Variabilidade das características da precipitação e temperatura ao longo do leste da Bacia Amazônica

Abstract

Past work on the precipitation and temperature climatologies of the Amazon Basin did not give much emphasis on the spatial variability and local variabilities. Graphical examination of the progressions of monthly and daily precipitation observations for the last 52 years in the eastern Amazon Basin shows that both the spatial variability and the temporal variability of precipitation at many places are appreciable. As the precipitation in the basin is of small scale nature in time and in horizontal extent, the numerical climate prediction models cannot satisfactorily capture such variability. The best way to provide guidance for the forecasters of the region is to establish the spatial and temporal variabilities of precipitation and temperature based on observational datasets. Another important aspect to examine is the long period trends (or changes) in the local climatologies along the eastern Amazon Basin. The need to study this aspect arises due to global warming and rapid regional anthropic forcings such as deforestation, agriculture and forest fires. The present study addresses these two aspects with the help of observational datasets. The daily rainfalls at each of the eight stations from Manaus to Belem are categorized into Light, Moderate, Intense and Very Intense rains and No-Rain days. The frequencies in each category at the eight stations are obtained. Extreme rainfall events are identified. Main results of the investigation are: (i) Annual precipitation reduces to the east from Itacoatiara to Monte Alegre and increases further east up to Belem. (ii) The annual rainfalls at the stations, especially the extremes, do not show clear-cut influence of the ENSO phenomenon. (iii) The three-month most-rainy and least-rainy periods vary only slightly along the basin. (iv) Belem presents smallest frequencies of No-Rain days as well as Very Intense-Rain Days. (v) Due to similarities in seasonalities, the correlations between the series of observed precipitation at different stations are high and positive. The filtered series, after removing the annual cycle, present smaller correlations, but are significant. (vi) The monthly average temperature series show positive trends when analyzed over a 52-year period in all locations. Additionally, in the three most recent decades, there is a significant increase of around 1°C, except in Monte Alegre, where there was no significant trend during the same period. (vii) The precipitation series at Belem showed significant positive trend, attributable to urbanization and deforestation effects. We consider that the results obtained are helpful to meteorologists of the region.