KEY INSIGHTS

• Within just 3 weeks between Jan 27 and Feb 16, there were 15 x 90mm+ rainfall days recorded in towns and cities across the North Island (and this doesn’t include multiple stations taken out by the floods for multiple days)
• The locations hit by 90mm+ days include:
  • Whangarei Airport (142 + 160mm in consecutive days)
  • Whangaparoa (106mm)
  • Whenuapai (230mm)
  • Auckland Airport (258mm, which was the highest single day recorded)
  • Whitianga Airport (121mm)
  • Tauranga Airport (104mm)
  • Rotorua Airport (101mm)
  • Tolaga Bay (126mm, + 57mm the next day too)
  • Taupo Airport (113mm)
  • Napier Airport (97mm on Jan 28 then 103mm + 96mm on Feb 13-14)
  • Castlepoint (95mm)
  • Wainuiomata (96mm)
• In addition to this, many areas received consecutive 50mm+ days and significant flooding.
• See https://thefacts.nz/environment/auckland-rainfall-flooding-january-2023/ for more insights on the Auckland flooding January 27

KEY QUESTIONS

1. Were the forecasts accurate enough?
2. Should rainfall be presented in cm not mm, since cm is more commonly used and more easily understood in everyday language?
3. Were the emergency alerts set at the right levels and sent at the right times?
4. Do we have sufficient flood maps, simulations, and exit plans?
5. Do we need to invest more in stormwater infrastructure, including stronger stopbanks and forestry slash solutions?
6. Is this a 1-in-200-year storm, or our new normal?

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Full data analysis
Please contact us if you would like the full analysis.

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Notes:

• We decided to only show the North Island rainfall, and not the South Island or other islands, due to the recent floods being located in the North Island.
• Rainfall is typically measured in mm due to the (usually) small numbers.
• Sometimes, an hourly reading fails so that day’s data does not show in the MetService graphs or Past Weather pages. This could be due to power issues, cellular issues, equipment failure, or deletions due to calibrations being performed at that time.
• We have presented all available publically available MetService data where there are sufficient data records available:
  • Some estimations were made for some locations with low rainfall and missing data:
    • Tolaga Bay Feb 15-16. We estimated 5mm and 3mm in line with Napier Airport’s low rainfall for those days.
    • Whitianga Airport Feb 13-14. We estimated 57 + 36mm being the average of Auckland Airport and Tauranga Airport on either side. There was no data for other stations on the Coromandel Peninsula, and it was late January and not February when Whitianga was hit hardest, so we decided it was best to show this information.
    • Whenuapai Jan 28 and 30, and Feb 10-12, 15-16. We used the average of Auckland Airport and Whenuapai for these lighter rainfall days.
    • Whangārei Airport Feb 15. We estimated 0mm as Whangaparaoa, Kerikeri, and Kaitaia all recorded 0mm that day.
  • We could not yet present Feb 14-16 rainfall data for the following locations due to damaged weather stations or cellular connections:
    • Gisborne Airport
    • Mahia
    • Wairoa
    • Hastings
    • Takapau Plains (near Waipukurau)
      If/once this data becomes available, we can update the graph.
  • We omitted the following locations since there were already similar rainfall readings at other stations nearby: Taupō, Ohakea, Palmerston North City, Otaki, Waikanae, Kelburn.
  • We omitted the following locations due to too many data gaps and also other stations nearby: Kaikoha, Paeroa, Hāwera, Levin, Porirua City.
  • There was no past weather data for: Paihia, Dargaville, Warkworth, Kumeu, Waiheke Island, Auckland Central, Waitakere, Hunua, Manukau, Pukekohe, Thames, Ruatoria, Te Puke, Matamata , Te Awamutu, Tokoroa, Te Kuiti, Eastern Rangitaiki, Dannevirke, Martinborough, Te Horo, Judgeford, Ohariu Valley, Upper Hutt, Wellington Central, Lyall Bay.
  • There was no past rainfall data for: Kaitaia Hospital, Ardmore Airport, Napier (City), New Plymouth City, Whanganui City.
• More detailed weather station data can be obtained via http://cliflo.niwa.co.nz/. We encountered some errors, so could not analyse this data set at this time. Please note:
  • It is hard to use the GPS coordinates to determine station locations. There does not appear to be a visual map.
  • It looks like there is a free query limit too.
    We will update this information when we find out more.
• MetService also said “The Auckland Council also operate an extensive network of rain gauges across the Auckland region. Their data can be found at: https://environmentauckland.org.nz/”
• All numbers are provisional and subject to revision.

Thank you to the Factors who helped pull this together.

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SOURCE:

• Daily rainfall for towns and cities = https://www.metservice.com/towns-cities (click on the location and then Past Weather > Last 30 Days)

(c) Meteorological Service of New Zealand Limited

Licensed for use under the creative commons attribution licence (BY) 4.0

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Did we make a mistake, or have you got smarter data?  Let us know.