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In this section more details are given about the variables (Table 2-2).
Table 2-2: Overview and description of variables for water level change indicators: tidal indicators.Anchor table4 table4
Variables | |||
Long Name | Short Name | Unit | Description |
Mean sea level | msl | m | The average water level of a 30-year tide-only simulation. This includes the interaction effects with tides and the sea level rise over the 30-year period simulated. Storm surge caused by atmospheric forcing is not taken into account. Please refer to Appendix I for details on the vertical datum. |
Highest astronomical tide | HAT | m | Highest Astronomical Tide (HAT) is the elevation of the highest predicted astronomical tide expected to occur at a specific location over the datum (i.e. MSL). HAT is calculated as the maximum (minimum) over the 30-year simulation period. All tide variables are derived from a tide-only simulation with GTSM. Please refer to Appendix I for details on the vertical datum. |
Lowest astronomical tide | LAT | m | Lowest Astronomical Tide (LAT) is the elevation of the lowest predicted astronomical tide expected to occur at a specific location over the datum (i.e. MSL). LAT is calculated as the minimum over the 30-year simulation period. All tide variables are derived from a tide-only simulation with GTSM. Please refer to Appendix I for details on the vertical datum. |
Annual mean lowest low water | MLLW | m | Annual average of the lowest low tide of each tidal day (25-hour window) including sea level rise. Storm surge caused by atmospheric forcing is not taken into account. Please refer to Appendix I for details on the vertical datum. |
Annual mean highest high water | MHHW | m | Annual average of the highest high tide of each tidal day (25-hour window) including sea level rise. Storm surge caused by atmospheric forcing is not taken into account. Please refer to Appendix I for details on the vertical datum. |
Tidal range | TR | m | Average tidal range observed over the 30-year period simulated. Please refer to Appendix I for details on the vertical datum.[[ |
Table 2-3: Overview and description of variables for water level change indicators: extreme-value indicators and probability indicators including changesAnchor table5 table5
Total water level/surge level for different return periods with confidence intervals | Water level/surge level return periods | m | Total water level and surge level for the following return periods: 1, 2, 5, 10, 25, 50, 75 and 100 years. In addition to the best fit, a low bound (5th percentile) and high bound (95th percentile) are provided. Total water level and surge level simulations are forced by ERA5 reanalysis and the HighResMIP ensemble. Total water levels include (changes in) tidal levels, surge levels and interactions, but with sea level rise removed. Surge level are defined as the difference between the tide-only and the total water level simulations, and include (changes in) surge levels and interactions. |
Total water level/Surge level for different percentiles | Water level/Surge level percentiles | m | Total water level and surge level for the following percentiles: 5th, 10th, 25th, 50th, 75th, 90th and 95th. Simulations are forced by EAR5 reanalysis and the HighResMIP ensemble. Total water levels includes (changes in) tidal levels, surge levels and sea level rise. Surge level are defined as the difference between the tide-only and the total water level simulations, and include (changes in) surge levels and interactions. |
Absolute change of total Water level/surge level for different percentiles | Absolute change Water level/surge level percentiles | m | The absolute change of total water level/surge level for the following percentiles: 5th, 10th, 25th, 50th, 75th, 90th and 95th. The absolute change is computed for the HighResMIP ensemble for 2021-2050 and 1951-1980, using 1985-2014 as the reference period. |
Relative change of total Water level/surge level for different climate model and different percentiles | Absolute change Water level/surge level percentiles | % | The relative change of total water level/surge level for the following percentiles: 5th, 10th, 25th, 50th, 75th, 90th and 95th. The relative change is computed for the HighResMIP ensemble for 2021-2050 and 1951-1980, using 1985-2014 as the reference period. |
Table 2-4: Overview and description of variables for water level change indicators: Ensemble statistics for extreme-value and probability indicatorsAnchor table6 table6
Total Water level/surge level ensemble standard deviation for different percentiles/return periods | Water level/surge level ensemble std percentiles/return periods | m | Standard deviation of total water level/surge level across the five members of the HighResMIP ensemble for the following percentiles: 5, 10, 25, 50, 75, 90, 95; and return periods: 1, 2, 5, 10, 50, 75 and 100 years. See the variable description to see how the percentiles and return periods are defined. |
