四川省潜在蒸散量估算模型

Penman-Monteith法是FAO-56推荐的计算潜在蒸散量的标准方法, 但由于涉及的气象要素较多, 难于在业务中应用。以综合气象干旱指数的业务化应用为目标, 利用1971-2000年四川省156个气象站的观测资料, 以Penman-Monteith法计算结果作为标准,分析了Thornthwaite法和Hargreaves法对川西高原和四川盆地年、月潜在蒸散量的估算精度, 建立了可供业务应用的E_T0估算模型, 并应用于2006年四川省特大伏旱监测, 结果表明:Thornthwaite法反映不出E_T0的年际变化,在冬季显著偏小, 而Hargreaves法对E_T0的年际变化具有较好的反映能力, 与Thornthwaite法相比,其E_T0年、月估算值更接近于Penman-Monteith法标准值,且Hargreaves法估算值与Penman-Monteith法标准值之间具有较好的线性关系,引入风速和相对湿度两个订正因子后,Hargreaves订正值的误差可控制在10%以内, 基于该文E_T0估算模型计算的综合气象干旱指数对四川干旱具有较强的监测能力。

Estimation Models of Potential Evapotranspiration in Sichuan Province

Penman-Monteith formula is a standard method recommended by FAO-56 to calculate potential evapotranspiration.But it is difficult to apply in practical operation as not all related meteorological elements can be obtained in reality,so estimation models are used instead.In order to apply compound drought index in operation,Thornthwaite method and Hargreaves method for yearly and monthly potential evapotranspiration of Sichuan Basin and West Sichuan Plateau are studied.The observation data of 156 meteorological stations in Sichuan Province from 1971 to 2000 are investigated including minimum temperature,maximum temperature,wind speed,relative humidity,and sunshine hours.Using result of Penman-Monteith formula as the E_(T0) standard value,the precisions of the two T_(T0) estimation methods are analyzed.Comparing wind speed,relative humidity,Hargreaves method and Penman-Monteith method statistically,an operational Hargreaves method is established.These Hargreaves method and model have been applied to monitor serious summer drought in 2006 in Sichuan Province.The results show:As far as annual variation is concerned,annual value fluctuation estimated by Thornthwaite method is small so that it cannot reflect the E_(T0) annual variation.However,Hargreaves method and PM method show basically consistent changing tendency and can reflect the E_(T0) annual variation characteristics better. As for the annual mean,result of Thornthwaite method is significantly smaller. The error in the Basin is -10%--20% and -40%-- 60% on Plateau.Result of Hargreaves method is relatively smaller in Plateau and larger in Basin.But its error is 10%-15% ,better than Thornthwaite's.As for the seasonal variation,error of Thornthwaite method is larger in winter but smaller in summer.Due to the influence of relative humidity and wind speed,seasonality of Hargreaves method's error is not obvious.The error of Hargreaves is smaller than that of Thornthwaite especially in Plateau region except for in summer.Results of Penman-Monteith formula and Hargreaves method show good linear relation.With the recovery factors air velocity and relative humidity introduced,the error of Hargreaves correction value can be controlled within 10%.It can meet the demand of practical operation for precision.The compound drought index calculated by this E_(T0) estimation model has strong capability for drought monitoring in Sichuan Province.