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2017 a year of extreme weather – Expert Reaction

Posted in Expert Reactions on January 8th, 2018.

Niwa has released its annual climate summary for 2017, which it says was a year of weather extremes.

Satellite image of the Tasman tempest storm. The Cooperative Institute for Research in the Atmosphere

While the year started off wet, with the Tasman Tempest and Ex-Tropical Cyclones Debbie and Cook contributing to record amounts of rain, a dry end to the year had parts of the country recording their driest Novembers on record.

The SMC asked experts to comment on the climate summary. Please feel free to use these comments in your reporting.

Professor James Renwick, School of Geography, Environment and Earth Sciences, Victoria University of Wellington, comments:

“The NIWA climate report summarises a mixed bag of weather and climate extremes such as we often see in New Zealand. A pattern that stands out is the very dry conditions at each end of the year, with some very wet conditions in between. As the climate continues to change, this is exactly what we expect to see more of, as ‘the wet get wetter and the dry get drier’. As time goes by, storms are more likely to dump heavy rains while dry spells are more likely to last longer and suck more moisture out of the soil. The big storms in March and April dumped very heavy rains over parts of the North Island, including the flooding of Edgecumbe by the Rangitāiki River. A little later in the year, a July storm gave Oamaru its wettest day on record – three times the previous record!

“The year 2017 came in as the fifth-warmest on record for New Zealand over the past century. All five of the warmest years have occurred in the past 20 years, consistent with the greenhouse-warming trend that we see globally. Local pressure patterns helped a bit, with slightly more warm northerly winds than normal as a result of higher pressures to the east and south of the country. Even though 2017 was a warm year overall, the higher pressures and lighter winds helped ensure some cold nights, so plenty of cold extremes as well, and less windy days in Wellington!

“The year has ended dramatically with a very dry spell over much of the country, and rapid warming of sea surface temperatures in the Tasman Sea and around New Zealand. The north Tasman Sea has had above-average sea surface temperatures every month for the past three years, providing extra energy for north Tasman storms such as the one that roared through over the past week.”

Dr Jim Salinger, Honorary Research Fellow, University of Otago, comments:

“The standout events of the warm 2017 in New Zealand are the extreme events:

  • Floods especially in the North Island as a result of ex-Cyclone Debbie and ex-Cyclone Cook in the North Island in April, and the eastern South Island floods in July, and
  • The Marine Heatwave (MHW) starting in September and peaking so far in December, especially in the Tasman Sea and to the east of the South Island.

“The former, and other flooding events in the first seven months of 2017 meant it was the most expensive year so far costing $NZ242 million in insurance payouts. New Zealand is now ranked as ‘high hazard’ for these events by the Global Facility for Disaster Reduction and Recovery.

“The Marine Heatwave (MHW) had temperatures at least 3degC above average for several weeks. Impacts will be significant in the marine environment. There will be a movement towards more subtropical species of pelagic fish further south. Already snapper have been caught during December 2017 in Doubtful Sound, Fiordland which has never occurred before. And snapper have been spawning 3 months earlier than normal. Many other impacts are likely, such as changes in shellfish and seaweed around the coasts.

“Below is the January sea surface temperature anomaly forecast from the Bureau of Meteorology, which shows the MHW persisting throughout January, especially around the South Island. The early indications are that 2018 in New Zealand will be warmer than 2017, making it one of the warmest of years for a while.

“The MHW is expected to continue for the rest of summer.

“The Government has announced its intention of legislating the Zero Carbon Act with a Climate Commission – all very much needed moves.

“At the same time attention must also be focused on adaptation. The impacts of extreme weather in 2017 give us a taste of things to come in a warming climate.

“The report from the Ministry for the Environment released in December 2017 has warned that New Zealand lacks a coordinated plan to deal with future climate change, which threatens hundreds of billions of dollars of property and infrastructure. Actually, climate change is with us now!”

Lisa Murray, Senior Communications Meteorologist, MetService, comments:

“2017 has been a year of weather extremes. The people of New Zealand have had to deal with a relatively wet year until October with sodden soils, landslips and flooding, before ‘Mother Nature turned off the tap’ and we quickly went from wet to a very hot, dry end of year.

“A windy and cold January ran into a settled February, while March and April opened the door to deep lows causing sub-tropical deluges over the upper North Island producing record-breaking rainfall. May and June saw relatively settled weather while July through September there were continuous stormy low-pressure systems crossing New Zealand. This lead to a record wet January to September period for the Waikato and the greater Bay of Plenty region.

“At that point, Mother Nature tried to balance the books, with high pressure starting to reappear on the weather map during October. The intense high pressure stuck around during November and the first half of December. Extreme and persistent heat also prevailed under this long-winded high, but some areas experienced flash flooding after downpours/thunderstorms occurred, with estimate rain rates of between 40-50 mm/hr. During this period, several significant dry spell duration records fell and soil moisture levels in many places hit ‘severe deficit’ levels.

“In New Zealand, we get many extremes of weather. 2017 saw more than 173,000 lightning strikes recorded in New Zealand during the year, with numerous MetService Severe Weather Watches and Warnings Issued. So if you and your family are heading outdoors, whatever the time of year, it is important to keep up to date with the latest weather forecast and check for any official Severe weather information from MetService before you go.”

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