Introduction:

Estimating evapotranspiration of cultivated areas is commonly based on the calculation of reference evapotranspiration (ETo), and is essential in climatic and hydrological studies, as well as in projects related to water management in agriculture.

Objectives:

To evaluate ETo and analyze its behavior during the rainy season on a daily, monthly and seasonal basis.

Methodology:

Daily data series on temperature, radiation, atmospheric pressure, relative humidity and wind speed from five weather stations in the Lerma-Chapala basin were used. The ETo calculation was based on the application of the Penman-Monteith method.

Results:

ETo during the rainy season followed a decreasing pattern, characterized by being non-linear. At the beginning of the season, values higher than 6 mm·day-1 were observed, and at the end they were lower than 2 mm·day-1. Correlation analysis showed that ETo depends on relative humidity and radiation.

Study limitations:

The number of stations used was very low for the size of the basin because the network of automatic weather stations is still under development.

Originality:

There are very few studies focused on evapotranspiration variation as a function of elevation and meteorological variables, in addition to a specific analysis in the rainy season.

Conclusions:

The seasonal behavior of ETo shows important changes related to the behavior of relative humidity and radiation, which can have a significant impact on crop water needs.

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