Exploring ENSO Driven Extreme Sea Levels and Potential Impacts in the Guayas Delta–Gulf of Guayaquil, Ecuador

Abstract:

The largest interannual sea level variability and extremes occur in the Pacific in response to the El Niño‒Southern Oscillation (ENSO) climate fluctuation. Climate models suggest an intensification of these year-to-year sea level fluctuations due to the projected increase in frequency and magnitude of extreme El Niño and La Niña events with greenhouse warming during the twenty-first century. How ENSO driven extreme sea levels manifest across river deltas, where human population and wetland ecosystems are particularly exposed to coastal hazards, yet remains unknown. Using long-term tide records, we report on extreme sea levels during historical El Niño events across the Guayas delta‒Gulf of Guayaquil (Ecuador), the largest estuarine system on the Pacific coast of South America, in a region where El Niño effects are maximal. We observed a landward amplification of sea level anomalies across the delta during eastern Pacific El Niño events, evidenced by the quasi-doubling of sea level anomalies from the open coast to the inner delta. We found one of the highest El Niño driven extreme sea levels ever documented, reaching up to +90 cm during the 1997-1998 extreme El Niño in the inner delta. We also showed that this spatial pattern coincides with a sea-to-land gradient from a predominantly oceanic forcing at the most seaward site to meteorological forcing to sea level anomalies in the most landward site. We discuss potential implications of these results on flood exposure of coastal societies and ecosystems and highlight the particularly large vulnerability of coastal river deltas and the high need for adaptation measures under future global warming. These findings also call for pursuing efforts on climate model simulations of ENSO properties and teleconnection patterns at regional scales to improve projections of interannual sea level variability.