Effects of evapotranspiration on the water balance of the Valley of Mexico

Abstract

The total recharge area of the Valley of Mexico is 9587 kJn2. Climatological data from 82 weather stations were used to calculate annual precipitation values for single subbasins. The total precipitation volume in the Valley of Mexico from 1980 to 1985 was 226 m3/s. Various empirical and semi -empirical equations resulted in underestimations of the actual evapotranspiration ET actual by 15 to 20% for the Turc-method, whereas the equations of Morton yielded too high values. The methods of Blassey-Morin, Coutagne and Budyko are the most reliable ones, yielding an average percentage of 80% of the total yearly precipitation. Volcanic mountain ranges, such as the Sierra Chichinautzin lose 50% to 65% by evapotranspiration, whereas their foothills and the northern plains between Sierra Guadalupe and Pachuca range between 85% and 95%. The largest infiltration is expected at mountain ranges, especially peak regions of the Sierra Las Cruces, Sierra Chichinautzin and Sierra Nevada. The formulas include various climatological factors such as the amount of rainfall, temperature, duration of insolation, latitude, or relative humidity but the composition of the subsoil and its geotechnical parameters were not considered.