Rainfall Records Shattered In Auckland, New Zealand

New Zealand’s official weather agency, MetService, posted some stunning facts in the past few days. One Tweet by the agency noted that the Auckland Airport had broken its record for wettest 24-hour period with 249 mm. For those of us in the United States that do not think in metric units, that is just under 10 inches of rainfall. Here are some the numbers and perspectives on the extreme January rainfall in New Zealand as well as some bigger picture implications for all of us.

The MetService also noted that the daily total is not the only historic aspect of this rainfall event. They tweeted, “Not only that but Auckland Airport got its average monthly rain for January in less than hour today. It looks like it will be the wettest month on record for Auckland never mind the wettest January on record.” The wettest January (remember it is Summer there right now) in Auckland was 1986 (20 cm or 7.87 inches). The wettest month on record is July 1998 (30 cm or 11.81 inches). January 2023 has already produced 32 cm (12.59) inches of rainfall at the time of writing. There are still a few days left in the month and more rain is in the forecast.

The most provocative Tweet that I saw provides great perspective on this rainfall total using a baseball analogy. Jonathan Erdman is a senior meteorologist with The Weather Company. His Tweet below frames the record rainfall at Auckland Airport in terms of home runs by New York Yankees slugger Aaron Judge. To achieve a similar record-breaking margin, Aaron Judge would need to hit 95 homeruns in 2023. He hit an astounding 62 in 2022.

Yes, this is an extreme weather event, but it smells of what many of us have warned about as climate changes. Basic physics tells us that a warming atmosphere increases the capacity of available water vapor. Climate scientists have “cried in the wilderness” for decades about higher intensity rainfall events in response to atmospheric warming. The 2018 U.S. National Climate Assessment report wrote, “The frequency and intensity of heavy precipitation events across the United States have increased more than average precipitation and are expected to continue to increase over the coming century….”

Ben Noll is a meteorologist at the National Institute of Water and Atmospheric Research in New Zealand. He provides important perspective on the root causes of the extreme rainfall in Auckland. Guess what? Noll discusses the natural and anthropogenic climate change context for the event. He tweeted, “What drove Auckland’s deluge?” He then laid out the following list:

1. La Niña (colder than normal eastern equatorial Pacific waters that lead to teleconnections modifying atmospheric patterns).
2. Precipitable water (PW or PWAT) values above the 90th percentile (PW is a measure of water vapor in the atmospheric column).
3. Saturation in the atmospheric column.
4. A low level jet, convergence and resulting convection.
5. A marine heatwave (a prolonged existence of abnormally warm ocean water).

However, he ended the Tweet with this statement – “All on the backdrop of a warming climate.” This is an important reminder that gets lost in the narrative. It’s “and” not “or.”