ABSTRACT
The most
precise equation in order to estimate the evapotranspiration (ET) of crops is
the Penman-Monteith (PM). However, the PM equation needs specific data that, in
the majority of Mexico’s irrigation districts, it is not available because
there are few automated weather stations. For this reason, it is convenient to
develop simple methods that allow to precise estimation of ET. A reliable way
to estimate ET is by using the pan evaporation that, according to the revised
literature, continues to be used nowadays. Investigators like to include its
use in irrigation water management projects in various parts of the world.
However, this method uses Kp from the FAO that is not calibrated in Mexico. The
use of FAO Kp affects the precision of the results, since some variables like
radiation, wind, temperature and relative humidity vary from place to place;
therefore ET is under estimated or overestimated. This paper presents an
original contribution across method to estimate “Kp pan evaporation and ETo
monthly maps”, using information from 60 weather observatories included in The
Climate Normals (1941-1970) from Mexico, based on the PM method and the class A
pan evaporation. Once the Kp values were obtained from each weather
observatory, the Kringing method was used. This way, by interpolating data of
the triad “latitude, longitude and Kp” and “latitude, longitude and ET”,
monthly normalized maps of Kp and ET were established for Mexico, except the
upland areas (Sierra Madre Occidental and Sierra Madre Oriental), as well as
other highland zones above 2700 meters over sea level, for the highest
observatory is located in Toluca, State of Mexico (key 14-0039), at 2680 m over
sea level.