Climate teleconnections and indicators of coastal systems response

Abstract

This article surveys secular urban sandy beaches erosion-accretion and its relationship with climate teleconnections, e.g., El Niño Southern Oscillation (ENSO), Atlantic Multidecadal Oscillation (AMO), and extreme events, e.g., storm surges, great rivers' floods, and heavy rains in adjacent basins. The paper aims to discuss these issues and the expected coastal retreat as a consequence of manmade climate changes, e.g., sea level rise (SLR) and increased storminess in the coming decades. Several beaches (Buceo, Malvín, Pocitos, Ramírez) and two tidal creek mouths (Carrasco and Pando), with different characteristics but all constrained by coastal linear infrastructure and two tidal creek sandy mouths were studied. These sites are located along the urbanised coast of the middle region of Río de la Plata microtidal river estuary. All of them show a more or less strong retreat trend with alternated fluctuations, e.g., weak retreat likely due to sea level rise, significant erosion very likely due to storm surges, and processes of loss of sediment stock, as well as episodes of sand recovery. Therefore, these beaches require interventions to preserve their beach prism and dry sand surface. In search for answers to better understand why and under what conditions the process of advance and retreat of the coastline occur, we have analysed different teleconnections and carried out reanalyses for wind anomalies during ENSO events from 1951-2010. Both weak and moderate erosion-accretion periods are likely related to atmospheric anomalies, e.g., wind direction changes and the consequent swell and littoral drift changes, related to El Niño and La Niña events. The former associated with accretion and the latter with erosion. In the past most interventions have been reactive. Increased knowledge of climate and weather relationship with the sedimentary balance provides an approach that would allow developing beach risk-management, pro-active strategies and climate adaption measures focused on the generation and recovery planning based on the analysis of the occurrence and prediction of El Niño / La Niña events.

Relationships Between the Sand Cycle and the Behaviour of Small River Mouths: A Neglected Process / O Ciclo Da Areia E O Comportamento De Estuários De Rios Pequenos: Um Processo Negligenciado

“…However, Verocai et al (2015) found a slight increase in the occurrence of events greater than 1.89 m AMSL, capable of modifying the coastal morphology, over the last decade. At the same time, a fluctuating trend in atmospheric energy has been observed, verified by storm surges with maximums at the beginning of the 20 th century and minimums between 1960 and 1970, and an increasing trend of the average energy since then, assimilable to the AMO variability (Gutiérrez et al, 2016). Higher intensity and frequency of storm surges and SLR would determine a highly erosive scenario for the coast of Montevideo (Orlando et al, 2019).…”

“…These beaches show a behaviour that responds to interannual ENSO-related variability, in particular, recovery (progradation and increase in sand volume) during El Niño events, and erosion related to the occurrence of strong La Niña events. During La Niña years there is a higher incidence of strong winds from the South and particularly from the SW, while during the El Niño years the winds from N, E to ESE increase (Gutiérrez et al, 2016).…”

“…This coast is subject to an erosion-accretion cycle related to spring-summer and winter periods, and inter-annual variability due to atmospheric anomalies, e.g., wind direction changes and the consequent swell and littoral drift changes, associated with El Niño and La Niña events. The former is associated with accretion and the latter with erosion (Gutiérrez et al, 2016). The primarily observed wind and sealevel patterns related to this cycle are synthesised as follows:…”

“…− Under both current and future (centred in 2030) Representative Concentration Pathways climate scenarios (RCPs), there is a slight increase of SE winds along the Uruguayan coast (Nagy et al, 2015). − The frequency of days with winds higher than 8 m/s increases during spring-summer (Nagy et al, 2008a), whereas the average wind speed and anomaly slightly increase (Nagy et al, 2003;2008b) during El Niño-La Niña (Gutiérrez et al, 2016). − Southern winds play a vital role on the Uruguayan coastal dynamics, but with different effects depending on the synoptic conditions and fetch associated with wind speed (Nagy et al, 2008a;Gutiérrez et al, 2015;2016;Verocai et al, 2015).…”

“…According to Gutiérrez et al (2016), three storm events coinciding with elevations of 2.11 m Above Mean Sea Level (AMSL) were found corresponding with average daily Southern winds (S) ranging from 24 m/s to 31 m/s. These events can overcome most of the prism beach in most of the study area.…”