Tropical nights, defined as nights when temperatures do not fall below 20°C, are occurring more often in recent summers and pose growing health and comfort challenges in many regions.
Definition and observed trends
A tropical night is counted when the daily minimum temperature remains above 20°C. Meteorological services have recorded a rising number of these nights in regions that historically had few, making them a useful indicator of changing climate patterns.
Regional evidence of increases
Studies focusing on Iberian and Portuguese cities show a clear trend: coastal and lower‑latitude urban areas have seen significant increases in the frequency and persistence of hot nights, with methods that identify nights likely to cause heat stress becoming more widely used for local planning and public‑health assessment.
Long‑term analysis and drivers
Research across Spain and neighbouring regions using multi‑decade temperature records finds upward trends in minimum temperatures consistent with global warming, with the number of tropical nights rising substantially since the late 20th century and accelerating in recent decades.
Urban amplification and impacts
Urban heat islands magnify warm‑night conditions because built surfaces store daytime heat and release it overnight, prolonging elevated temperatures. Climate indicators and adaptation tools highlight tropical nights as a key metric for heat‑health planning.
Health and wellbeing
Tropical nights reduce overnight cooling that people rely on to recover from daytime heat, worsening sleep quality and increasing heat‑related health risks, particularly for vulnerable groups in densely populated cities, as reported in recent public‑facing analyses of heat and sleep trends.