、风速等气象参数,通过P-M模型计算获得了ET0。将同期的P-M模型计算值与实测值进行了不同天气以及不同尺度下的比较分析,应用线性回归斜率与决定系数(R2)以及均方根误差(root mean square error,RMSE)与一致性指数(d)等统计参数进行了一致性评价。结果表明,P-M模型计算ET0与实测值在日、周、月尺度上均呈现一致的变化趋势。北京地区ET0高峰出现于5月,蒸散速率分别为4.18±0.27(P-M模型)、4.43±0.98(高羊茅)、3.96±0.23(青绿苔草)、3.53±0.25 mm/d(野牛草),10月最低。P-M模型计算的ET0与太阳辐射、平均气温、最高气温均呈极显著的线性关系,其中ET0与太阳辐射回归的R2最高,达到0.885。天气影响P-M模型的准确性,P-M模型计算ET0与草坪实测值的比值随着太阳辐射的降低(从晴天到雨天)而升高。P-M模型高估了阴雨天下的ET0。P-M模型计算ET0与实测值的RMSE和d值均随评价尺度减小而增大。实测ET0在3种草坪间差异显著,高羊茅青绿苔草野牛草。P-M模型计算ET0与高羊茅实测值的一致性最高,具有接近1.0的回归方程斜率(0.99~1.03)、最小的均方根误差(0.62~1.05 mm/d)和最高的一致性指数(0.89~0.90)。P-M模型在北京地区有较好的适用性,但在阴雨天气及春季低温情况下会高估ET0。

Suitability assessment of P-M model by measuring ET0 of turfs in Beijing, China

Abstract: Reference evapotranspiration (ET0) is an important parameter for agricultural irrigation scheme. Penman-Monteith (P-M) model is used extensively to simulate ET0 for its accuracy in Europe and America area. But it''s rarely evaluated by lysimeter measurement in China. This study aimed to: 1) reveal ET0 characteristics in Beijing area; 2) evaluate the accuracy of P-M model under different weathers and at different scales; 3) research the effect of plant species on ET0 measurement and P-M model evaluation. The evapotranspiration of the cool-season grass Festuca arundinacea, the warm-season grass Buchloe dactyloides, and the native species Carex leucochlora during the growing seasons of 2012-2014 was measured by lysimeters. Meteorological parameters of the solar radiation, the temperature, the air relative humidity, and the wind speed were measured using a weather station and were put into P-M model to obtain ET0 values. Comparison was conducted between the P-M calculated ET0 and the measured values under different weather conditions and at different scales. The consistency was analyzed using the statistical parameters of the slope and the coefficient of determination (R2) of the linear regression, the root mean square error (RMSE), and the consistency index (d). The results indicated that the calculated ET0 showed consistent trends with the measured values at all the daily, weekly, and monthly scales. The peak of the monthly ET0 came in May, with the values of 4.18±0.27 (P-M), 4.43±0.98 (F. arundinacea), 3.96±0.23 (C. leucochlora), 3.53±0.25 mm/d (B. dactyloides). October had the lowest value. The monthly calculated ET0 showed a significant linear relationship with the solar radiation, the average air temperature, and the highest air temperature (P<0.01). The regression between ET0 and the solar radiation had the highest R2 of 0.885. The ratio of the calculated ET0 to the measured value varied with different weathers. It increased with the solar radiation decreasing from the sunny to the rainy day. The P-M model overestimated ET0 under overcast and rainy weathers. The RMSE and d between the P-M calculated ET0 and the measured values increased with the assessment scale decreasing. The measured ET0 differed significantly, sorted by F. arundinacea > C. leucochlora > B. dactyloides. The calculated ET0 was the highest consistent with the measured value of F. arundinacea, with the regression slope of 0.99-1.03, the lowest RMSE of 0.62-1.05 mm/d, and the highest d of 0.89-0.90. It''s concluded that P-M model was applicable for Beijing area. But it could overestimate ET0 under overcast and rainy weathers or in cold spring.