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<front>
<journal-meta>
<journal-id journal-id-type="publisher">EGUsphere</journal-id>
<journal-title-group>
<journal-title>EGUsphere</journal-title>
<abbrev-journal-title abbrev-type="publisher">EGUsphere</abbrev-journal-title>
<abbrev-journal-title abbrev-type="nlm-ta">EGUsphere</abbrev-journal-title>
</journal-title-group>
<issn pub-type="epub"></issn>
<publisher><publisher-name>Copernicus Publications</publisher-name>
<publisher-loc>Göttingen, Germany</publisher-loc>
</publisher>
</journal-meta>
<article-meta>
<article-id pub-id-type="doi">10.5194/egusphere-2026-4129</article-id>
<title-group>
<article-title>A hybrid machine-learning framework combining hydrodynamic simulation and tide-gauge observations for storm-surge nowcasting in the southern North Sea</article-title>
</title-group>
<contrib-group><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Wang</surname>
<given-names>Qiang</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
</contrib>
<contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Lepers</surname>
<given-names>Ludovic</given-names>
<ext-link>https://orcid.org/0009-0000-8767-7935</ext-link>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
</contrib>
<contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Culot</surname>
<given-names>Alexis</given-names>
<ext-link>https://orcid.org/0009-0003-5646-3901</ext-link>
</name>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
</contrib>
<contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Hanert</surname>
<given-names>Emmanuel</given-names>
<ext-link>https://orcid.org/0000-0002-8359-868X</ext-link>
</name>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
<xref ref-type="aff" rid="aff3">
<sup>3</sup>
</xref>
</contrib>
<contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Legrand</surname>
<given-names>Sebastien</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
</contrib>
</contrib-group><aff id="aff1">
<label>1</label>
<addr-line>Operational Directorate Natural Environment (OD Nature), Royal Belgian Institute of Natural Sciences (RBINS), rue Vautier 29, Brussels, 1000, Belgium</addr-line>
</aff>
<aff id="aff2">
<label>2</label>
<addr-line>Earth and Life Institute (ELI), UCLouvain, Croix du S 2, Louvain-la-Neuve, 1348, Belgium</addr-line>
</aff>
<aff id="aff3">
<label>3</label>
<addr-line>Institute of Mechanics, Materials and Civil Engineering (IMMC), UCLouvain, Place du Levant 2, Louvain-la-Neuve, 1348, Belgium</addr-line>
</aff>
<pub-date pub-type="epub">
<day>22</day>
<month>07</month>
<year>2026</year>
</pub-date>
<volume>2026</volume>
<fpage>1</fpage>
<lpage>27</lpage>
<permissions>
<copyright-statement>Copyright: &#x000a9; 2026 Qiang Wang et al.</copyright-statement>
<copyright-year>2026</copyright-year>
<license license-type="open-access">
<license-p>This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit <ext-link ext-link-type="uri"  xlink:href="https://creativecommons.org/licenses/by/4.0/">https://creativecommons.org/licenses/by/4.0/</ext-link></license-p>
</license>
</permissions>
<self-uri xlink:href="https://egusphere.copernicus.org/preprints/2026/egusphere-2026-4129/">This article is available from https://egusphere.copernicus.org/preprints/2026/egusphere-2026-4129/</self-uri>
<self-uri xlink:href="https://egusphere.copernicus.org/preprints/2026/egusphere-2026-4129/egusphere-2026-4129.pdf">The full text article is available as a PDF file from https://egusphere.copernicus.org/preprints/2026/egusphere-2026-4129/egusphere-2026-4129.pdf</self-uri>
<abstract>
<p>&lt;span&gt;Storm surges are a major coastal hazard that can develop within a few hours, so accurate short-term predictions are essential for early warning and emergency response. Operational hydrodynamic models remain too computationally demanding to deliver on-demand, high-frequency forecasts at the required resolution, while purely data-driven models suffer from the limited duration of tide-gauge records. We propose a hybrid machine-learning framework that combines tide-gauge observations from 22 stations along the southern North Sea coast with surge simulations from the COupled Hydrodynamical&amp;ndash;Ecological model for REgioNal and Shelf seas (COHERENS) and ERA5 atmospheric forcing. Two architectures &amp;mdash; a Transformer and a parallel LSTM+Transformer &amp;mdash; are trained on this combined input and compared against (i) the same architectures trained on gauge observations alone and (ii) the COHERENS operational baseline. For 2-hour-ahead nowcasting at 10-minute resolution, the hybrid LSTM+Transformer reaches an average root-mean-square error (RMSE) of 0.055 m (0.033&amp;ndash;0.100 m across stations), substantially better than COHERENS (0.164 m; 0.137&amp;ndash;0.185 m) and modestly better than the pure data-driven baseline (0.061 m; 0.043&amp;ndash;0.100 m); the hybrid Transformer reaches 0.096 m (0.067&amp;ndash;0.121 m). The hybrid models also reproduce the magnitude and timing of extreme events well. Applied recursively, the hybrid LSTM+Transformer degrades to an average RMSE of 0.146 m at the 12-hour horizon, remaining well below the COHERENS baseline. Inference takes less than one minute on a single GPU, making the framework directly suitable for operational nowcasting. The approach should generalize to other coastal regions with comparable observational coverage.&lt;/span&gt;</p>
</abstract>
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