Influência das oscilações climáticas tropicais na evolução da linha de costa atlântica do Pará-Brasil

Abstract

Understand how the shoreline (LC) position dynamically changes in response to meteoceanographic processes and climate variability is essential to predict and mitigate the impact of future extremes on the Atlantic Coast of Pará (CAP). This thesis aimed to provide the first quantitative assessment of the relative influence of the El Niño-Southern Oscillation (ENSO) and Atlantic Meridional Mode (AMM) climate indices on meteoceanographic processes (wave climate, winds and precipitation) and on beach morphodynamics along the coast. In this study, the significant wave height (Hs), mean wave period (Tz), speed (Wspd) and wind direction (Wdir) of the Era-Interim data (1979-2017) together with in situ wave data measurements on a macrotidal beach were used to define wave climate and its variability. Spectral analysis was used to quantify the wave propagation energy towards the LC. The results indicate that in CAP there are 3 modes of wave variability: 1) North-Northeast (N-NE) swell waves (frequency band – 0.04 – 0.14 Hz) during the rainy season; 2) Waves formed by the action of winds (windsea) from the Northeast (NE) (frequency band 0.14 – 0.33 Hz); and 3) East-Southeast (ESE) wind waves (frequency band 0.14 – 0.33 Hz) each with distinct wave power signatures. The behaviour of meteoceanographic processes associated with the main tropical climatic indices was analysed through the composites, whose results indicated more energetic waves, longer periods, greater precipitation and less intense winds during the La Niña and positive phases of the AMM. Less energetic waves, shorter periods, less precipitation and more intense winds were observed during the El Niño and negative phase of the AMM. In order to understand how the LC positions (obtained through a spectral approach by the Modified Water Index by Normalized Difference) in the CAP respond to climate variability and meteoceanographic processes, correlations were made between climate indices and change distances of LC. Cross-correlation values between climate indices and LC indicate that there is significant climate forcing, as they showed that the effects of ENSO and AMM were found in the Tropical Atlantic Ocean after 3-12 months. Therefore, changes in coastlines are associated with periodic variations in atmospheric forcing as climatic indices that modulate the position of the ITCZ, altering seasonal patterns in rainfall and wind regimes and their effects on sediment transport processes. Keywords: meteoceanography; climatic variability; beach morphodynamics.