Non-stationary extreme value models to account for trends and shifts in the extreme wave climate due to climate change |
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| Institution: | 1. Department of Civil and Environmental Engineering, Old Dominion University, Norfolk, 23455, VA, USA;2. Department of Civil and Environmental Engineering, Michigan Technological University, Houghton, 49931, MI, USA;3. Department of Hydraulic Engineering, Tongji University, Shanghai, 200092, China;1. Environmental Hydraulics Institute, IH Cantabria, Universidad de Cantabria, Spain;2. Institute of Marine Sciences, University of California, Santa Cruz and The Nature Conservancy, United States;1. Hydraulics Laboratory, Division of Hydraulics and Environmental Research, Department of Civil Engineering, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece;2. Department of Meteorology and Climatology, School of Geology, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece;1. Air Force Support Command, Hellenic Air Force, Elefsina Air Base, 192 00 Elefsina, Greece;2. Department of Water Resources and Environmental Engineering, School of Civil Engineering, National Technical University of Athens, Iroon Polytechniou 5, 157 80 Zografou, Greece;3. Department of Civil Engineering, Engineering Faculty, Naresuan University, Nakhonsawan – Phitsanulok Rd., 650 00 Phitsanulok, Thailand |
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| Abstract: | The extreme values of wave climate data are of great interest in a number of different ocean engineering applications, including the design and operation of ships and offshore structures, marine energy generation, aquaculture and coastal installations. Typically, the return values of certain met-ocean parameters such as significant wave height are of particular importance. There exist many methods for estimating such return values, including the initial distribution approach, the block maxima approach and the peaks-over threshold approach. In a climate change perspective, projections of such return values to a future climate are of great importance for risk management and adaptation purposes. However, many approaches to extreme value modelling assume stationary conditions and it is not straightforward how to include non-stationarity of the extremes due to for example climate change. In this paper, various non-stationary GEV-models for significant wave height are developed that account for trends and shifts in the extreme wave climate due to climate change. These models are fitted to block maxima in a particular set of wave data obtained for a historical control period and two future projections for a future period corresponding to different emission scenarios. These models are used to investigate whether there are trends in the data within each period that influence the extreme value analysis and need to be taken into account. Moreover, it will be investigated whether there are significant inter-period shifts or trends in the extreme wave climate from the historical period to the future periods. The results from this study suggest that the intra-period trends are not statistically significant and that it might be reasonable to ignore these in extreme value analyses within each period. However, when it comes to comparing the different data sets, i.e. the historical period and the future projections, statistical significant inter-period changes are detected. Hence, the accumulated effect of a climatic trend may not be negligible over longer time periods. Interestingly enough, such statistically significant shifts are not detected if stationary extreme value models are fitted to each period separately. Therefore, the non-stationary extreme value models with inter-period shifts in the parameters are proposed as an alternative for extreme value modelling in a climate change perspective, in situations where historical data and future projections are available. |
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| Keywords: | Ocean waves Extreme values Climate change Ocean engineering Maritime safety Marine design |
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