Waikato River catchments are extremely vulnerable after record rainfall.
The Waikato River’s catchments are extremely vulnerable ahead of the winter season.
Regional resilience team leader Rick Liefting, who wrote a report on the summer storm events for the council’s Integrated Catchment Management Committee, says the game has changed with regard to being able to predict the impacts of rainfall events on our catchments and a precautionary approach is needed heading into winter.
“What we have been able to do in the past is to correlate a particular ARI – an average return interval – such as a 20-year event, and understand the likely impact of such an event, like how much flooding we may see ... but that’s now changed because of our very saturated catchments,” said Liefting.
“We had a significant amount of rain – more than normal – in the second half of last year, so our catchments were already quite saturated before the events of cyclones Hale and Gabrielle and Auckland Anniversary weekend.
“Since then, we’ve had more events, and each successive event changes our catchments to the extent that we’re now seeing larger impacts from lower rainfall events. That’s likely to continue for the remainder of this winter season, and perhaps beyond as well.”
Rainfall data captured and available on the council’s Environmental Data Hub shows record rainfall totals have been reached since the start of the year at gauges sited at the Pinnacles, Waitanguru and Whangamarino. The Pinnacles already reached the historical annual average in early May 2023.
Data from NIWA shows the soil moisture deficit across much of the Waikato is at field capacity, meaning saturated, and in some instances at “water surplus”, for example, across much of the Coromandel Peninsula and in the lower Waikato catchment.
Liefting said the seasonal outlook to July, also produced by NIWA, forecasted rainfall to be “above” or at “normal” levels.
“We are expecting to have a wet winter and the impacts are still uncertain in terms of how our catchments will respond and what impacts we might see.
“Given it’s still very much a waiting game in terms of what events are coming, the council is focusing on being well prepared and informing our communities about what to expect.”
As a result, the council’s online Flood Room Live, a key communications portal for rain events and flood impacts, has been live for quite a while.
“We’re constantly monitoring the situation because rainfall events, even if they are not accompanied by a heavy rain watch or warning, are something of a concern; even the scattered thunderstorms are a concern for particular areas.”
Responding to questions about whether this was the new normal, Mr Liefting said: “The answer is we’re not sure. If we look at the soil moisture and where we were last year, which was very dry, no one was saying we’d be in this position this year. That’s where climate changing is starting to show – we are getting these extremes starting to come through, and they’re becoming more intense and frequent.”
Committee chair and Waihou councillor Robbie Cookson said the information presented to the committee was sobering but reflected the reality for many communities.
“Some of us are feeling like we’re in a state of emergency all the time. My farm is wet and it doesn’t go away; every rainfall is an event at the moment.”
Waikato Regional Council integrated catchment management director Greg Ryan says the council was having many conversations with its stakeholders about resourcing and prioritising work resulting from the summer storms, and recovery would be a multi-year programme.
“We could be in for an exceptional winter, so now is the time to plan ahead and be prepared.”
Waikato Civil Defence Group welfare manager Sia Tanaki says the recent wet weather events have brought members of communities closer together in many areas.
“The more that people are involved in their communities, the better we will all be whatever comes our way this year,” she says.
She encourages people to use the Waikato Regional Hazards Portal to see if their homes and businesses are in areas susceptible to flooding.
“If so, find out from your local district or city council how they’ll alert you if you need to evacuate.”
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