Sea Level Variability Around the New Zealand Coast PDF Download

Author: Prajakta Niphadkar
Publisher:
ISBN:
Category : Coastal zone management
Languages : en
Pages : 127

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Book Description
Regional sea levels vary considerably more than the global mean, and these variations affect communities and developments near coastal floodplains. Sea level variability is particularly relevant to New Zealand, a dynamic, coastally-dominated landscape located in the south Pacific Ocean. This study investigates the low-frequency variability in relative and absolute mean sea level around New Zealand's coastlines, using observed data from tide gauges and satellite altimetry, and simulated sea level from a high-resolution, eddy-resolving ocean circulation model, the Ocean Forecasting Australia Model 3 (OFAM3). Temporal signals in tide gauges are extracted using Ensemble Empirical Mode Decomposition (EEMD), an adaptive time-frequency analysis technique that includes monotonically time-varying long-term trends. Spatial variability in sea level is assessed using an Empirical Orthogonal Function (EOF) analysis on both altimeter and OFAM3 sea levels. The OFAM3 sea levels are tested with a range of techniques to compare the simulation with both temporal and spatial observations of sea level variability, in order to assess its suitability as a tool for locally-relevant future sea level projections. The results show evidence of significant interannual signals in temporal sea level, and distinct associations with the El Niño Southern Oscillation (ENSO) in spatial patterns. The analysis of longterm sea level behaviour using the EEMD reveals no significant accelerations or decelerations. Single spatial patterns (the first EOFs) of sea level in the altimeter and OFAM3 explain high proportions (73.4% and 82.2%, respectively) of total variance in sea level along the coasts. The patterns also highlight the northwest coast as a hotspot for greater magnitudes of variability. Evaluation of the OFAM3 reveals that it compares very well with absolute mean sea level data from the satellite altimetry, and adequately simulates interannual signals observed within the tide gauges. The OFAM3 is recommended for modelling future sea level that is more detailed and better describes sea level at the coast than coarser global models. This study reveals major gaps in relative sea level information by the lack of adequate tide gauge data around the country, particularly along the west coasts, and non-uniformity in the existing spatial coverage. Furthermore, it highlights the need for continued GPS monitoring at tide gauge sites in order to provide improved estimates of vertical land motion for future analyses.