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AUCKLAND JANUARY 2023 RAINFALL EVENT ANALYSIS

OVERVIEW

This project involves analysing Auckland, New Zealand's rainfall data from January 2023, a period marked by an exceptional La Niña event, and comparing it to historical January averages spanning from 1962 to 2023. This comparison aims to illustrate the impact of climate patterns, such as La Niña, on regional weather. By examining over 60 years of data, I will identify trends, anomalies, and the extent of deviation from the norm in 2023's rainfall. This analysis will provide insights into climate variability and help understand the implications of changing weather patterns in Auckland, particularly in the context of climate change.

INTRODUCTION

In January 2023, Auckland, New Zealand, was significantly impacted by a La Niña event, which led to unprecedented rainfall and extreme weather conditions. La Niña, a phase of the El Niño-Southern Oscillation, is characterised by cooler-than-average sea surface temperatures in the central Pacific Ocean, influencing global weather patterns. This particular event was compounded by the positive phase of the Southern Annular Mode, resulting in higher-than-normal air pressure over New Zealand.

The impact in Auckland was profound. The city, home to 1.6 million people, experienced its wettest day on record on January 27th, with an estimated 240 millimetres (9.8 inches) of rain, equivalent to a typical summer's total rainfall, falling in a single day. This extreme downpour led to widespread flooding, infrastructure damage, and multiple landslides. Over the month, Auckland recorded around 32 cm (12.59 inches) of rainfall, far exceeding typical January averages.

The heavy rains were attributed to an atmospheric river event, a narrow corridor of concentrated moisture in the atmosphere, which brought relentless maritime heatwave conditions to the upper North Island.

The aftermath of the La Niña event posed significant challenges for Auckland, disrupting lives and hindering recovery efforts.

TYPICAL WEATHER AND RAINFALL PATTERNS IN AUCKLAND, NEW ZEALAND

Geographic Influences

Auckland, located on the North Island of New Zealand, experiences typical weather and rainfall patterns influenced by its unique geography. Its position between the Tasman Sea and the Pacific Ocean exposes the city to maritime air masses, resulting in mild temperatures and relatively high humidity. The presence of mountain ranges, such as the Waitakere Ranges, causes orographic uplift, leading to increased rainfall on the windward side. Auckland's temperate maritime climate is characterized by mild winters, warm summers, and moderate rainfall throughout the year, influenced by its coastal location and surrounding topography.

Rainfall during Seasons in Auckland, New Zealand

The maximum seasonal rainfall line (red) shows a decrease from summer to autumn, a sharp increase in winter, followed by a decrease in spring. The minimum seasonal rainfall (orange) gradually increases from summer to spring with a slight dip in winter. The average rainfall (green) peaks in winter, suggesting this is the wettest season overall. The standard deviation (purple) remains relatively constant across the seasons, indicating a consistent variability in rainfall amounts. 

Overall, the data suggests a seasonal pattern with the highest rainfall in winter (June - August), and significant variability between the maximum and minimum rainfall figures, which could be indicative of occasional extreme weather events or differing microclimates within the region studied.

​LA NIÑA RAINFALL EVENT IN AUCKLAND, NEW ZEALAND JANUARY 2023

The January 2023 rainfall event in Auckland, driven by La Niña, differed starkly from normal patterns. Typically, Auckland experiences moderate rainfall in January. However, this event brought about 240 millimetres of rain in a single day, equivalent to a full summer's worth, marking it as Auckland's wettest day ever. Such extreme rainfall led to unprecedented flooding and landslides, unlike the usual, more manageable January rains. This deviation from the norm is indicative of the heightened extremes in weather patterns, likely exacerbated by climate change, showcasing a shift towards more unpredictable and severe meteorological events.

La Niña is a climatic phenomenon characterized by cooler-than-average sea surface temperatures in the central and eastern Pacific Oceans. It influences global weather patterns, often resulting in wetter conditions in some regions and drier in others, and is part of the El Niño-Southern Oscillation climate pattern.

