The early warning system sends alerts to people's phones based on flood warning data collected from river level recording sites on the banks of the local rivers.
The improvements would solidify the accuracy and timeliness of warnings, given different storm trajectories and weather conditions, and explore innovative ways to keep residents up to date, focusing on enabling easy access for all residents.
This would include residents from different age, ethnic and linguistic groups with variable internet and telephone access in urban, town and rural settings, the strategy said.
Advancements to the evacuation system would include applying lessons learned from recent evacuation orders and processes along Anzac Parade and the wider region.
"The high turnover of people [in the Anzac Parade area] and the clear evidence people are not all on the same page and do not have shared understanding about this means there is much more work to continue to be done on that front," Glavovic said.
Another recommendation outlined was a focus on ways to enable a buyout programme with or without community-based relocation, which was part of the medium (10-50 years) to long-term (50-100+ years) plan.
"But given the context of the work underway to produce national legislation, it's all but impossible to commit to detailed elaboration of a plan for the medium to long term," Glavovic said.
"Particularly around the question of who pays and what the Government's contribution is."
The climate adaptation legislation is expected to be released by the end of 2023.
Glavovic said raising the houses was much less of an option than originally predicted due to the "eye-watering" costs.
The strategy outlined the cost to raise a house less than 100m2 by 1m would cost between $300,000 and $540,000.
With that, Glavovic said there remained a number of currently unanswerable questions.
These questions included who the most exposed and vulnerable in the area were and how to prioritise interventions in light of that, what the potential contribution from the Government would be, what to do about renters who may not be able to afford to explore alternatives, and what to do when insurance coverage becomes unaffordable or withdrawn.
He said although there had been an expected increase in insurance premiums, no one had been denied insurance in flood-prone areas of Whanganui due to risks of flooding.
"At present, residents have a one in 30-year protection and essentially rely on evacuations, warnings and insurance," Glavovic said.
"In a one in 50-year flood, 34 homes would take in an excess of a metre of water with around 108 affected homes."
In a one-in-100-year flood, around 40 homes would take in more than a metre of water and about 122 homes would be affected, he said, and in a one in a 200-year flood, around 50 homes would take in more than a metre of water.
The strategy stated the magnitude and frequency of floods is expected to increase.
Other recommendations included improved controls on nuisance flooding including ongoing work on the Matarawa Stream diversion, and maintenance practices, preparation of floodproofing guidance and investigation of public-private partnership options for implementing household floodproofing.
"This is a ticking time bomb, and what will be on [council's] watches will be the prospect of loss of life. And that changes everything," Glavovic said.
"The real costs are indirect. The cost of lives, loss of culture and environment and place."
