Variabilidade da precipitação pluviométrica na bacia hidrográfica do Alto Jacuí- RS

Abstract

The rain precipitation is one of the climate elements with wider impact on the geographical space, because it is related with several sectors of the society. Therefore, the general purpose of this work is to analyse the spatio-temporal variability of the rain precipitation of the water shedad of the Alto Jacuí river – RS between the years 1980 and 2010. The study area is located at the Hydrographical Region of Guaíba, covers an area of 12,985.44 km ². Monthly and yearly data were used for the analysis, available from Companhia Estadual de Energia Elétrica Geração e Transmissão (CEEE-GT), Agência Nacional das Águas (ANA) and Fundação Estadual de Pesquisa Agropecuária (Fepagro). Statistical parameters as average, standard deviation and coefficient of variation will be used in order to analyse the variability of rain precipitation at the water shedad. The standard years were statistically classified through the standard deviation of the average rain precipitation between all years. The spatialization of the rainfall data was done through spatio-temporal panel and isohyetal maps of the total average precipitations of all rainfall points on monthly, seasonal and yearly scale, as well as the data related to the seasonal and annual periods of the standard years. As a result, it can be observed that October has the highest historical monthly average and March the lowest historical average for the basin. Related to the historical seasonal average of the Alto Jacuí basin, it is observed that the spring has the highest seasonal average. On the standard year classification, the years 1991, 1992 and 2002 were selected as the less rainy, habitual and rainier, respectively. When analysing the total yearly average rain precipitation distribution in the basin, it can be perceived that the lower rates are concentrated on the south portion. The north and southwest present the highest rates of yearly average. Thus, it can be inferred that the distribution of the total average rainfall follows the cold fronts shift along with the altitude effect which influence the rainfall distribution because the east portion of the basin presents the higher altitudes. During the seasonal period also occurred vast variability of rainfall distribution, being spring the rainier period of the basin. The central portion of the basin presented the lower averages during seasonal periods. During spring and autumn the north portion achieved the higher rainfall averages. In contrast, during the winter the east and southwest portion presented the higher averages. It can be perceived that the geographical localization of the basin presents a vast hypsometric variation of approximately 690 meters throughout its extension, resulting on a considerable variation of the rainfall distribution due to the orography of the water shedad of the upper Jacuí. Hence, it is understandable to consider that the orographic effect has a considerable influence on the climate issue and is an important factor on the rainfall variation.