ANCHORS: A multi‐decadal tide gauge dataset to monitor Australian relative sea level changes

Abstract

Here, we describe a new national tide gauge-based sea level dataset for monitoring sea level changes around Australia, and the novel homogenization methodology used to develop it. Homogenization is a two-step process that involves the detection of jumps or steps in the data (inhomogeneities) followed by a correction applied to remove the change. This new dataset is called the Australian National Collection of Homogenized Observations of Relative Sea Level (ANCHORS).ANCHORS provides coastal sea levels at hourly resolution with homogenization performed on annual means. ANCHORS is intended to be a national tide gauge-based sea level dataset to monitor changes in mean sea level and resultant coastal flood frequency changes around Australia. Whilst sea levels are rising around Australia in response to global mean sea level changes, coastal water levels represent a notable gap in the suite of in situ high-quality datasets available for researchers, governments and industry. Tide gauge datasets are well suited to impact-based assessments of changes in flood frequency, duration and risk.In this regard, ANCHORS will sit alongside existing satellite-and numerical modelling-based sea level datasets to provide enhanced insights into the physical impacts of sea level rise on Australian coastlines. We have adapted established homogenization techniques to develop a national collection of homogenous long tide gauge records. The dataset comprises 38 tide gauge records from around Australia, varying in length from 34 to 123 years, with an average of 57 years.

Australian Coastal Flooding Trends and Forcing Factors

“…This study is the first to provide a national assessment of the changes in coastal flood frequencies that have been elicited from changes in Australian mean sea levels over the last 50 yr. We present updated estimates to mean sea level changes since 1966 and extend the impact‐based approaches of Hague et al. (2019) to demonstrate resultant changes in coastal flooding at locations around Australia (Hague et al., 2021). We also consider how spatial and temporal variabilities in coastal floods are influenced by tidal modulations and storm surges, building on previous work (Eliot, 2010; Haigh et al., 2014; Hunter, 2020).…”

“…To assess the effect that the adjustment of inhomogeneities undertaken in ANCHORS has on the estimation of the annual mean we repeat the above computation on the unadjusted ANCHORS data (Table S2 in Supporting Information S1). As confidence assessments could not be made to unhomogenized data (Hague et al., 2021), we analyze all years with at least 70% data availability. Considering the national weighted average, the mean sea level rise in this unadjusted data is very similar to that estimated using the adjusted data over both the 1966–2019 (1.89 mm/yr) and 1993–2019 (3.88 mm/yr) periods, indicating very little overall impact of homogenization on average trends, as might be expected.…”

“…Here, we aim to provide new insights into Australian coastal sea levels and their impacts by analyzing the new Australian National Collection of Homogenized Observations of Relative Sea Level (ANCHORS) dataset (Hague et al., 2021). This dataset provides hourly observations for 38 locations around Australia with homogenization performed on annual means.…”

“…Please refer to Hague et al. (2021) for further information on this dataset. Coastal impact data used to define flood thresholds are included in Table S1 in Supporting Information S1.…”

“…We seek to quantify the extent to which these trends are driven by greater storminess (e.g., higher, or more frequent, storm surges) and higher tides due to sea level rise. This is achieved by combining a new national homogenized relative sea level dataset (Hague et al., 2021), with a framework that is used to define impact‐based thresholds by matching reports of coastal flood impacts to the water levels at which they are reported (Section 2.3; Hague et al., 2019). Minor coastal floods are already observed frequently in many key Australian population centers, and as such robust impact‐based coastal flood thresholds can be defined.…”