New Zealand Journal of Marine and Freshwater Research abstracts
Seasonal, interannual, and decadal variability of storm surges at Tauranga,
New Zealand
W. P. DE LANGE
Coastal Marine Group
Department of Earth Sciences
The University of Waikato
Private Bag 3105, Hamilton
New Zealand
email: w.delange@waikato.ac.nz
J. G. GIBB
Coastal Management Consultancy
555 Esdaile Road
RD6, Tauranga
New Zealand
email: jgibbcmc@voyager.co.nz
Abstract A database of storm surge events was constructed
for two sites in south-eastern Tauranga Harbour, New Zealand, for the period
1960-mid 1998. Storm surge events were defined as occasions when the residual
level between the predicted high tide level and recorded water level exceeded
10 cm. The residual was determined at high tide only (every 12.4 h),
with 954 storm surge events found over the 38.4-year period analysed. The
magnitude and frequency of storm surge events varied considerably between 1960
and 1997, with a marked shift evident c. 1976. The period from 1976 to 1997
corresponded to a reduced storm surge frequency and magnitude, compared to the
period 1960-76. Wavelet analysis of 125 years of wind storm annual frequencies
showed strong fluctuations at inter-decadal periods. Therefore, it is suggested
that the frequency of storm surges varies in response to a coherent
inter-decadal oscillation in surface temperature over the Pacific Ocean, known
as the Inter-decadal Pacific Oscillation (IPO), that reversed phase c. 1976.
The El Niño Southern Oscillation (ENSO) also affected the number of days
exceeding the storm surge threshold per year, with La Niña events being
associated with more storm surge days. The presence of significant decadal
variations indicates that annual exceedence probability distributions may
misrepresent the storm surge hazard. The available data indicates that there
are extended periods when the IPO increases the hazard, and others when the
hazard is decreased. Existing analyses of storm surge hazard for the Bay of
Plenty have largely been based on data obtained during a period of reduced
hazard. Conditions that were associated with larger and more frequent storm
surges during 1960-76 may be expected to prevail again over the next few
decades.
Keywords storm surge; sea level; climate change; wind storms;
El Niño-Southern Oscillation; Inter-decadal Pacific Oscillation;
Tauranga Harbour
M99049
Received 6 September 1999; accepted 13 December 1999
PDF file of entire paper: medium quality (1208K); (scanned from paper original: notes about this process)
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