Effects of low-frequency climatic-oceanic oscillations on small rivers and their impact on coastal erosion

Abstract

This study searched to determine whether recent morphological changes at Palomino Beach were attributable to oceanographic variables, or there was a relationship between the discharge of nearby rivers and its morphodynamic response. By analyzing satellite images and changes in the coastline, a notable period of erosion was identified (2012–2022) with rates between −0.20 and −9.39 m year⁻¹, contributing to an area loss of up to 10.20 ha (primarily at the river mouth). Although factors such as current magnitude, wave height, and sea level rise (climate change) influence coastal erosion, the research suggests that they had an insignificant impact on the observed retreat. Otherwise, the characterization of the temporal variability of river discharge showed that the Palomino River went from high streamflows during 2000–2009 to low streamflows during 2010–2021. Therefore, sediment discharge decreased by up to ∼50 %, explaining the consequent erosive process. These changes are not indicative of a long-term trend; instead, they appear to result from the potential combined influence of interannual and interdecadal/low-frequency oscillations (periods between 19 and 23 years) on streamflow variability; in this case, the superposition of oceanographic-atmospheric processes such as the Pacific Decadal Oscillation and the El Niño Southern Oscillation showed high correlations and coherence. The findings underscore the importance of integrating the management of small river watersheds into coastal planning. Additionally, incorporating the hydrological behavior of these rivers (fluvial discharge) will enhance our understanding of morphological changes in the coastal zone.