不同互补模型对青藏高原多年冻土区地表实际蒸散发的模拟能力评估

Evaluation of Complementary Relationship Model on Land Surface Actual Evapotranspiration in the Permafrost Region of Qinghai-Xizang Plateau

蒸散发是地气水热交换的重要环节,其变化对水资源管理和生态环境具有重要的影响。气候变暖背景下,青藏高原多年冻土不断退化,多年冻土区近地表水热条件发生改变,进而影响着该区域的蒸散发过程。本文利用位于青藏高原多年冻土区腹地的唐古拉综合观测场2010年1月1日至2011年12月31日的气象和涡动等实测资料,选择基于互补蒸散原理的四种半经验模型,评估了不同模型率定参数前后模拟日实际蒸散发的能力,分析了不同模型中参数的敏感性。结果表明,模拟的实际蒸散发量对模型中参数α的取值非常敏感,不合理的参数取值会对模拟精度产生重要影响。使用默认参数值会导致日蒸散发量模拟值明显偏高,其中,S2017模型模拟精度最高,均方根误差值为0.44 mm·d^(-1);率定参数后各模型整体上均能较好地模拟出日实际蒸散发量及其变化特征,均方根误差值在0.3~0.4 mm·d^(-1),各模型中模拟精度最高的为C2016模型,其次分别为H2018模型、B2015模型和S2017模型,相较而言,H2018模型在率定前后模拟结果更为稳定,显示出该模型对参数的依赖性最低;另外,年内不同时期的模拟精度存在明显差异,完全融化期的模拟结果相较完全冻结期和日冻融循环期与实测值更接近,相对偏差均值分别为6.0%,82.3%和43.4%。本文旨在探讨不同互补蒸散模型在青藏高原多年冻土区地表实际蒸散发模拟的适用性,结果可以为该区域长时间序列蒸散发估算提供一定的参考依据。

Evapotranspiration is an important link to water and heat exchange between soil and atmosphere,and its changes have an important impact on water resources management and ecological environment.In the context of global warming,the permafrost on the Qinghai-Xizang Plateau is continuously degraded,and the near-surface hydrothermal conditions in the permafrost regions have changed,which further affect the evapotranspiration process.In this paper,four semi-empirical models based on the complementary principle of evapotranspiration are selected to evaluate the ability of different models to simulate the actual evapotranspiration on a daily scale before and after calibrating parameters,and also analyze the sensitivity of the model parameters,which using the meteorological and eddy covariance measurements from January 1,2010 to December 31,2011 at the Tanggula comprehensive observation site located in the hinterland of the permafrost region of the Qinghai-Xizang Plateau.The results show that the simulated actual evapotranspiration is very sensitive to the value of parameterαin the models,unreasonable parameter values led to poor simulation ability.Specifically,the use of default parameter values will lead to marked higher simulated values of daily evapotranspiration,the S2017 model has the highest simulation accuracy with RMSE value of 0.44 mm·d^(-1).After parameters calibration,all models can simulate variation characteristics of daily actual evapotranspiration,RMSE values are between 0.3 and 0.4 mm·d^(-1),the model with the highest simulation accuracy is the C2016 model,followed by H2018 model,B2015 model and S2017 model,in comparison,evapotranspiration simulated by H2018 model exhibits more stable results,which indicates lower parameter dependency.In addition,accuracy of simulation exists significant difference during various period within the year,and the simulation results of the thawed period are closer to the measured values than those of the frozen period and the daily freeze-thaw cycle period,mean relative deviation values are 6.0%,82.3%,43.4%,respectively.The purpose of this paper is to explore the applicability of different complementary evapotranspiration models to the simulation of actual surface evapotranspiration in the permafrost region of the Qinghai-Tibet Plateau,and to some extent,the results can provide reference basis for the estimation of long time series evapotranspiration in this region.