Predictions of heat extremes on multi-week to seasonal timescales

Research objective

Investigate the ability, or skill, of POAMA for providing forecasts of extreme heat over Australia on multi-week to seasonal forecast time scales.

Project duration

2011 – 2014

Outcomes

The first part of the project was to understand how large-scale climate drivers can lead to episodes of extreme heat over Australia:

Researchers then examined the ability of POAMA to capture the relationships between climate drivers and extreme heat that Australia has experienced in the past.

The second part of the project directly assessed POAMA’s forecasts for extreme heat, compared with what was observed.

POAMA’s forecasts are not equally skilful at all times of the year, places, lead-times and forecast periods. For example, POAMA tends to be more skilful for forecasts over eastern than western Australia, and tends to have good skill during spring months. It has less skill during summer months.

Beyond very short-term forecasts, there is more skill for forecasting an extreme season than for forecasting an extreme month.

In the third part of the project, researchers developed POAMA experimental forecasts which focus on forecasting extreme heat in the upcoming weeks, fortnights, months and seasons:

  • Extreme Heat Days Forecast for Australia: the number of hot days within the upcoming months or season, and chance of having more than the usual number of hot days. (A ‘hot day’ means the maximum temperature is over 90% of historical observations for time of year and region.)
  • Extreme Temperature Forecasts: the chance that the upcoming weeks, fortnights, months or season will be in the top decile (10% or decile 10) or top quintile (20% or decile 9 or 10) of usual events.
  • Rainfall and Temperature Histograms: daily rainfall or temperature over a selected period of time, for whichever region you select.
  • Heatwave Forecast for Australia: the chance and location of low-intensity, severe and extreme heatwaves for any time up to 1 month out. (A ‘heatwave’ is 3 or more days of high maximum and minimum temperatures.)
  • Sub-tropical Ridge High over Tasman Sea (STRH) Index Forecasts: the state of the ridge over the Tasman Sea (read more about the Sub-tropical ridge), which has a strong influence on the chance of extreme heat over southern Australia.

The most important result of the project is to understand POAMA’s skill for predicting heat extremes. Multi-week predictions of heat extremes are very important to agriculture for scheduling, planning and risk management: from managing irrigation demand to planning sowing, harvesting and more.

Researchers also detail recommendations for forecasting and forecast products.

Read the plain English summary of the project.

Research contact

Dr Debbie Hudson

Bureau of Meteorology

D.Hudson@bom.gov.au

Phone: 03 9669 4796

Sub-tropical Ridge High over Tasman Sea

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