Heatwave characterization in Chile according to the Excess Heat Factor (1979–2018)

Heatwaves (HW) are among the most impactful climate-related hazards, with increasing consequences for human health, ecosystems, and infrastructure under ongoing global warming. Despite growing attention worldwide, their characterization in South America remains limited, particularly from a biometeorological perspective. This study aims to characterize heatwave intensity, frequency, duration, and spatial extent in continental Chile using the excess heat factor (EHF) index, and to identify the synoptic conditions associated with representative extreme events. We apply the EHF index to high-resolution gridded temperature data covering the period 1979–2018 and analyze its components to assess multiple dimensions of HW behavior. In addition, we evaluate temporal trends and perform a synoptic characterization of three representative events in northern (Arica), central (Santiago), and southern (Puerto Montt) Chile. The results reveal a marked geographic contrast in HW dynamics: central Chile exhibits the highest intensity and recurrence, northern Chile shows longer and more variable events, and southern Chile, although historically less affected, is increasingly exposed. Significant positive trends are observed in HW intensity, duration, and spatial extent, with a notable expansion of affected areas after 2000, when median national HW coverage frequently exceeds 40–60% of continental Chile. Synoptic analyses indicate a consistent presence of mid-tropospheric ridges and persistent surface anticyclones, favoring subsidence and limiting atmospheric cooling. These findings highlight the increasing relevance of HW as a climate hazard in Chile and demonstrate the suitability of the EHF index for identifying events with potential health impacts. The results provide a basis for improving early warning systems and supporting region-specific climate adaptation and risk management strategies.