FLOODING EPISODES IN THE SEMI-ARID REGION OF THE S O FRANCISCO RIVER BASIN IN

This work aims to determine the dominant scales, the relative contribution of the atmospheric variables and the physical processes involved in intense rainfall and flooding episodes that gave rise to inundations in the Submédio San Francisco in April 1985, with emphasis to the period of 9th to the 12th of this month, called here of critical period. Surface and altitude observational data of the Petrolina-PE area and reanalysis data were analyzed using the factorial analysis by means of principal components (EOF). The results show that a model that a three-component is adequate to represent the structure of the variables at the local scale, retaining 74% of the total variance and existence two groups of dominating physical processes on this scale: the first, involving the atmospheric moisture content and instability, and the second, the radiative heating of the surface. For the data set of reanálise a model with four components is adequate, retaining 75% of the total variance. The most significant scores indicate that conditions on the synoptic scale were determinant through a high moisture content in the lower troposphere and mass convergence (divergence) in the lower (higher) troposphere. The application of the ACP to the data of reanálise of the level of 925 hPa indicates that the first factor, related with the sinotic scale, and as, with sub-sinóticas scales, have significant scores with the variables, except of the 12th day for air temperature, when the third factor dominates, possibly a heating in to heating on the mesoscale caused by convective processes.