SENSITIVITY ANALYSIS AND REGIONALIZATION OF REFERENCE EVAPOTRANSPIRATION FOR THE AMAZON REGION.

Abstract

Sensitivity Analysis (SA) is important to understand the relative importance of climate variables in the reference evapotranspiration (ETo) computation. In this study, a sensitivity coefficient was used to predict ETo responses to disturbances of five climatic variables in the Amazonian Hydrographic Region - AHR (Brazilian Amazon). The ETo was estimated using the standardized equation of Penman-Monteith-FAO (PM-FAO). A 15-year meteorological data set of 38 surface meteorological stations were used in the study. An additional analysis was also presented to determine homogeneous regions of ETo by means of Cluster Analysis. The results showed that seven homogeneous sub-regions are sufficient to divide the AHR into different ETo patterns which were separated considering the intensity and the seasonal pattern of ETo. By the SA, the variables that contribute most to the computation of ETo using the PM-FAO method were the balance of radiation (Rn) and wind speed (u2). These results demonstrate that, in general, it should be emphasized to precise measures of insolation, since the precise estimation of Rn is directly associated with the measurement of this variable as well as of u2, which proved to be the second most influential variable in the ETo computation.