Relação entre tipos de tempo, eventos de precipitação extrema e inundações no espaço urbano de São Sepé-RS

Abstract

Among natural elements the climate assumes importance in that it relates to the ambient question of the cities. The choice for the channel of the Meteoric Impact, among the subsystems of Sistema Clima Urbano (SCU System Urban Climate), justified for the constant episodes of floods in the urban area of São Sepé. In this context, the work has as objective to relate the extreme pluvial precipitation events with the occurrence of floods in the urban zone of São Sepé - RS, in the period of 1980 - 2006. To analyze the time-space distribution of the precipitation in the urban area, as well as its seasonal variation, it was opted to the installation of four rain gauges, made by craftwork form. The collection of the data of the rain gauge was carried through in the period of one year choosing the most representative month of each station of the year as sample: spring - October of 2005; summer - January of 2005; autumn - April of 2006; winter - July of 2006. Through the crossing of the extreme pluvial events founded in the analysis of the meteorological data with the episodes of floods notified in the local press, seven episodes of bigger impact in the urban space had been selected: Episode 1 - 05 the 07/05/1984; Episode 2 - 21/05/1984; Episode 3 - 16/12/1994; Episode 4 - 27 and 28/12/1997; Episode 5 - 03/10/2002; Episode 6 - 19/02/2003; Episode 7 - 10 and 11/09/2005. On the basis of the analysis of the episodes was observed that the minimum volume of precipitation capable to originate this type of impact is of 38 mm registered in 24 hours and the maximum volume of precipitation registered in 24 hours was of 121,8 mm. About the intensity of the precipitation it is verified that floods just occur when the precipitations are moderate to heavy or superior intensity (strong and very strong). The moderate precipitations are susceptible to cause floods only when followed by smaller intensities. Floods had been distributed in three groups about genesis of the episode that gave origin to them: floods related to the fast frontals crossing, the stationary fronts and the combined performance of tropical uncertainties and polar fronts. About the repercussions of floods in the urban space, in all analyzed episodes had occurred damages, such as invasion of the houses for waters and residents homeless, beyond material damages as the total or partial loss of the property and bridges and the damaged of the urban ways. Finally, it tried to mark the limits of the susceptible areas of floods, as well as those who can be reached as that the urbanization intensify. The susceptible areas of floods are situated at the edges of the Lajeado do Moinho and the river São Sepé. The definition and characterization of intense pluvial episodes, about the genesis, intensity and volume of rain, even thought of preliminary form, could be able to serve of base for prevention of these impacts, as well as posterior studies, being able to contribute directly for the urban planning of the city towards to assist the organization and rational use of the urban space.