Where heat does not come in waves: a framework for understanding and managing chronic heat

This study argues that heat research and practice have focused too narrowly on heat waves as acute, episodic emergencies, obscuring the chronic exposure of billions of people — predominantly in the global tropics and subtropics — to dangerous levels of heat for months at a time. The authors propose "chronic heat" as an alternative framing, defining it as a dangerous heat hazard that persists for several months of the year, operationalized as locations where the daily maximum heat index exceeds 90°F (32.2°C) for more than 90 days (the equivalent of a season). They note that under the World Meteorological Organization's heat-wave definition, the tropics and subtropics register very few events, or none, despite enduring dangerous heat indices for much of the year — a paradox illustrated by contrasting an acute-heat city (Portland, Oregon) with a chronic-heat one (Miami, Florida). Drawing on Simpson et al.'s framework for complex climate risk, the paper reconceptualizes vulnerability, exposure, risk, and adaptive capacity for chronic rather than acute conditions, structuring its argument around how temporal factors differentiate the hazard, how individual and societal drivers create cumulative and intersectional risk, what adaptive responses are needed, and what a research agenda should prioritize.

The findings reveal that chronic heat poses distinct risks because exposure accumulates seasonally and annually across multiple spaces — home, work, commuting, and recreation — and intersects with enduring vulnerabilities such as age, health, housing quality, livelihood, and economic insecurity, compounded at the hyperlocal scale by the urban heat island effect (one Miami-Dade study found maximum heat index values 11°F higher across the metro region than at the airport station). Unlike acute heat, which brings relief once a wave dissipates, chronic heat offers no consistent respite, eroding "resilience reserves," pushing people toward acclimatization and adaptation limits, and producing under-documented outcomes like kidney disease among agricultural workers alongside quality-of-life, financial, and social harms. Because chronic heat is rooted in systemic inequalities, the authors argue that responses must move beyond reactive emergency management toward ongoing, structurally-oriented solutions — favoring technical/infrastructural, institutional, and nature-based adaptations over individual behavioral ones, redefining climatological thresholds around heat seasons rather than discrete events (as the City of Phoenix does), and mobilizing social services, multi-level governance, adaptation champions like Chief Heat Officers, and non-traditional actors such as utilities and landlords. They close with a six-priority research agenda — better data sharing, granular hyperlocal data, revised metrics and thresholds, long-term heat–health surveillance, qualitative methods, and transdisciplinary collaboration (illustrated through a Miami-Dade network map) — concluding that chronic heat, while pervasive and intensifying under climate change, is also an opportunity to address systemic inequities and improve living standards for the most vulnerable.