Total Water level/surge level ensemble range for different percentiles/return periods | Water level/surge level ensemble range percentiles | m | Range of the total water level/surge level (differences between maximum and minimum value) across the five members of the HighResMIP ensemble for the following percentiles: 5, 10, 25, 50, 75, 90, 95; and return periods: 1, 2, 5, 10, 50, 75 and 100 years. See the variable description to see how the percentiles and return periods are defined. |
Total Water level/surge level ensemble median for different percentiles/return periods | Water level/surge level ensemble median percentiles | m | Median of total water level/surge level across the five members of the HighResMIP ensemble for the following percentiles: 5, 10, 25, 50, 75, 90, 95; and return periods: 1, 2, 5, 10, 50, 75 and 100 years. See the variable description to see how the percentiles and return periods are defined. . |
Total Water level/surge level ensemble mean for different percentiles/return periods | Water level/surge level ensemble mean percentiles | m | Mean of total water level/surge level across the five members of the HighResMIP ensemble for the following percentiles: 5, 10, 25, 50, 75, 90, 95; and return periods: 1, 2, 5, 10, 50, 75 and 100 years. See the variable description to see how the percentiles and return periods are defined. |
Number of models that a positive change in total water level/surge level for different percentiles/return periods | Water level/surge level ensemble positive count | - | The number of members (out of 5) of the HighResMIP ensemble that show an increase in total water level/surge for the following percentiles: 5, 10, 25, 50, 75, 90, 95; and return periods: 1, 2, 5, 10, 50, 75 and 100 years. See the variable description to see how the percentiles and return periods are defined. |
Number of models that a negative change in total water level/surge level for percentiles/return periods | Water level/surge level ensemble negative count | - | The number of members (out of 5) of the HighResMIP ensemble that show a decrease in total water level/surge for the following percentiles: 5, 10, 25, 50, 75, 90, 95; and return periods: 1, 2, 5, 10, 50, 75 and 100 years. See the variable description to see how the percentiles and return periods are defined. |
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GTSM is the backbone of the global water level change time series and indicator products, and the validation of the model is thus key to the product validation. The GTSM model has been thoroughly calibrated and validated based on tide gauge observations, satellite products, and comparison with other hydrodynamic models. Table 2-6 provides a summary of the key references and description of the results. A summary is provided below.
Table 2-6: Key references of GTSM validationAnchor table8 table8
Reference | Description |
Muis, S., Verlaan, M., Winsemius, H. C., Aerts, J. C. H., & Ward, P. J. (2016). A global reanalysis of storm surges and extreme sea levels. Nature Communications, 7(1), 1-12, doi:10.1038/ncomms11969 | Validation of GTSM2.0 for the modelling of storm surges and estimation of return periods. Results show good agreement with observations. Storm surges, especially those induced by tropical cyclones, are slightly underestimated; this is mainly due to the resolution of the meteorological forcing. |
Dullaart, J.C.M., Muis, S., Bloemendaal, N. & Aerts, J. C. H. (2020). Advancing global storm surge modelling using the new ERA5 climate reanalysis. Climate Dynamics 54, 1007–1021, doi:10.1007/s00382-019-05044-0 | Evaluation of the performance of GTSM3.0 for the global modelling of storm surges for historical extreme events, and the advances due to ERA5 climate reanalysis |
Muis, S., Apecechea, M. I., Dullaart, J., de Lima Rego, J., Madsen, K. S., Su, J., Kun, Y. & Verlaan, M. (2020). A High-resolution global dataset of extreme sea levels, tides, and storm surges, including future projections. Frontiers in Marine Science, 7, 263, doi:10.3389/fmars.2020.00263 | Validation of GTSM3.0 for application to climate change projections. Comparison against observations shows a good performance with observed sea levels demonstrated a good performance with the annual maxima having mean bias of -0.04 m. |
Wang, X., Verlaan, M., Apecechea, M. I., & Lin, H. X. (2021). Computation‐Efficient Parameter Estimation for a High‐Resolution Global Tide and Surge Model. Journal of Geophysical Research: Oceans, 126(3), e2020JC016917. | Description of the calibration of the GTSM. Result show that the accuracy of the tidal representation can be improved significantly at affordable cost. |
Irazoqui Apecechea, M., Rego, J., Verlaan, M (2018) GTSM setup and validation. Project report C3S_422_Lot2_Deltares - European Services | Description of the calibration of the GTSM. |
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