基于析因数值实验方法的蒸发皿蒸发归因研究

A new method to attribute changes of pan evaporation:The experimental detrending approach

蒸发皿蒸发是唯一可长时间大范围观测的潜在蒸发,其准确估算和长时间序列趋势变化归因分析,对变化环境下干旱研究、水文过程理解分析与预估具有重要意义。本文筛选出416个具有连续观测的气象台站资料,率定了PenPan模型中适合模拟中国20 cm口径(D20)蒸发皿蒸发的风速函数,发展了基于去趋势法的析因数值实验归因法,对比了此方法与常用的偏导归因法在1960-2014年、1960-1993年("蒸发悖论"时段)及1993-2014年("蒸发悖论"消失)蒸发皿蒸发趋势变化的归因结果。结果表明,使用新率定的风速函数f_q(u_2)=3.977×10^(-8)(1+0.505u_2)能更准确模拟中国D20蒸发皿蒸发;相较于偏导归因法结果,析因数值实验法也能对蒸发皿蒸发趋势变化进行定量归因分析,且归因结果略优于偏导归因法结果;此外,可利用析因数值实验法的基准态信息来对偏导归因法结果进行校正,从而更准确地对蒸发皿蒸发趋势变化进行归因分析,加深对蒸发皿蒸发趋势变化的理解,为水文水循环研究准确分析提供保障。

Pan evaporation is the only long-term observation of potential evaporation around the world. In analyzing and predicting how droughts and hydrological cycles might change in a warming climate, change of pan evaporation is one crucial element to be understood. In this paper, we chose 416 sites with continuous monthly observations over 1960-2014 in China. We calibrated the wind function in the PenPan model to improve the estimation of pan evaporation.We developed a new approach, i.e., the experimental detrending（ED） approach, and made comparison with the traditional partial differential（PD） method in attributing changes of pan evaporation for the periods of 1960-2014, 1960-1993（evaporation paradox） and 1993-2014（evaporation paradox disappeared）. The results first showed that improvement in estimating pan evaporation can be made when using the new calibrated wind function： fq（u2）=3.977×10-8（1＋0.505 u2）. The comparison then showed that both methods can well attribute changes of pan evaporation, and the ED approach performs slightly better than the traditional PD method. In addition, the ED approach can help make effective adjustment for the PD method in attribution analysis so as to better understand the change of pan evaporation. Hence, the ED approach is recommended to assist a better understanding and prediction of water-energy cycles in a changing climate.