Monthly Sea Surface Temperatures (La Nina).gif

January 2023 Rainfall Event Return Period

Return Period

A return period refers to the statistical likelihood of an event of similar magnitude occurring. For instance, if this January 2023 event is described as having a 100-year return period, it suggests that on average, an event of this magnitude is statistically expected to occur once every 100 years.

The above-displayed bar chart provides the estimated return period, calculated using the Gumbel distribution, for extreme weather events in Auckland, New Zealand, spanning from 1962 to 2023. The vertical axis represents the return period in years, while the horizontal axis denotes the year of occurrence. The return period is calculated using the Gumbel distribution, a statistical model commonly utilized for predicting the occurrence of extreme events.

In most years, extreme weather events in Auckland occur with an average frequency such that a similar event is statistically expected to happen once every ten years or less.

However, the data point for 2023 deviates significantly from the rest, suggesting an event of unprecedented magnitude, with a return period exceeding 60 years.

January (1963 - 2022) vs. January 2023uary

When examining the rainfall from the La Niña event in January 2023 against the historical January averages in Auckland, it becomes evident how exceptional the 2023 rainfall was.

The above graph shows a stark contrast between January 2023's rainfall in Auckland and historical data spanning from 1963 to 2022. The blue line, representing 2023, displays a significant anomaly in the maximum one-day rainfall, soaring above the historical average, indicative of the exceptional rainfall event, attributed to La Niña. This singular spike suggests an unusual weather occurrence, diverging markedly from the established pattern over the past 60 years. Despite this, the average one-day rainfall in 2023 sits lower than the long-term average, hinting at fewer rain days but with more intense precipitation when it occurs. The Intense rainfall over a brief period, adds to the dangers of this rainfall event.

The combination of these factors underscores the exceptional nature of Auckland's January 2023 rainfall.

CONCLUSION

In conclusion, the January 2023 La Niña event in Auckland, New Zealand, represents a significant deviation from the city's typical weather patterns, characterised by an extraordinary rainfall event. This anomaly, with a return period exceeding 60 years, underscores the increasing unpredictability and severity of weather events, likely influenced by climate change. The unprecedented rainfall challenged Auckland's infrastructure and resilience, highlighting the necessity for enhanced preparedness and adaptive strategies in urban planning and disaster management. This event serves as a stark reminder of our environment's dynamic nature and the vastness and power of our planet.

 

REFERENCES

  1. National Institute of Water and Atmospheric Research (NIWA). (2023). "CliFlo: The National Climate Database." Retrieved from https://cliflo.niwa.co.nz/pls/niwp/wgenf.genform1.

  2. NIWA Climate. (2023). "Climate Summary for January 2023." Retrieved from https://niwa.co.nz/climate/monthly/climate-summary-for-january-2023.

  3. Shepherd, M. (2023, January 27). "Rainfall Records Shattered in Auckland, New Zealand—It Wasn't Even Close." Forbes. Retrieved from https://www.forbes.com/sites/marshallshepherd/2023/01/27/rainfall-records-shattered-in-auckland-new-zealandit-wasnt-even-close.

  4. Wikipedia Contributors. (2023). "2023 Auckland Anniversary Weekend floods." Wikipedia. Retrieved from https://en.wikipedia.org/wiki/2023_Auckland_Anniversary_Weekend_floods.

  5. Petley, D. (2023, January 30). "Auckland 1." The Landslide Blog, American Geophysical Union. Retrieved from https://blogs.agu.org/landslideblog/2023/01/30/auckland-1.

  6. Center for Disaster Philanthropy. (2023). "2023 New Zealand Floods." Retrieved from https://disasterphilanthropy.org/disasters/2023-new-zealand-floods.

  7. NOAA PMEL. (n.d.). "What is La Niña?" Retrieved from https://www.pmel.noaa.gov/elnino/what-is-la-nina.

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