Phil John Watson

The Korean Peninsula is critically exposed to impacts associated with current and projected rising mean sea-levels (MSLs) associated with climate change. Rising MSL will continue to exacerbate existing coastal hazards (e.g., typhoon-driven storm surges, tidal inundation, beach erosion, etc.). This study updates the previous 2019 national sea-level rise assessment with an additional 7 years of tidal and satellite altimetry data. Having corrected the rate of “relative” MSL rise for vertical land motion, only Busan and Ulsan tide gauge records have not experienced an increase in the rate of “geocentric” MSL rise since the 2019 Assessment. At the 95% CL, the current rate of “geocentric” MSL rise at all stations accord with recent published estimates of the rate of global MSL rise. From satellite altimetry of the sea margins around the Korean Peninsula, there has been a small (≈1%) increase in the average regional trend of sea-level anomalies (SLAs) compared to the previous assessment. The most significant trend estimates in SLAs continue to increase in margins of the East Sea (Sea of Japan) between 35° N and 40° N with increases of around 11% in the average rate of trend above the 2019 Assessment.

This paper investigates the influence of back-to-back major hurricanes “Helene” and “Milton” which devastated south-eastern regions of the USA in 2024, and the extent to which associated storm surges influenced Extreme Value Analysis (EVA) of the long ocean water level record at Key West, Florida dating back to 1913. The highest recorded storm surge of 890 mm was recorded during a major hurricane event in October 1944, approximately 56 mm higher than the peak of the surge recorded at Key West during hurricane “Wilma” in 2005. Reanalysis of 2023 published EVA results for Key West indicate that despite the devastation of “Helene” and “Milton”, the super-elevation of the ocean water surface above Mean Sea Level (MSL) recorded at the Key West tidal facility during these hurricanes were at or below that which would be expected around once per annum. The timing and location of the peak of the storm surge with high predicted tides is no more than coincidental but remain the governing factors behind realizing record-breaking water levels over the historical record.

This article conducts an extreme value analysis (EVA) of hourly tide gauge measurements at Busan, South Korea, from 1960 onwards to understand the influence of typhoon-driven surges and predicted tides that super-elevate ocean still water levels (SWLs) at Busan. The impact of the 2003 super-typhoon “Maemi” dominates the records, super-elevating the SWL above mean sea level (MSL) by 1403 mm, equating to a recurrence interval of 98 years, eclipsing the second highest measured extreme in August 1960, with a return level of around 16 years. The sensitivity testing of the random timing of high tides and typhoon storm surges reveals several near misses in recent history, where water levels attained at the Busan tide gauge could have surpassed the records set during the “Maemi” event. This paper explores the omnipresent increasing risk of continuously increasing sea level coupled with oceanic inundation associated with extreme phenomena. By integrating sea level projections (IPCC AR6), the result of the EVA provides important resources for coastal planning and engineering design purposes at Busan.

This paper provides an Extreme Value Analysis (EVA) of the hourly still water level (SWL) record at Key West, Florida dating back to 1913 to understand the statistical likelihood of the combination of high predicted tides and the more dynamic influences (predominantly hurricane induced storm surges) that can drive ocean water levels higher at the coast. The impact of hurricane ‘Wilma’ in 2005 dominates the records, producing a super-elevation of the SWL above Mean Sea Level (MSL) of 1155 mm with an estimated return period of around 147 years. This paper explores the duality of increasing risks of oceanic inundation due to extreme events and increasing mean sea level over time, whilst also providing a range of recommendations for ensuring improved predictive model fitting and robustness of EVA for SWLs measured at tide gauges. When integrated with future IPCC AR6 sea level projections, the return level plots from the EVA provide decision makers with key guidance for design, strategic planning and climate change adaptation purposes at Key West, Florida.

This paper provides an Extreme Value Analysis (EVA) of the hourly water level record at Fort Denison dating back to 1915 to understand the statistical likelihood of the combination of high predicted tides and the more dynamic influences that can drive ocean water levels higher at the coast. The analysis is based on the Peaks-Over-Threshold (POT) method using a fitted Generalised Pareto Distribution (GPD) function to estimate extreme hourly heights above mean sea level. The analysis highlights the impact of the 1974 East Coast Low event and rarity of the associated measured water level above mean sea level at Sydney, with an estimated return period exceeding 1000 years. Extreme hourly predictions are integrated with future projections of sea level rise to provide estimates of relevant still water levels at 2050, 2070 and 2100 for a range of return periods (1 to 1000 years) for use in coastal zone management, design, and sea level rise adaptation planning along the NSW coastline. The analytical procedures described provide a step-by-step guide for practitioners on how to develop similar baseline information from any long tide gauge record and the associated limitations and key sensitivities that must be understood and appreciated in applying EVA.

The potential threats to the USA from current and projected sea level rise are significant, with profound environmental, social and economic consequences. This current study continues the refinement and improvement in analysis techniques for sea level research beyond the Fourth US National Climate Assessment (NCA4) report by incorporating further advancements in the time series analysis of long tide gauge records integrated with an improved vertical land motion (VLM) assessment. This analysis has also been synthesised with an updated regional assessment of satellite altimetry trends in the sea margins fringing the USA. Coastal margins more vulnerable to the threats posed by rising sea levels are those in which subsidence is prevalent, higher satellite altimetry trends are evident and higher ‘geocentric’ velocities in mean sea level are being observed. The evidence from this study highlights key spatial features emerging in 2020, which highlight the northern foreshore of the Gulf Coast and along the east coast of the USA south of the Chesapeake Bay region being more exposed to the range of factors exacerbating threats from sea level rise than other coastlines at present. The findings in this study complement and extend sea level research beyond NCA4 to 2020.

