1997-98: The El Niño of the Century, Watched From Start to Finish

In the spring of 1997, the instruments strung across the equatorial Pacific began reporting something extraordinary. Warm water was surging eastward with unprecedented speed; sea levels were rising; the trade winds were faltering. This time, unlike in 1982, science was watching. The buoys of the TAO array streamed their readings home by satellite, the TOPEX/Poseidon altimeter mapped the swelling ocean from orbit, and forecast models began issuing a consistent, alarming message months in advance: a monster was coming.

It arrived on schedule. By November 1997 the Oceanic Niño Index reached +2.4 — the strongest El Niño of the 20th century, quickly dubbed "the El Niño of the century."

A world remade for a year

The event's fingerprints appeared on every continent. Peru and Ecuador, El Niño's oldest victims, suffered devastating floods and mudslides. In China, the Yangtze floods of 1998 — often attributed in part to the event — killed more than 3,000 people. Indonesia endured deep drought, and vast forest and peat fires in 1997 wrapped Southeast Asia in a choking, region-wide haze. In East Africa the pattern inverted: Kenya and the Horn were deluged, and the floods seeded an outbreak of Rift Valley fever. India's monsoon came in weak. California and the Gulf states were raked by record winter storms; Changnon's accounting put US losses at around $4.2-4.5 billion, partly offset — in a characteristic El Niño irony — by savings from an unusually mild northern winter.

The oceans suffered a slower catastrophe. In 1998, warm water triggered the first global mass coral bleaching event ever recorded. By the time it ended, roughly 16 percent of the world's coral reefs had been lost — an opening chapter in a story that later events, notably the Godzilla El Niño of 2015-16, would continue.

The human accounting was grim. United Nations and UNEP figures put the global death toll at roughly 23,000-24,000. UNEP reported the event "cost governments up to $45 billion"; damage figures of $32-45 billion are commonly cited, and estimates across studies range as high as $96 billion.

The first El Niño seen whole

Yet 1997-98 occupies a paradoxical place in history: the most destructive El Niño of its century was also science's greatest triumph over the phenomenon to date. It was the first event observed from beginning to end.

The infrastructure built after the 1982-83 debacle performed exactly as designed. The TAO array — roughly seventy moored buoys completed across the equatorial Pacific in December 1994 — recorded the subsurface heat buildup and the westerly wind bursts that launched the event. Overhead, the TOPEX/Poseidon satellite, measuring sea-surface height to a few centimetres, tracked the warm water's advance in a way no ship or buoy line could. At the event's height, sea levels ran 14-32 cm above normal across a vast tongue of the eastern Pacific.

From that altimetry came the images that made this El Niño a household name: the false-color maps of 23 October and 1 November 1997, showing a great white-and-red blade of elevated, overheated water stretching along the equator toward the Americas. Published everywhere, they gave the public something no previous El Niño had: a portrait.

Forecasts put to work

Most consequentially, the models worked. Coupled forecast systems — descendants of the pioneering Cane-Zebiak model — flagged the developing event months ahead, and for the first time governments acted on an El Niño forecast at scale. Peru and other exposed countries mounted preparedness campaigns: reinforcing infrastructure, pre-positioning relief, adjusting agricultural plans. California braced for its storm season in advance.

The toll was still enormous — forecasts cannot empty a floodplain of its people or fireproof a drought-stricken forest. But 1997-98 established the template that has governed every event since: detection by the observing system, months of model-based warning, coordinated national preparedness. The full chain of institutions behind that template, from TOGA to today's monthly outlooks, is traced in our history of ENSO forecasting.

The benchmark event

For a generation, 1997-98 was the universal reference point — the event against which every subsequent warming was measured, the source of the imagery, the case study in a thousand papers. When forecasters in 2015 and again in 2023 reached for comparisons, they reached first for 1997.

Its dual legacy endures. As a disaster, it demonstrated El Niño's full destructive range in the modern, interconnected world — tens of thousands dead, tens of billions lost, ecosystems from the Yangtze basin to the coral reefs transformed. As a scientific milestone, it proved that the phenomenon Peruvian fishermen had named a century earlier could be watched, understood and anticipated from its first stirrings to its last. No El Niño before it was seen whole; every El Niño since has been.