VARIABILIDADE ESPAÇO TEMPORAL DA EVAPOTRANSPIRAÇÃO POTENCIAL NO SUBMÉDIO DO RIO SÃO FRANSCISCO UTILIZANDO A ANÁLISE FATORIAL EM COMPONENTES PRINCIPAIS

Abstract

Evapotranspiration is one of the most important processes of the hydrological cycle, consisting of the link between energy, climate and water availability. Therefore the aim of this work was to apply multivariate statistics, factor analysis by principal components (PCA) in monthly series of potential evapotranspiration (ETP) in the Lower Basin of the Valley of the Sao Francisco region. We chose this region because it is embedded in the Brazilian semiarid region, which is one of the areas of the country more susceptible to the effects of climate change, both in the physical aspect as socioeconomic. The data used are time series (1960-1990) average air temperature (Tmed) expanding in grids with a resolution of 0.5 ° x 0.5 ° derived from the Regional Climates for Impacts Studies Providing ( PRECIS ) the Hadley Centre model. To determine the ETP was chosen the method of Thornthwaite and Mather (1955). Factor analysis was applied to the spatio-temporal mode for ETP data using SPSS software. The average value of 1.386 mm was observed for annual series of ETP in the study area. For the study period of 1960-1990 the set of analyzed data can be represented by three factors together explain 96.7 % of the variability of the data studied. The addition of ( 3.3% ) are associated with noise. The explanation of the first factor is directly influenced by variables related to water availability and energetic. The second factor can is associated with incidence of rainfall producing systems, such as Tropospheric Cyclonic Vortex and the ITCZ, and the influence of land use - irrigated crops . Finally the third and last factor has a direct relation to the change of dry to wet, and possibly soil type of the region.