A heatwave occurs when maximum and minimum temperatures are unusually high over a three-day period at a specific location. Heatwaves build up slowly and are considered the deadliest natural hazard in Australia.

Heatwave conditions

Under normal circumstances, heat builds up during the day and is discharged overnight. During a heatwave there is more excess heat during the day and less discharge of this heat overnight, resulting in increasing excess heat over time.

Heatwaves put pressure on people’s health, emergency and essential services like power and water.

Two-panel diagram comparing temperature patterns over four days to illustrate the difference between “not a heatwave” and a “heatwave,” relative to a heatwave threshold (local mean temperature 95th percentile, shown as a horizontal line at 0°C). The verti

Source: MacClune, K., Rubenstein, N., Norton, R., Pestalozzi, A., Keating, A., 2026

Recent event: November 2025

  • A severe to extreme heatwave occurred across the Northern Rivers and lasted for 6 consecutive days.
  • Grafton reached 38°C, Casino 37°C and Lismore 36°C.
  • Health services reported increased demand for medical assistance and heat-related illness presentations.

Current and future risk

Heatwave intensity in the Northern Rivers

Heatwave intensity is measured using an excess heat factor (EHF) index – which measures how much of a shock to the body the forecast temperature will be. This index measures modelling for heatwave across NSW. The map below shows the Northern Rivers having the highest EHF in NSW.

Map of New South Wales, Australia, showing expected annual heatwave severity using the Excessive Heat Factor Severity (EHFSEV) at present day. Colours range from light beige (lower severity, around 2) to dark red (very high severity, up to about 3.9), wit

Data source: NARCliM2.0 climate data, post-processed by Taylor Fry/Risk Frontiers

Heatwave intensity over time

Four side-by-side maps showing projected changes in heatwave severity for the Northern Rivers region (including Kyogle, Tweed, Byron, Ballina, Lismore, Richmond Valley and Clarence Valley) at present time and three future periods. The maps use the same co

Data source: NARCliM2.0 climate data, post-processed by Taylor Fry/Risk Frontiers

Current risk

  • The Northern Rivers has the highest heatwave intensity of any region in NSW.
  • There is a 17% chance of an extreme heatwave in the Northern Rivers in any given year.
  • Heatwaves can happen anywhere in the Northern Rivers.
  • Towns and built up areas also get hotter because concrete and buildings hold onto heat.
  • They usually occur in summer, but can happen at other times when very hot, still weather settles over the region.

Future risk

  • Over time, heatwave risk in the Northern Rivers will increase as a result of climate change and population growth.
  • Heatwave intensity is expected to increase from present day severe heatwaves, to extreme heatwaves by the end of the century.
  • By 2090, the annual likelihood of an extreme heatwave is projected to increase to around 45% (from 17% currently).

Impacts

Built

  • Damage to transport and electrical infrastructure
  • Strain on energy and water systems
  • Intensified urban heat island effects

Social

  • Death and heat related illness
  • Mental and physical distress
  • Disruptions to daily life

Economic

  • Reduced productivity for outdoor and indoor workers
  • Losses to crops and livestock

Natural

  • Degraded air quality
  • Increased drought and bush fire risk
  • Injury or death to wildlife sensitive to
    extreme heat


Next steps

Note: The information contained on these Have Your Say website pages is general information only, based on knowledge and understanding at the time of publication (June 2026) or otherwise based on data which pre-dates its publication, and may be subject to change at any time without notice. The State of NSW and its agencies (including the NSW Reconstruction Authority) do not give any warranty or representation as to the accuracy, reliability or completeness of the information. Read our full legal notice at bottom of the Have Your Say landing page.