Estimation of evapotranspiration from satellite data for the Alto Beni region, northern La Paz

Carlos Eduardo Choque Tarqui

Abstract

Evapotranspiration (ET) results from a simultaneous process of evaporation and transpiration. In a reference area, which occurs without water restrictions, it is called evapotranspiration of the reference crop (ETo). The Penman-Monteith FAO equation, proposed by Allen, Pereira, Raes and Smith (2006); Thornthwaite et al. (1944); Hargreaves et al. (1985); Blaney and Criddle (1950) and Turc (1961), was used for this study. The climatic information needed to estimate ETo is not sufficient because the local meteorological stations are very scarce and are no longer functioning, so data from the simulators recommended by FAO LocClim (2005) and NASA (power larc) were used. The Alto Beni region extends from 14º 56' 55'' to 15º 56' 14'' South and longitude 66º 48' 04'' to 67º 36' 42'' at an altitude of 300 to 1,800 m above sea level and covers an area of 4,836.62 km2. It is an important agricultural zone because it provides the city with a large part of its food products. The ETo results obtained in the spatial modeling show different values distributed in the region, which vary in each season of the year. It is asserted that, in most of the methods, the water deficit starts in the middle of April until September, and the highest peaks from October to March. The statistical analysis of the ETo results shows that the Thornthwaite model is the most accepted with an R² correlation coefficient of 0.966, followed by Blaney-Criddle with 0.969, and in last place the Hargreaves and Turc methods. The most accepted and applied model for the area is Thornthwaite, which has a very similar behavior to the PM-FAO, it does not overestimate the water demands and its calculations reflect the events of the region.