Tracking Australia's climate: 2014 and the severe weather season

Issued

Looking ahead to the severe weather season

The arrival of spring and summer in Australia heralds the approach of hot weather, Christmas, school holidays and, for many, the beach.

However, in terms of climate, spring and summer are also the most significant periods of the year for Australia, since they are associated with the bushfire and tropical cyclone seasons, heatwaves, more frequent severe thunderstorms (with their inherent risk of hail, lightning and flash flooding), and northern monsoon.

The occurrence and impact of major fires and floods are influenced by the lead-in climate conditions, also known as the antecedent conditions. For example, a prolonged period of unusually warm and dry conditions across autumn and winter can lead to an early and severe start to the fire season — as occurred in spring and summer 2008/2009 and 2013/2014. Similarly, a prolonged period of rainfall prior to the onset of the northern wet season leads to saturated soils and sometimes flooding when the monsoon arrives — as occurred in 2010/2011 and 2011/2012.

Year-to-date climate conditions for Australia become meaningful toward the end of the calendar year. Climate monitoring and prediction is an important input to decision-making and planning for the summer severe weather season in Australia.

This type of climate information is also of interest to businesses and communities beyond those working in emergency management. For example, an unusually warm year will likely see increased use of electricity for cooling, while irrigators and households alike may use more water on crops and gardens. The retail sector will see consumers purchasing summer attire earlier in spring and later in autumn.

How is our climate tracking in 2014?

The national mean temperature in September 2014 was more than 1 °C above average, while October saw temperatures of 1.91 °C above average. The year-to-date and the 12-month running mean temperature ending in October 2014 are the 5th- and 6th-highest on record (+0.82 °C and +0.77 °C, respectively). This continues a spell of high temperatures since 2013, following two relatively cooler ('near normal') years in 2011 and 2012 that were influenced by twin La Niña events in the Pacific.

Figure 1. Australian area-averaged monthly mean temperature anomalies for the period January 2011 to October 2014. Anomalies are calculated against the 1961-1990 average.

Figure 1. Australian area-averaged monthly mean temperature anomalies for the period January 2011 to October 2014. Anomalies are calculated against the 1961–1990 average.

How might the year end?

Firstly, we consider the November and December monthly Climate outlooks, combined with a 50% chance of an El Niño occurring; both of these favour continued above-average temperatures (relative to 1961–1990) over the coming months. These data suggest that the remainder of the year is likely to see a temperature anomaly in the range of +0.5 to +1.0 °C, though higher or lower temperatures cannot be ruled out.

Secondly, we look at outcomes based on historical scenarios. Initially we consider the middle value from the full climate record (1910–2013) for the November to December period (an anomaly of −0.08 °C). This has 52 years with the November to December mean temperature anomaly both lower and higher than −0.08 °C, and results in an annual temperature anomaly for 2014 of +0.67 °C; the seventh-warmest year on record.

Possible November to December mean temperature anomalies (relative to 1961–1990) and the consequent 2014 annual anomaly and rank for Australia.
  November to December anomaly (°C) Projected annual anomaly (°C) Historical rank
Warmest November to December on record (occurred in 1990) +1.40 +0.92 3
Persistence of January to October 2014 anomaly +0.82 +0.82 4
Average anomaly since 2000 +0.42 +0.75 5
1981–2010 November to December average +0.17 +0.71 5
The Bureau’s dynamical model forecast for November to December 2014 +0.80 +0.81 = 4
Coldest November to December on record (occurred in 1916) −2.05 +0.34 16

Scenarios based on recent climate averages may be more realistic for predicting the likely 2014 annual mean. Using the average temperature anomaly for November to December over either the 19812010 30-year climate reference period or the November to December average since 2000 would result in the fifth-warmest year on record.

Taking the coldest and warmest November to December periods from the entire historical record results in a 2014 annual mean temperature anomaly of +0.34 °C and +0.92 °C, respectively. A persistence of the anomaly for the year so far, for the period January to October 2014, would result in +0.82 °C, the fourth-warmest year on record.

Figure 2. The historical distribution of Australian mean annual temperatures, compared to the distribution of possible 2014 temperatures, calculated using the full historical range (1910–2013) for the November–December period. This highlights that is it virtually certain that the year will end with a well above average temperature.

Figure 2. The historical distribution of Australian mean annual temperatures, compared to the distribution of possible 2014 temperatures, calculated using the full historical range (1910–2013) for the November to December period. This highlights that is it virtually certain that the year will end with a well above average temperature.

These scenarios suggest that while 2014 is likely to fall short of the record-breaking annual mean temperature anomaly of +1.2 °C set in 2013, and the most likely outcome for Australia is for a temperature in the warmest five years on record.

Taking a longer view, virtually all scenarios suggest that the two years 2013 to 2014 will be the warmest two-year period in Australia’s recorded history.

Which areas are in drought?

Much of Australia has been dry since April 2014, particularly across parts of southern Western Australia, southern and central western Queensland, northeastern New South Wales, parts of western Victoria and south eastern South Australia and most of Tasmania. Prolonged drought conditions have affected inland Queensland for the past two years.

In the past four months, rainfall has been significantly below average across most of Victoria and South Australia, southern inland New South Wales, southeast Queensland and parts of western Western Australia. This has resulted in short-term drought conditions emerging in western Victoria and adjacent areas across the border in South Australia and the Riverina. These regions are very fire prone during the summer months.

How have global temperatures been tracking?

The US National Oceanic and Atmospheric Administration (NOAA) has reported that the January to September temperatures in 2014 are currently tied with 1998 as the warmest on record (the global records begin in 1880). September 2014 was the warmest September on record globally and the prior months of August, June and May 2014 were also the warmest months recorded globally according to NOAA. The warmth has been largely driven by sea-surface temperatures, which were the warmest on record.

A continuation of the January to September anomalies would lead to 2014 being in the top three warmest years on record globally. With current significant levels of warmth in the oceans, and the likelihood of persisting warmer-than-average conditions in the Pacific, there is a strong possibility that 2014 will be the warmest year on record.

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