The threat of sea level rise to the heavily populated Korean Peninsula, which contains around 15,000 km of coastline bordering open sea margins, has profound and far reaching implications. This study updates and extends previous detailed studies with the addition of a further 2 years of data to the end of 2019, providing renewed robustness to the identification of emerging threats associated with sea level rise within the warming sea margins around the Korean Peninsula. The study analyzes tide gauge records and satellite altimetry around the Republic of Korea using enhanced time series analysis techniques to detect coastal vertical land motion and current rates of rise in mean sea level to augment planning, design and risk management activities. Despite fluctuations over time at each site, the highest “relative” mean sea level at each of the seven longest tide gauge records occurs in 2019, with weak evidence of an acceleration in the increase in mean sea level around the Republic of Korea. Trends in sea surface height from satellite altimetry across this region note two discreet areas east and west of the Korean Peninsula around 37.5° N (around Ulleungdo Island and in the Gyeonggi Bay region of the Yellow Sea), where rates of rise are well above the global average trend.

Watson, P.J., 2020. Updated mean sea-level analysis: Australia. Journal of Coastal Research, 36(5), 915–931. Coconut Creek (Florida), ISSN 0749-0208.As an island nation with 60,000 km of open coastline and extensive margins of increasingly urbanised intertidal estuarine foreshores, Australia is critically exposed to the global threat posed by rising sea levels into the future. This study provides a contemporary assessment of sea-level rise around Australia to the end of 2018, based on all available tide gauge records and satellite altimetry. The study provides the first national assessment of vertical land motion (VLM) around the coast, identifying margins more prevalent to subsidence, which in turn exacerbate the localised effects of a rising global mean sea level. These areas include coastlines between Townsville and Coffs Harbour, Burnie to Port Pirie, and Fremantle to Wyndham. State-of-the-art time-series analysis techniques applied to all high-quality tide gauge records exceeding 75 years in length (four sites) enabled improved insights into the temporal resolution of current rates of rise and accelerations in mean sea level around Australia than were previously available. Averaged across these four records in 2018, approximately 40% of the “relative” velocity observed (∼2.2 ± 1.8 mm/y, 95% confidence limit [CL]) is attributable to VLM. When corrected for VLM, only the Fort Denison site exhibits “geocentric” mean sea-level velocity in 2018 exceeding 2 mm/y. The average geocentric velocity across all four sites in 2018 equates to 1.3 ± 2.0 mm/y (95% CL). Interestingly, each long record exhibits similar temporal characteristics, whereby a low point in the velocity time series occurs sometime in the period from 1970 to 1990, after which velocity increases over time to a peak occurring sometime after ca. 2010, suggesting the presence of a small acceleration (albeit not statistically different to zero at the 95% CL) in the record.

Watson, P.J., 2019. An assessment of the utility of satellite altimetry and tide gauge data (ALT-TG) as a proxy for estimating vertical land motion. Journal of Coastal Research, 35(6), 1131–1144. Coconut Creek (Florida), ISSN 0749-0208.Policy, planning, and adaptation responses to sea-level rise are being developed at increasingly localised scales, placing greater emphasis on sea-level studies to more accurately account for all vertical land motions (VLM) at tide gauge sites using technologies such as global navigation satellite systems (GNSSs). Although the spatial coverage and length of GNSS data records continues to increase in proximity to tide gauges, large tracts of the world's coastlines contain limited or no GNSS data. Various studies have investigated proxy methods of estimating VLM by trends from differenced altimetry–tide gauge techniques (ALT-TG). This study has concentrated on investigating the utility of ALT-TG techniques using so-called ‘off the shelf’ gridded satellite altimetry products (U.S. National Aeronautics and Space Administration Jet Propulsion Laboratory [NASA JPL] and Copernicus Climate Change Service [C3S]) for use in regional and local scale sea-level studies to estimate VLM. Twenty locations across the globe were analysed; these locations met specific data constraints designed to ensure the longest overlapping coverage of GNSS, altimetry, and tide gauge data, with the proximity of the GNSS record limited to within 1 km of the tide gauge. The utility of ALT-TG estimates was significantly improved by using gridded altimetry products no closer than 30 km from the open coast. When compared directly with measured GNSS solutions from NASA JPL, Systeme d'Observation du Niveau des Eaux Littorales (SONEL), and Nevada Geodetic Laboratory (NGL), both ALT-TG VLM estimates agree with the NGL GNSS solution for 19 of the 20 locations (95% confidence interval). This is significant given that the NGL estimates are derived over the longest timeframe available from all three key GNSS data repositories considered. If one considers the limitations of altimetry sea surface height measurements in the coastal zone, the results using gridded sea surface height anomaly products for ALT-TG derived estimates of VLM are extremely encouraging for sea-level research.