Estimativa da evapotranspiração de referência em Campina Grande-PB.

Abstract

The objective of the present study was to estimate the evapotranspiration of daily reference for the city of Campina Grande-PB (EToT) using an empiric formula, based on the daily thermal amplitude. It was also evaluated the evapotranspiration of daily reference using the empiric methods of Penman-Monteith (EToPM), Hargreaves (EToH) and Linacre (EToL), and, in a future time, their correlation with EToT by season. For each season it was also analyzed the variation of precipitation, temperature, rela tive humidity of the air and the solar irradiation during the year of 2004 in Campina Grande-PB. For that purpose, daily values of temperature, relative humidity of the air, solar irradiation, precipitation, pressure and speed of the wind were collected at 2m of the Automatic Meteorological Station model CR23X, installed in the Universidade Federal de Campina Grande (UFCG), in the period of January 01 to December 31, 2004. Such values were registered in the interval of 10 minutes. By proceding that way, it was verified that the correlations between EToT and EToH had better adjustment, whose the coefficients were: R² = 0,7882 (for the year), R² = 0,9796 (for the summer), R² = 0,8253 (for the autumn), R² = 0,878 (for the winter) and R² = 0,914 (for the spring). It was detected that EToPM and EToL methods were not well adjusted for Campina Grande-PB for the four seasons of the year of 2004. That finding evidence that EToT can be used in the form proposed to estimate the reference evapotranspiration in Campina Grande, considering that Hargreaves’ method is one of the principal methods of estimate described in the literature. Among the proposed equations, the only restriction found was EToT for the summer, once it was not well correlated with the daily thermal amplitude, presenting a result of R² lower than 0,80. In this situation, the use of the annual equation is recommended.