Evaluating eddy covariance method by large-scale weighing lysimeter in a maize field of northwest China

Accurate determination of evapotranspiration (ET) is useful to develop precise irrigation scheduling Although eddy covariance (EC) is a direct method which is widely used to measure ET its performance in and region of northwest China is not clear In this study ET measured by EC (ETEC) was compared with that by large-scale weighing lysimeter (ETL) during the whole growing season of maize in 2009 Energy balance ratio was 084 for daytime fluxes indicating that lack of energy balance closure occurred so daytime ETEC was adjusted by Bowen-ratio forced closure method Compared to the corresponding ETL half-hourly daytime ETEC was underestimated by 21 8% without the adjustment and 4 8% with the adjustment Furthermore nighttime ETEC was adjusted using filtering/interpolation method Mean error between half-hourly nighttime ETEC and ET, decreased from 30 2% without the adjustment to 10 3% with the adjustment After such adjustment of day and night measurements daily ETEC was underestimated by 6 2% compared to ETL These results indicated that the adjusted ETEC well matched with the ETL Moreover the discrepancy of adjusted total ETEC and ETL was decreased to 3 2% after subtracting the overestimated ET by lysimeter resulting from irrigation and heavy rainfall events Thus after appropriate adjustments of observations eddy covariance method is accurate in estimating maize ET in the and region of northwest China (c) 2010 Elsevier BV All rights reserved