The extraordinary flooding that occurred in Auckland on the night of January 27, the eve of the city’s anniversary weekend, was caused by rainfall that was literally off the chart.
Over the course of 24 hours, 249 mm of rain fell – well above the previous record of 161.8 mm. a Declared a state of emergency Late in the evening.
It took a huge toll in Oakland, with two lives One person was reported dead and two others are missing. Damage to homes, cars, roads and infrastructure will run into the millions of dollars.
While looking through the photos on social media on Friday night, I thought to myself I’ve seen these kinds of photos before. But they are usually from North America or Asia, or perhaps from Europe. But this was the largest city in New Zealand. No place is safe from harsh weather these days.
how did that happen
The heavy rains came from a storm in the northern Tasman Sea linked to a moisture source from the tropics. This is what meteorologists call the “atmospheric river”.
The storm was slow moving because it was threatened to the south by a huge (high) typhoon that stopped it from moving quickly across the country.
Severe thunderstorms developed in the main band of rain, in the unsettled air over the Auckland area. This resulted in torrential rain, with MetService figures showing that Auckland Airport received its average monthly precipitation for January in less than an hour.
However, the type of storm that caused chaos wasn’t particularly noticeable. Many similar storms have passed through Auckland. But as the climate continues to warm, so does the amount of water vapor in the air.
I am confident that climate change contributed greatly to the sheer volume of rain that came so quickly in Auckland this time.
Warmer air means more water
There will be careful analysis of historical records and many simulations using climate models to determine the scope profitability period from this flood (certainly in hundreds of years at least, in terms of our past climate).
How much climate change contributes to total precipitation will be part of these calculations. But it is clear to me that this event is exactly what we would expect as a result of climate change.
New Zealand’s first Climate Adaptation Plan is a good start, but critical questions about cost and timing must be answered
One degree of air warming translates, on average, to approx Water vapor increased by 7%. in that air. The world and New Zealand have experienced more than one degree of warming in the last century, and we have measured the increased water vapor content.
But when a storm comes along, it can translate to more than 7% more precipitation. Air “converges” (is drawn inward) near the Earth’s surface in the form of a storm system. So all that moist air is gathered together, and then “squeezed” to deliver rain.
A severe thunderstorm is the same thing on a smaller scale. Air is sucked in from ground level, rises and cools rapidly, losing much of its moisture in the process.
While the atmosphere now contains 7% more water vapor, this affinity for air masses means that rain showers can be 10% or even 20% heavier.
exceed the capacity of rainwater drainage systems
National Institute of Water and Atmosphere (Niwa) estimates That over Auckland, 1 degree of warming translates into a 20% increase in precipitation for one hour, for about one event in 50 years.
The longer we keep warming the climate, the more intense the precipitation will be.
Given what we’ve already seen, how can we adapt? Floods occur when storm water cannot drain away fast enough. So what we need are bigger drains, bigger rainwater pipes and rainwater drainage systems that can handle such extremes.
The country’s rainwater drainage system was designed for the climate we’re used to – 50 or more years ago. What we need is a storm water system designed for the climate that we have now, that we will have 50 years from now.
As seas rise and storms intensify, who will pay for New Zealand’s most vulnerable coastal real estate?
Another part of the response could be to ‘soften’ the urban environment. Concrete and bitumen surfaces force water to remain on the surface, to collect and flow out.
If we can rediscover some of the streams that have been channeled, and recreate some of the wetlands between built-up areas, we can create more. Spongy surface environment More naturally able to handle heavy rainfall. These are the responses we need to think about and act on now.
We also need to stop burning fossil fuels and reduce global emissions of carbon dioxide and other greenhouse gases as quickly as possible. New Zealand has emissions reduction plan – We need to see its impact this year. Every country should follow suit.
As I said at the beginning, no society is immune from these extremes and we must all work together.