Forçantes meteoceanográficas e desastres costeiros no Litoral Oriental do Rio Grande do Norte, Nordeste Brasileiro

Abstract

Intense unplanned urbanization in coastal zones brings risks and environmental disasters through the interaction of meteorological and oceanographic factors, in addition to human activities, which impacts vulnerable populations and ecosystems. The coast of Rio Grande do Norte State (RN), Northeast Brazil, has experienced successive flood and erosion events that cause damage to infrastructure, traditional populations and sensible ecosystems such as estuaries, mangroves and sandbanks. The study area is the Eastern Coast of RN, mainly the urban beaches Ponta Negra-Via Costeira, city of Natal, and Barra de Maxaranguape, city of Maxaranguape. This study aims assess environmental drivers related to extreme events, disasters and public calamities in urban beaches of the area. It were obtained both observed and hindcasted wind, precipitation tide and wave time series, from meteorological gauges of the Brazilian National Institute of Meteorology, Agricultural Research Company of Rio Grande do Norte, AVISO satellite altimetry and global hindcasts (ERA5 and Wavewatch III), from 1979 to 2021. Generalized Pareto Distribution (GPD) fittings of wave significant high (Hs) and precipitation were performed. Registers of disasters along the coast of study area were collected from online local media. Offshore waves were propagated shoreward on Barra de Maxaranguape through SMC-Brasil model. Wave average energy flux (EF) was estimated at closure depth along Ponta Negra and Via Costeira beaches (PN-VC) with SMC-Brasil. On the Eastern RN continental shelf, waves have reached Hs maximum of 3.30 m, average of 0.76 m, coming from east-southeast and southeast. Winter and spring seasons have presented higher waves, related to action of trade winds. GPD estimated Hs increasing till 2.7 times over its average each 10 years. Increasing of wind speed is more important than its scalar value, to form an extreme wave. Hs at the virtual station had its upper peak either at the same day or one-two days before of coastal damage, which indicates that offshore ocean storms can quickly propagate coastward. On Barra de Maxaranguape, each 10 years, it is likely to happen a precipitation event of 138,71 mm at least once. Talus deposits laid on the beach face reduce incident wave energy. The Ponta Gorda headland receives the highest waves, thus, these are the most energetic sea states. In the urbanized stretch of Barra de Maxaranguape beach, average wave energy flux reaches 2.08 x 104 J/ms with an increasing trend since the 70’s. PPN-VC incident EF are between 8.55*103 and 20.54*103 J/ms, decreasing in Morro do Careca’s bay and stronger in Via Costeira, coming from east and east-southeast, causing damages to waterfront urban facilities. Variations of EF in the 70’s and 2000’ decades are associated to erosional tipping points in PN. The several disasters that had happened on PN-VC are likely to repeat on Barra de Maxaranguape, serving as a decision-making reference for the entire Eastern Coast of Rio Grande do Norte.