Feeling the heat: associations among daily ambient temperatures, extreme heat days and risk mortality in Australian dogs from New South Wales (1997–2017)

Global warming is expected to drive increases in daily temperatures and extreme heatwaves which are in turn expected to lead to increases in heat-related illness (HRI) morbidity and mortality in humans and animals, including dogs. The most severe form of HRI is heat stroke which is potentially fatal in dogs. The temperature range that increases the risk of mortality in dogs, and the impact of heatwaves, is not known. Twenty years of veterinary data from New South Wales (1997–2017) were analysed to explore potential associations between rates of mortality in dogs and both daily ambient maximum temperatures and extreme heat days. Extreme heat days were defined as any day that was over the 95th percentile (32°C) of daily maximum temperature in the study region across the study period. Results show that mortality increased as daily maximum temperature exceeded 25°C. There was a broadly linear increase of 0.6% (95% CI: 0.1% to 1%) in the risk of mortality for each 1°C increase in daily maximum temperature above 25°C. There was a 9.5% increased risk (95% CI: 4.3% to 15%) of mortality on extreme heat days compared with nonextreme heat days. Controlling for the effects of temperature, risk of mortality on public holidays increased 1.5 times (155%, 95% CI: 137% to 173%) compared with nonpublic holidays, and Sundays had nearly double the risk of mortality compared with all other days of the week. New Year's Day had the highest reported rate of mortality, followed by Christmas Day. This information should be used to inform veterinary public health policies in general and to inform key messaging about reducing the risk of death in dogs due to high ambient temperatures.