Estimation of monthly evaporation in a class-A pan in the Mexican Republic through temperature data

Abstract

Based on the meteorological stations of the Mexican Republic that have monthly evaporation records (E) in class-A pans, an empirical formula of the type was calculated through a non-restricted numerical optimization, where RE is the extraterrestrial solar radiation, DEV is the vapor deficit and Co is a correction term obtained by a validation procedure. The proposed equation has a mean standard error of mm/month. Later, a relation between monthly temperatures of dew point and minimal temperature was searched in order to avoid the use of relative humidity records, since they are very scarce; there are only in the whole country. With this new approach, other corrections were deduced. The proposed empirical formula has an acceptable forecasting estimation in places with an altitude greater than m.a.s.l., according to the test ran in weather stations in the country. However, it is not recommended in coastal regions where observed evaporation is generally overestimated. An empirical formula for the estimation of annual mean evaporation in class-A pans is also proposed, using just the location latitude and the respective values of minimal and mean temperatures. This latter equation gives similar results than those of the monthly estimation formula previously derived.