GESLA Background

The GESLA (Global Extreme Sea Level Analysis) project grew out of the interests of several people in learning more about the changes in the frequency and magnitude of extreme sea levels. The first formal GESLA data set (denoted GESLA-1) was assembled by Philip Woodworth (National Oceanography Centre Liverpool), Melisa Menendez (University of Cantabria) and John Hunter (University of Tasmania) around 2009 and contained a quasi-global set of 'high frequency' (i.e. hourly or more frequent) measurements of sea level from tide gauges around the world.

GESLA-1 was used first in a study of sea level extremes by Woodworth and Menendez (Journal of Geophysical Research, 2010). It has since been used in a number of other published studies of extremes including the Intergovernmental Panel on Climate Change Fifth Assessment Report.

After some years it became apparent that GESLA-1 needed updating, which has resulted in the present GESLA-2 that contains 1355 records and 39151 station-years. The three people above have been joined in GESLA by Marta Marcos (University of the Balearic Islands) and Ivan Haigh (University of Southampton).

A list of some of the published papers that have made use of either GESLA-1 or GESLA-2 is given below. It can be seen that, while the study of extreme sea levels has been the main interest, the availability of as large a quasi-global sea level data set as possible enables many other types of study, such as changes in the ocean tides. We believe that the oceanographic community needs a global data set such as GESLA, that is regularly updated and extended to include new historical data as it becomes available, and we are taking steps to see how that might be accomplished in the future.

The GESLA-2 data set was described by Woodworth et al. (2017).

GESLA Data Sets

How is GESLA constructed?

We have benefited from the fact that suitable data are now readily accessible from many national web sites, requiring only reformatting to make them available for scientific research (see the link below for the format description). In addition, we have traded on the excellent personal links that we have established though the years to ask for data that is not otherwise publicly available. These data files have also been reformatted and added to the combined set. Thirdly we have made use of the data held by the international data centres, in particular the University of Hawaii Sea Level Center. UH have done an excellent job for many years in collecting and quality controlling (QCing) sea level records, and UH information comprises over a quarter of GESLA.

At the present time we do not normally perform our own separate QC of the data we receive, we assume that some form of QC has already been undertaken by the national and other authorities. We realise that this is not a perfect situation and we intend that a subset of GESLA (perhaps the longest records) will be subject to a separate QC by us in a subsequent step.

How is GESLA data made available?

Data from the various sources mentioned above have been provided to us on the understanding that it can be copied readily to other interested users, or can be copied subject to a firm acknowledgement to the original data owner, or cannot be copied at all.

This means that we cannot at the present time make the entire data set available to everyone as we would like. Any bona fide researcher should contact gesla.help@gmail.com with an explanation of why they would like access to the entire GESLA-2 data (i.e. both the 'public' and 'private' parts). We will then decide if we can accede to the request and we will specify the terms and conditions. In practice, this will depend strongly on whether we know the researcher or know of their previous research, so speculative enquiries will almost certainly be declined.

To download that part of the data set which is public and for which there is no problem with general access, follow this link. This file is essentially the same as that described by the Identifier: doi:10.5285/3b602f74-8374-1e90-e053-6c86abc08d39 in Woodworth et al. (2017), but with a small number of corrections to station locations and other minor changes.

To download that part of the data set which is private, follow this link (use "gesla_private" as user name, and password which will be provided if access is granted).

We intend that all the data will eventually be made available via one or more of the international sea level centres.

GESLA Data Sources

There are 30 sources of data in GESLA-2. We consider 27 of them to be 'public', subject in some cases to the sources being explicitly recognised, while 3 of them are 'private'. There is one file per station and the end of the station filename indicates the source as shown below. The number of records and the number of station-years are indicated. In total there are 1355 records and 39151 station-years.

There will some duplication between sea level records provided by the different sources. In general we advise to use the longest and most recently complete record at a site with more than one. The sets of records shown as 'copied from GESLA-1' will be older records without recent data.

'Acknowledgement needed' indicates that recognition of the source of the data is required by the authority in any report or paper. That can be achieved either by an explicit mention of the authority or by pointing to this web site and table.

Where web sites are shown then they are the sources of the GESLA data. In other cases, data were made available to us directly. The 'private' data have to be specifically requested as explained above.

Public

	Right-hand part of filename <country>-<contributor>	No. records	No. station-years	Source
1	glossdm-bodc	191	3380	GLOSS Delayed Mode data copied from GESLA-1
2	*-uhslc	679	15992	from uhslc.soest.hawaii.edu
3	japan-jma	80	3072	from Japan Meteorological Agency
4	uk-bodc	46	1627	from www.bodc.ac.uk
5	usa-noaa	73	3398	from opendap.co-ops.nos.noaa.gov
6	france_med-refmar	14	216	from refmar.shom.fr - acknowledgement needed
7	spain-pde	31	460	from Puertos del Estado, Spain
8	canada-meds	26	2017	from Marine Environmental Data Service, Canada
9	egypt-noc	1	20	Alexandria data processed by NOC, UK
10	spain-ieo	10	609	from Instituto Espanol de Oceanografica, Spain
11	italy-idromare	25	557	from idromare, Italy
12	turkey-eseas	1	14	copied from GESLA-1
13	france-refmar	29	1081	from refmar.shom.fr - acknowledgement needed
14	uk-noc	5	75	from www.ntslf.ac.uk
15	sweden-smhi+	30	1185	from SMHI, Sweden - acknowledgement needed.
16	spain_atlantic-ieo	3	204	from Instituto Espanol de Oceanografica, Spain
17	germany-bsh	1	99	from Federal Maritime and Hydrographic Agency, Germany
18	finland-fmi	13	598	from Finnish Meteorological Institute - acknowledgement needed
19	nl-rws	3	135	from Rijkswaterstaat Netherlands
20	croatia-eseas	3	7	copied from GESLA-1
21	denmark-dmi	3	310	from http://www.dmi.dk/laer-om/generelt/dmi-publikationer/2013/
22	norway-statkart	6	280	from Norwegian Hydrographic Service
23	iceland-coastguard	1	45	from Icelandic Coastguard Service
24	italy-itt	1	43	from Istituto Talassographico di Trieste
25	italy-comune_venezia	1	32	from Venice Commune
26	uk+ukraine-noc	1	31	data from the Uraine Vernadsky base processed by NOC, UK
27	poland-eseas	1	42	copied from GESLA-1

⁺ These data were replaced in June 2021 on advice from SMHI. The new files have a greater total span and there are now 30 stations and 2220 station-years from this source.

Private

	Right-hand part of filename <country>-<contributor>	No. records	No. station-years	Source
28	australia-johnhunter	29	1310	copied from GESLA-1, original data from National Tidal Centre
29	australia-national_tidal_centre	47	2271	from National Tidal Centre Australia
30	croatia-university_zagreb	1	41	from University of Zagreb

"Problems" File

A text file describing current known problems with GESLA-1 and GESLA-2 is here.

Acknowledgements

Any reports or papers that make use of GESLA data should include an acknowledgement to this web site and refer to the paper by Woodworth et al. (2017). We would be grateful to be notified of such papers and, if possible, sent copies of them.

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For more information, contact: gesla.help@gmail.com.

Updated 2/9/2021