Review of the Tsunami Evacuation 2017

agency is CDEM
Group
10 Decision Making “As referred to in the Guide, on
receiving a PTWC message,
MCDEM works with a panel of
scientists to determine the risks
and consider what information
should be issued through the
national warning system.”
However, during events that meet pre-determined thresholds, MCDEM may issue national
warnings and advisories for any event which threatens people and property, for which CDEM is
the lead agency. In this event, tsunami waves of a significant height (2.5 draw-down on tide
gauges) were already recorded, they would likely continue for multiple hours and may still have
not yet arrived in other parts of New Zealand further from the earthquake. Therefore, MCDEM
took the step of using the National Warning System to issue a specific message regarding a threat
on land and advising evacuation. It is acknowledged that national warnings from MCDEM to CDEM
Groups which are then distributed to the public cannot be assumed to be delivered before the
first tsunami waves arrive. This is explicitly stated in the Guide to the National CDEM Plan the
Tsunami Advisory and Warning Plan as noted in the “Review of the tsunami evacuation” draft
report.
GNS Science may convene a Tsunami Experts Panel to provide advice to MCDEM for regional and
distant source events. MCDEM does not “work with” the panel, and the panel would not be
involved providing advice for MCDEM for initial warnings during local source events.
Group establishing its own tsunami
panel
Timing and contents of national
warning messages
The National CDEM Plan, The Guide to the National CDEM Plan and the Tsunami Advisory and
Warning Plan describe the role of the Tsunami Experts Panel in providing advice to MCDEM at the
national level during tsunami events.
MCDEM does not support Groups developing alternative expert panels that operate during events
to second-guess the official national advice provided by the Tsunami Experts Panel of New
Zealand.
For local source events this is particularly problematic as clear scientific data is difficult to access,
and the time period for action is compressed. MCDEM does support the use of tsunami scientific
advice in the development of tsunami hazard maps and evacuation zones and pre-event tsunami
planning, but consultation of scientists by Groups during local source tsunami events will likely be
counter-productive. When national advice is that there is a land threat and the Group is providing
alternative information to the public, this will subvert the objective of a consistent response and
will reduce public trust and confidence in civil defence emergency management.
MCDEM acknowledges that advising evacuation is a best-judgement precautionary measure
during local source events when earthquake and tsunami monitoring instrument readings may be
66