An emergency alert was sent on 19 April. Photo: RNZ / Nik Dirga
Auckland Council has released to RNZ a detailed timeline of its response to the Easter storm last month, which saw parts of the city receive more than month's worth of rain in just over an hour.
Council's data showed the peak intensity of the Easter storm had marginally exceeded that of the Auckland Anniversary flood two years ago - with more than 100mm of rain recorded in some suburbs.
Healthy Waters' head of planning Nick Vigar described the Easter storm as a "short, sharp burst" which had an overall similar severity as the Auckland Anniversary flood - both one in 100 year weather events.
Auckland Council and MetService had been under fire for failing to issue weather alerts and warnings before the Friday night storm that saw streets and garages flooded, power outages and two people trapped in cars by floodwaters.
Information provided by the Council showed Healthy Waters received its first alert of heavy rain around 10.29pm on Friday, however, it wasn't until 12.42am on Saturday that Auckland Emergency Management issued its first warning to the public - following MetService's storm watch issued at 12.07am.
Vigar said their data showed that the most intense period was between midnight and 1am - where around 81.5mm rain fell within an hour.
According to Auckland Council, the storm on the night of 18 April and the early hours of 19 April resulted in 10 families in Mount Roskill and Whau catchment area being displaced after their homes were flooded.
They include two homes that were marked as category three properties following the Anniversary flood and Cyclone Gabrielle, that have not yet carried through with the buyout process and were flooded again.
Council received a total of 87 requests for support, and of those, 23 homes were assessed as Category 3 properties following Cyclone Gabrielle.
Healthy Waters responded to 193 stormwater related callouts between 19 and 21 April.
A timeline of council's response to the Easter storm
Friday 18 April, 10.29pm: Healthy Waters' on-call duty manager received the first automated alert when rain levels reached 15mm/hour
Friday 18 April, 11.35pm: AEM received its first alert
Saturday 19 April, 12.07am: MetService issued a severe thunderstorm watch
Saturday 19 April, 12.19am: AEM's general manager Adam Maggs sent texts to a stakeholder group, including the mayor, deputy mayor, advising them that AEM is monitoring the thunderstorm cells passing over Auckland and are in contact with Fire and Emergency (FENZ) and council's call centre to monitor the situation
Saturday 19 April, 12.37am: AEM duty team undertook its standard operating procedure - including emailing stakeholders including all elected members, monitoring FENZ callouts, rainfall gauges, liaising with Healthy Waters and council's call centre
Saturday 19 April, 12.42am: AEM issued its first weather warning to Aucklanders through social media.
Saturday 19 April, 1.35am: Maggs messaged the stakeholders group advising that the Incident Management Team is being activated due to the intense thunderstorms hitting the Mount Roskill area, and that they're looking to open a shelter there for community members.
Saturday 19 April, 4.08am: Maggs messaged the stakeholders group to advise that a Civil Defence Centre will be opened in Three Kings around 4.30am. The Emergency Response Coordination Centre was activated to monitor and coordinate with FENZ.
What are Auckland Council's own systems for monitoring rain levels?
The council has 72 telemetred rain gauges across the city. When a significant volume of rainfall is reached, automated alerts are sent to the relevant teams.
Healthy Waters, which has the lowest threshold for an alert to be triggered, is the earliest to be alerted.
- Healthy Waters gets alerted when rain reaches 15mm/hour
- Auckland Emergency Management (AEM) is alerted when rain reaches 25mm/hour
- The National Emergency Management Agency (NEMA) is alerted when rain reaches 35mm/hour
Meanwhile, there are also 168 hotspot sites that the council knows to be prone to flooding - 51 of those sites have remote cameras that can be monitored 24/7.
Healthy Waters' operations team manager for central, Phillip Johansen, said multiple rain gauges were triggered on the Friday night of the Easter storm.
The first alert received by Healthy Waters was at 10:29pm on 18 April. Alerts continued to be generated and sent through to the early hours of the morning of 19 April.
Johansen said an on-call duty manager for Healthy Waters was getting alerts and monitoring the situation, and they first made contact with AEM between 1 and 2am.
When asked why Healthy Waters didn't alert AEM when it received its first alert at 10.29pm, Johansen said their team alert AEM when dwellings begin to get flooded, but don't see it necessary to talk to AEM when some some catchments get blocked at a rain level of 15mm/hour.
Vigar said up until midnight, less than 20mm of rain fell, and it wasn't until midnight that the rain intensity ramped up.
Councillor Shane Henderson: Councils need to diversify their sources of information relating to weather, rather than rely on MetService
When RNZ shared Auckland City Councillor Shane Henderson the different rain-level thresholds for triggering automated alerts via rain gauges, he said he feels there needs to be a conversation around these "trigger points" and where improvements can be made.
Henderson said he thought the response to the storm largely went okay, but he had concerns about the issue of communication and warning to the public - including the reliance on MetService to trigger alerts to the public during weather events.
"I'm a bit concerned about that point where we're relying on metservice to make those calls before rolling things out, I just encourage us to look at that," he said.
Henderson said there needed to be a nation-wide conversation around how councils could diversify the information they rely on during the lead up to potential severe weather events.
Henderson was one of the first councillors to publicly raise concern about why weather warnings weren't issued earlier.
Speaking to RNZ this week, Henderson said his main criticism was directed at MetService's delayed warning.
He said he believed council's emergency management had done a "fantastic job" and was a stark contrast to the handling of Cyclone Gabrielle - "I think we've shown some clear improvement," he said.
When RNZ approached Auckland Council for comment on Henderson's calls, Maggs responded in a statement that the national CDEM plan - a statutory document - specifies MetService as the agency who maintains a weather forecasting service, issues weather warnings to the public, and contributes to the management of public information about weather hazards and associated emergencies.
Maggs said MetService is responsible for providing scientific advice to the National Crisis Management Centre, agencies and civil defence groups.
He added that it's also critical that the public act on the natural warning signs of flooding.
"If someone encounters rising floodwaters, they should not wait for a warning or alert but evacuate to higher ground immediately. People should also never drive, walk or swim through floodwaters," he said.
RNZ had also asked council whether it would consider giving more weight to Healthy Waters' alerts for heavy rainfall and its own rain gauge monitoring system, to trigger council's communication with the public about potential severe weather.
Council's director of resilience and infrastructure Barry Potter said in a statement that AEM had responded appropriately to the Easter storm, drawing on a complex feed of weather reports, rainfall data and network information.
"The wellbeing of Aucklanders is utmost in our planning and response, and we continue to optimise our processes, working closely with our response partners in readiness for future events," he said.
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