Evaluation of Potential Evapotranspiration Based on CMADS Reanalysis Dataset over China

Yue-Ping Xu,Xichao Gao,Kejun Zhang,Jie Wang,Ye Tian

doi:10.3390/w10091126

Abstract

Potential evapotranspiration (PET) is used in many hydrological models to estimate actual evapotranspiration. The calculation of PET by the Food and Agriculture Organization of the United Nations (FAO) Penman–Monteith method requires data for several meteorological variables that are often unavailable in remote areas. The China Meteorological Assimilation Driving Datasets for the SWAT model (CMADS) reanalysis datasets provide an alternative to the use of observed data. This study evaluates the use of CMADS reanalysis datasets in estimating PET across China by the Penman–Monteith equation. PET estimates from CMADS data (PET_cma) during the period 2008–2016 were compared with those from observed data (PET_obs) from 836 weather stations in China. Results show that despite PET_cma overestimating average annual PET and average seasonal in some areas (in comparison to PET_obs), PET_cma well matches PET_obs overall. Overestimation of average annual PET occurs mainly for western inland China. There are more meteorological stations in southeastern China for which PET_cma is a large overestimate, with percentage bias ranging from 15% to 25% for spring but a larger overestimate in the south and underestimate in the north for the winter. Wind speed and solar radiation are the climate variables that contribute most to the error in PET_cma. Wind speed causes PET to be underestimated with percentage bias in the range −15% to −5% for central and western China whereas solar radiation causes PET to be overestimated with percentage bias in the range 15% to 30%. The underestimation of PET due to wind speed is offset by the overestimation due to solar radiation, resulting in a lower overestimation overall.

Highlights

Evapotranspiration (ET) is a fundamental component of the hydrological cycle and a route for energy transfer between the earth’s surface and the atmosphere
To −5% for central and western China whereas solar radiation causes Potential evapotranspiration (PET) to be overestimated with percentage bias in the range 15% to 30%
This study evaluated the use of CMADS datasets in estimating PET across China during This study evaluated the use of CMADS datasets in estimating PET across China during the the period 2008–2016

Summary

Introduction

Evapotranspiration (ET) is a fundamental component of the hydrological cycle and a route for energy transfer between the earth’s surface and the atmosphere. It is important in activities such as evaluating water resources [1], drought forecasting [2], and managing irrigation [3]. Actual evapotranspiration is usually measured indirectly by eddy covariance (EC) [5], the Bowen ratio method [6], lysimetry [7], and scintillometry [8]; ET cannot be observed at a large scale by these techniques. Eddy towers and the Bowen ratio method observe over only hundreds of meters, depending on wind speed, tower height, and canopy level.

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