Comparison of the Evapotranspiration Estimated by the Eddy CovarianceMethod and Semiempirical Methods in a Semiarid Zone

Abstract

This research studies the actual evaporation, measured with an Eddy Covariance station (EC), which, through micrometeorological methodologies obtains data that is necessary but difficult to measure for the calculation of evapotranspiration (ET). These types of stations are characterized by the fact that the investment in them is high and the placement must be planned carefully to carry out their activities. The real data of evapotrans piration from EC will be compared with other methods that estimate ET by correlation. The methods in turn are divided in two types by the way they calculate either potential ET (ETP) or reference ET (ET0). The theoretical-semi-empirical methods that handled ETP daily were Makkink, Hargreaves, Hamon, and the Turc method was used for monthly calculations. The FAO-56 Penman-Monteith method was used for daily calculations of the ET0; this work also includes the monthly ET downloaded from MODIS which is part of estimates through remote perception. The 1:1 correlation between EC and the semiempirical methods usually show a correlation R2=0.6, however, it is shown that the theorical and semiempirical methods underestimate the evapotranspiration and that their answer is not adequate for the semiarid zone, even when modulated for dry (runoff) and wet (flood) conditions for the data base, since the answer of the semiarid systems is very sensible to the availability of water for their essential development and balance.