<p>In the summer of 2022, our team of climatologists and researchers piloted the first heat warning system that ranks heat events based upon human health outcomes. This system uses local all-cause mortality data in addition to meteorological factors including air mass identification and the Excess Heat Factor to identify heat events that are likely to endanger human health in the region and applies three categories representing increasing severity. In this study, we evaluated this system by comparing the heat events it identified in Seville, Spain between 1995 and 2022 with those identified by the Spanish national meteorology agency (AEMET). We also compared the outputs from both systems against all-cause mortality data over the same time period. We found that our system captured more dangerous heat events than the meteorology-only criteria of AEMET and that the majority of identified heat events occurred during periods of elevated mortality. Additionally, the agreement between systems differed by event severity; roughly half of the high mortality “Category 3” events identified by our system were also identified by AEMET, but AEMET only issued alerts during one of the 24 more minor “Category 1” events that our system identified, even though these events were also correlated with increased mortality. Overall, these results show the potential of health-based warning systems in identifying dangerous events that might be missed by traditional meteorology-based systems.</p>