TREND ANALYSIS OF THE REFERENCE EVAPOTRANSPIRATION FOR THE SOUTHWESTERN AMAZON, BRAZIL.

The changes in climatic conditions can affect demand of water in regions because the evapotranspiration is affected by changes weather elements. The goal of this study was to identify possible trends in the reference evapotranspiration (ETo) to Acre State, with study units to Rio Branco locations (Acre’s capital), Tarauaca and Cruzeiro do Sul considering a period of 30 years, using monthly meteorological stations data. The methodology was adopted to achieve meteorological consistency data, in this way was made the gap filling in the time series by means of multivariate techniques. The trend analysis was performed using the Mann-Kendall nonparametric and your magnitude through the Theil-Sen test. The indirect method of Penmann-Montheith was used to calculate the ETo. It was found that there is upward trend in ETo at the autumn, winter and spring seasons and that became a significant through the years 1990, 1996 and 2001 to cities of Cruzeiro do Sul Tarauaca and Rio Branco, respectively. The average temperature datasets, minimum temperature, solar radiation and global solar radiation showed upward trend at 5% significance for all that three locations. These being the main responsible for the increase in ETo in these locations.