🇷🇪Réunion

Réunion is a French overseas department and island in the southwestern Indian Ocean (approximately 2,512 km²) located at 21°S, 800 km east of Madagascar. Dominated by two volcanic massifs — Piton des Neiges (3,070 m, an extinct volcano and the highest peak in the Indian Ocean) and the actively erupting Piton de la Fournaise (2,632 m, one of the world's most active volcanoes) — the island rises from tropical coastlines to alpine summits within 40 km.

This extreme topography creates dramatic climate zones: tropical humid (Af / Am) along the coastal lowlands with hot rainy summers and warm dry winters, subtropical highland (Cfb) in mid-elevation cirques and plateaus, and alpine tundra (ET) above 2,500 m on Piton des Neiges.

Réunion holds world rainfall records with Foc-Foc station recording 1,825 mm in 24 hours (7–8 January 1966), Cilaos recording 1,870 mm in 24 hours (15–16 March 1952) and 6,083 mm in 15 days during Cyclone Hyacinthe (1980), plus multiple other duration records recognized by the World Meteorological Organization.

Saint-Denis (capital, coastal) averages 23°C in July and 27°C in January with 1,600 mm rainfall concentrated November–April during the cyclone season. Saint-Pierre (southern coast) registers 21°C in July and 26°C in January with 800 mm — the drier leeward side. Cilaos (inland cirque, 1,200 m) records 13°C in July and 20°C in January with over 2,000 mm — a global rainfall extreme zone.

Le Port and Saint-Benoît average 23–24°C in July and 27–28°C in January with 900–3,000 mm depending on windward exposure. Piton des Neiges summit averages near 5°C in July with frequent frost and occasional snow. Réunion lies in the South Indian Ocean cyclone basin — severe events include Cyclone Hyacinthe (January 1980, 25 deaths, 6,083 mm rainfall at Commerson Crater in 15 days, severe floods and landslides), Cyclone Gamède (February 2007, over 5,000 mm in some areas, €300 million damage), Cyclone Belal (January 2024, major flooding and power outages, red alert issued), Cyclone Batsirai (February 2022, significant damage), recurrent coral bleaching in the lagoon reefs (2016, 2019–20, 2024 with up to 80% bleaching mortality in shallow zones), accelerating sea-level rise threatening Saint-Denis and coastal infrastructure (3.4 mm/year observed 1950–2020, projected 0.5–1.0 m by 2100), and increasing tropical cyclone intensity trends under warming ocean conditions.

Our archive covers 2 Réunion cities with daily ERA5 reanalysis data going back to 1940. The warmest July averages occur in Saint-Denis, around 23.6°C, while Saint-Denis records the coldest January nights near 24.8°C. Comparing the last decade against the 1940–1970 baseline, mean temperatures across these cities have risen by about 0.8°C.