四川省不同区域参考作物蒸散量计算方法的适用性评价

Adaptation evaluation for reference evapotranspiration methods in different regions of Sichuan

为实现参考作物蒸散量（reference crop evapotranspiration,ET0）在资料缺失情况下的准确计算,对ET0简化算法在四川省不同区域的适用性进行科学评价,将四川省划分为4个区域（I东部盆地区、II盆周山地区、III川西南地区和IV川西高原区）,采用46个气象站点1954-2013年逐日气象资料,以1998 FAO-56 Penman-Monteith（PM）法的计算结果为标准,对具有代表性的6种简易算法48 Penman（48PM）法、Hargreaves-Samani（HS）法、Pristley-Taylor（PT）法、Irmark-Allen（IA）法、Makkink（MAK）法和Penman-Van Bavel（PVB）法的计算精度进行对比,结果表明：6种方法在四川省不同区域计算精度差异明显,HS法、PT法和PVB法较为精准,48PM法、IA法和MAK法误差较大,其中I区表现最好的为HS法,II、III和IV区表现最好的方法均为PT法;同时,除PT法和PVB法外,其余方法空间变异性较大（HS法在海拔较低的I、II区较为精准,在海拔较高的III和IV区结果远小于PM法,48PM法在四川东南地区的计算误差为11.1%~37.5%,在浅山丘区和高原区计算误差多大于50%）。因此,计算四川省的参考作物蒸散量时,推荐在东部盆地区使用HS法,盆周山地区、川西南地区与川西高原区使用PT法。

Reference crop evapotranspiration （ET0） is an important parameter for water cycle and water balance. Accurate estimation of ET0 becomes vital in water resource evaluation and agricultural water resource utilization. Numerous methods have been proposed for estimating ET0, among which the Penman-Monteith （P-M） model recommended by Food and Agriculture Organization of the United Nations （FAO） in 1998 is the best one to compute ET0 at present due to its foundation in physics and comprehensively considering the relationships. FAO has accepted the P-M model as the standard equation for the estimation of ET0 since it provides the highest accurate results across the world no matter in an arid or humid environment. But the main problems on computing ET0 by the P-M model are its complicated nonlinear process and requirements of many climatic variables. Thus, there is an urgent need to develop a much simpler and more appropriate model in the areas with limited data. This paper compares the accuracy of the Hargreaves-Samani （HS） method, Makkink method, Priestley-Taylor （PT） method, Irmark-Allen （IA） method, Penman-Van Bavel （PVB） method and 48PM method. To obtain the best calculation methods and assess its adaptability, the Sichuan Province is divided into 4 regions （including the eastern basin （I）, the moist mountainous area （II）, the southwest valley area （III） and the western plateau zone （IV））, and the daily ET0 in 46 stations from 1954 to 2013 is calculated. Then, this paper takes the ET0 calculated by the P-M model as a standard, and makes a comparison among the 6 methods. The results show that all methods are obviously variable in different regions. The HS method, the PT method and the PVB method are more accurate while the 48PM method, the IA method and the Makkink method have a larger error. Unfortunately, there is no method that performs good in all of 4 regions except the PT and PVB methods due to the different terrain or climate in different area. The HS method is relatively accurate in Area I and II which have a lower altitude; the 48PM method has a relative error more than 50% in the shallow hilly area and plateau area, while its relative error is lower in basin areas, such as -25%-11.1% in Batang and Dege, and 11.2%-37.5% in southeast area. Finally, we find that the best methods in the area of I and II are the HS method （root mean square error （RMSE） 0.58 mm/d, mean absolute error （MAE） 0.45 mm/d, mean relative error （MRE） 0.02） and the PVB method （RMSE 0.61 mm/d, MAE 0.39 mm/d, MRE -0.15）, and the best method in the area of III and IV is the PT method （RMSE 0.55-0.6 mm/d, MAE 0.44-0.45 mm/d, MRE 0.02-0.06）. Therefore, the HS method can be attained as the best one for calculating ET0 in the eastern basin, the PVB method can be the best one for the moist mountainous area, and the PT method can be similarly chosen in the southwest valley area and the western plateau zone in Sichuan.