Relative change in decile value of ambulance callouts between baseline (summer nonhot days) and hot days in Brisbane (based on 1/7/2003–4/8/2011 data). Blank (white) POA indicates that there was no difference in ambulance callout decile value, whereas yellow and orange POA indicate a lower ambulance callout decile value on hot days as compared with summer nonhot days. Red indicates an increase in demand for ambulance services on hot days.