Historical assessment of extreme coastal sea state conditions in southern Brazil and their relation to erosion episodes

Abstract

Intense cyclonic weather systems in southern Brazil generate ocean storms which can, in a temporal scale varying from few hours to a day completely erode a beach profile from its maximum accretion state. Mid-latitude cyclogenesis with low pressure centers in the deep ocean and along the coast increases the intensity of the Mid-Atlantic storms causing storm surges and storm waves. Preliminary results from a hindcast of wave energy at deep water (100 m), performed with a wave model using winds from reanalysis ( period 1979 - 2008), indicated a total of 40 extreme events (wave height above 6 m). These events cause maximum erosion and surge elevation on the order of 62.96m³/m and 1.827 m respectively. Four patterns of synoptic situations capable of generating extreme events were identified. Among the 40 events, 53.66% had the trajectory of Pattern II and 26.82% were associated to Pattern III, representing both 80% of the total. Coastal erosion episodes where mostly associated with Pattern II, while Pattern III caused the highest surges. In a climate change scenario this study shows no important differences in the amount of the extreme events along the last thirty years.