Recently increased tropical cyclone activity and inferences concerning coastal erosion and inland hydrological regimes in New Zealand and Eastern Australia |
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| Authors: | Patrick J Grant |
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| Institution: | (1) Water and Soil Division, Ministry of Works and Development, Napier, New Zealand |
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| Abstract: | For the area bounded by 0–35 °S latitude and 105 °E–105 °W longitude a significant increase of tropical cyclone frequency
occurred about 1954–55 and this regime persisted throughout the 1960s and 1970s. Probably this frequency increase was accompanied
by an increase of cyclonic storm intensity. It was related to an atmospheric pressure regime change over Australasia which
commenced in early 1954.
Tropical cyclones produce large rainfall amounts and strong winds which generate high-energy sea waves. Severe damage can
result on land and at sea. However, much recently recorded damage has resulted from extra-tropical cyclones. Therefore it
is postulated that extra-tropical cyclones also increased in frequency after the mid 1950s and that both types of cyclone
contributed to a significant increase in total storminess.
In eastern Australia and around both islands of New Zealand a major coastal regime change occurred in the 1950s and has persisted
to the present;erosion has been the dominant process. In eastern Australia there was a significant increase in the magnitude
of river floods after the late 1940s. After the mid 1950s most of the North Island of New Zealand experienced the wettest
years of this century which caused large closed lakes to reach the highest levels for several centuries. Throughout the North
Island the majority of the greatest recorded stream floods of this century have occurred during the 1950s, 1960s and 1970s.
And in forested mountain areas of the North Island the average rate of erosion and alluvial sedimentation increased markedly
after the mid 1950s.
The regime change of each natural phenomenon is explicable in terms of increased storminess since the mid 1950s. Consequently
it is hypothesised that the coastal and inland environmental regime changes discussed were either initiated or accentuated
after the mid 1950s as a result of increased activity of both tropical and extra-tropical cyclones.
Some further studies, necessary to test the links in the overall hypothesis, are mentioned. |
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