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Dynamics and seasonal predictability of extreme sea level variability in the tropical western Pacific

Recurring extreme sea levels in the tropical western Pacific are a well-known aspect of the El Niño-Southern Oscillation (ENSO) with sometimes damaging consequences for vulnerable communities and coastal ecosystems. As a result of major zonal and meridional mass redistributions in the tropical Pacific, sea level in the western Pacific can either rise (during La Niña) or drop (during El Niño) by up to 20–30 cm. Whereas many studies have focused on coastal inundations during La Niña events and their economic impacts, much less is known on the equally damaging sea level drops that expose shallow reefs and can lead to catastrophic coral die-offs. These sea level drops are most extreme in the
southwestern Pacific where the events are locally referred to as ?taimasa?—
Samoan for “smelly reef”. Negative effects of taimasa on fishing yields can last
for up to several years. In spite of potential societal impacts of ENSO-related sea level variability on Pacific islands, much uncertainty remains regarding its causes, regional manifestations, and potential seasonal to interannual predictability.
We propose to study the mechanisms of interannual sea level extremes in the tropical western Pacific using a combination of tide gauge data, satellite altimeter observations, and ocean reanalyses. We will then assess the predictability of future sea level variability using the latest generation of climate models and available seasonal prediction products. Our research plan includes three particular components:

1. We will build on existing observation-based understanding of extreme sea level variability to develop a “Taimasa threat index”, indicating threatened coastal resources relative to different types of ENSO events.
2. We will develop a new framework for sea level forecasting based on a state- of-the-art coupled climate model initialized with three-dimensional ocean observations. Real-time forecasts of sea level will be produced.
3. Resulting forecasts will be served online through the NOAA-sponsored Asia Pacific Data Research Center and communicated to stakeholders.

Our proposal seeks to better understand and predict sea level variability in the tropical western Pacific. The new index of sea level variability will provide the first assessment of coastal vulnerability to low sea levels and support resilience to future climate impacts. Our project will also communicate an early warning of future sea level extremes—events, which may have devastating impacts on near- shore ecosystems and coastal communities.

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