A109 Light Utility Helicopter flight with mayor Gisborne City from the air in November 2023.
Rain-weary residents of the Gisborne-East Coast region may be wondering why ordinary winter rain turned into such a devastating event over the past week.
While not as intense as the four-day Cyclone Bola disaster, the rain event over recent days was twice as long, and arrived on a district already saturated to overflowing with previous downpours including Cyclones Hale and Gabrielle.
Soil has turned to slop from one end of the district to the other, with hillsides and the roading network everywhere showing a land scarred with slips.
The rain started on June 16, with a one-day pause over the 20th and 21st, and resuming right through to yesterday.
Some nine days of rain — a depressive and seemingly never-ending drenching which fortunately did not deliver the amounts or intensity of Cyclone Bola.
By the early hours of Saturday morning, MetService’s Gisborne airport rain gauge had recorded a normal year’s worth of rain since January 1, with days to go before the end of the first six months of the year.
The 30-year “average” year has just shy of a thousand millimetres of rain — by 9am yesterday this had been exceeded.
Including harbour board records dating back to the 1870s, only three other years have had so much rain in the first six months — and all of these were before recordings started at Darton airfield.
One hundred and six years ago, the first half of 1917 recorded over 1025mm, while 1894 had almost 1090.
The wettest first half year on record is 1879, with over 1112 millimetres.
MetService communications meteorologist Andrew James was asked how a seemingly normal winter weather system could develop into the near-equivalent of a cyclone.
He says there are two reasons the weather has had such an impact — the saturated state of the soils, and a high pressure system out by the Chatham Islands stopping the weather from moving away.
Mr James says this has meant the rain system was being held up, and it has continued to drag down warm, moisture-laden air from the sub-tropics.
“The fact that the soil can’t soak up any more has caused real problems — but fortunately there have been enough breaks to allow some water to drain off.
“It has been really difficult for you people in the Tairāwhiti region — we all recognise that.
“But there is some good news on the horizon — the showers will clear over the next few days, more typical westerlies will return and deliver long dry spells into next week.”
Over the present event, rainfall totals have varied wildly, with the steep ranges catching the full force of the easterly deluge.
Some areas, particularly those inland from Gisborne such as Waikohu and Wharekopae, had similar amounts to Bola in 1988, but over the longer period.
The Coast townships have again been cut off by flooding, but the amounts were less than for Gabrielle — Ruatoria 370mm versus 545mm for Gabrielle, Te Puia Springs 498mm v 771mm and the Hikuwai gauge at Tolaga Bay 554mm v 864mm.
Further north in the heart of the ranges, Raukumara Station totalled 758mm for this event — more than the 514mm in Gabrielle, but far less than May’s amazing downpour of 1121mm.
Cyclone Bola’s heaviest rainfall was 917mm inland from Tolaga Bay.
The district council gauge at the Mata River recorded 780mm this event — more than Gabrielle’s 741.
Inland, Waipaoa Station’s gauge had 427mm this time, slightly more than in Gabrielle — while to the south, the Wharerata gauge totalled 535mm against 632 for Gabrielle.
By this morning Gisborne City’s gauge at the airport had had over 325mm for June — and is sure to set a new record since official measurements began in 1937.
The current June rainfall record for the city stands at 328mm, set in 1977.
While flooding caused evacuations at Te Karaka, and damaged a stopbank south of the town, river levels around the district did not peak to Bola or Gabrielle levels.
Nature for once was on residents’ side in that peak high tides are not until the end of the first week in July, and because there was enough time in the lulls between downpours for some water to get away.
Do we get a break from the rain?
According to the MetService outlook, yes — tomorrow and Thursday should be “OK”, but there are still a few showers around for Friday and Saturday, until those westerlies return.