Comparison of Ten Potential Evapotranspiration Models and Their Attribution Analyses for Ten Chinese Drainage Basins

Abstract

Potential evapotranspiration (E_PET) is usually calculated by empirical methods from surface meteorological variables, such as temperature, radiation and wind speed. The in-situ measured pan evaporation (ET_pan) can also be used as a proxy for E_PET. In this study, E_PET values computed from ten models are compared with observed ET_pan data in ten Chinese river basins for the period 1961–2013. The daily observed meteorological variables at 2267 stations are used as the input to those models, and a ranking scheme is applied to rank the statistical quantities (ratio of standard deviations, correlation coefficient, and ratio of trends) between ET_pan and modeled E_PET in different river basins. There are large deviations between the modeled E_PET and the ET_pan in both the magnitude and the annual trend at most stations. In eight of the basins (except for Southeast and Southwest China), ET_pan shows decreasing trends with magnitudes ranging between −0.01 mm d⁻¹ yr⁻¹ and -0.03 mm d⁻¹ yr⁻¹, while the decreasing trends in modeled E_PET are less than −0.01 mm d⁻¹ yr⁻¹. Inter comparisons among different models in different river basins suggest that PET_Ham1 is the best model in the Pearl River basin, PET_Ham2 outperforms other models in the Huaihe River, Yangtze River and Yellow River basins, and PET_FAO is the best model for the remaining basins. Sensitivity analyses reveal that wind speed and sunshine duration are two important factors for decreasing E_PET in most basins except in Southeast and Southwest China. The increasing E_PET trend in Southeast China is mainly attributed to the reduced relative humidity.

摘 要

潜在蒸散 (E_PET) 通常是利用近地表的气象变量 (如温度、 辐射、 风速等) 借助经验公式计算得出, 站点观测的蒸发皿蒸发量 ( ET_pan) 也常被当作 E_PET 的替代品. 在本文中, 我们基于 2267 个站点的日观测气象数据, 将十组潜在蒸散模型计算得到的 E_PET与 1961–2013 年间中国十大流域的站点观测 ET_pan 进行对比分析. 紧接着我们利用一种统计评分方法, 对各流域中的 ET_pan 和模拟的 E_PET 之间的三组统计量 (标准差比值, 相关系数, 趋势比值) 进行了排序评分, 以此来筛选每个流域表现最好的模型. 计算得到的 E_PET 和 ET_pan 在量级和年际趋势上都有着很大的差异, 除了东南地区和西南地区以外的八个流域中, ET_pan的下降趋势都在-0.01mm d^-1 yr^-1 到 -0.03mm d^-1 yr^-1之间, 而E_PET 的下降趋势则总是小于-0.01 mm d^-1 yr^-1. 在各流域对不同模型进行对比分析后, 我们得到了每个流域表现性最好的模型. 其中, PET_Ham1 是珠江流域最适用的模型; 在淮河、 长江以及黄河流域, PET_Ham2 要优于其他模型; 在其它流域中, 则是以PET_FAO表现最好. 敏感性分析表明, 除了东南地区和西南地区以外, 风速和日照时数是影响 E_PET减小的最重要的因子, 而 E_PET 在东南地区的上升趋势则主要归因于相对湿度的减小.