El Niño has been observed for centuries - starting with Peruvian fishermen who noticed that in certain years the ocean was warmer, and brought more tropical fish to their nets.But it's only been in recent decades that live monitoring of ocean and atmosphere conditions has allowed forecasters to observe the climate phenomenon develop in real time.Climate Prescience director and scientist Nathaneal Melia says the El Niño-Southern Oscillation is the largest form of natural climate variability in the globe."It's absolutely huge for the Pacific region."But New Zealand sits thousands of kilometres away from the high-impact zone in the tropical Pacific, and so El Niño's effects are weaker and less predictable here than somewhere like Indonesia, which almost always suffers through wildfire and drought.Melia likens El Niño to Zeus, with other climate drivers acting as minor and demi-gods in a "pantheon" of influences on New Zealand's weather."We rely on El Niño's effects being translated down through these other sorts of atmospheric phenomena and oscillations... and even those can sit a bit away from us. They send these messages to us through these whispers."University of Waikato climate scientist Luke Harrington says New Zealanders "like to get pretty excited any time an El Niño event is declared".That's often misplaced, he says. "We've actually got a quite weak relationship [with it]."University of Waikato climate scientist Luke HarringtonSUPPLIEDModern observations show there are certain trends that are more likely, though, when a strong El Niño is in force.The coming El Niño is likely to rival or exceed previous strong El Niño events - here's how the big ones have played out here.1982-83Back in 1982, James Renwick was a young MetService researcher when the agency issued its first-ever press release about a coming El Niño that spring and summer.Now a professor of physical geography at Victoria University and former climate commissioner, Renwick was part of the group who produced the climate outlook, based on new research."It turned out to be almost exactly right, which was pleasing - I can't say that's worked every time since, but it did then."What New Zealand experienced over the summer of 1982 and 1983 were "textbook" El Niño conditions, he said: drier than normal conditions in the east, wetter than normal conditions in the west, and a westerly flow that generally kept temperatures cool."It was a big deal," Renwick says."I remember the farming community were struggling - it even featured in Footrot Flats."Droughts were declared in Hawke's Bay and Gisborne, and El Niño loomed large in the media and public mind for months.1991-1994Contrary to popular belief that El Niño means a hot summer, it actually often brings cooler temperatures with it thanks to prevailing sou'westers, Renwick says.The El Niño events of the early 1990s weren't especially strong, but they came back-to-back and also coincided with the 1991 eruption of Mount Pinatubo in the Philippines, creating a "canopy" of volcanic debris in the atmosphere.Summer rainfall patterns in New Zealand during five modern El Niño events.Supplied / ESNZ"That cooled the whole planet for a couple of years - 1992, 93," Renwisk says."That added up to 1992 having the coldest winter for 40-odd years or so."When temperatures are lower, there's less moisture in the air, so less rain falls - putting pressure on farming, water supplies, and the hydro lakes. As well as being freezing, the winter of 1992 therefore also coincided with a power crisis in New Zealand, as El Niño exacerbated the prolonged drought.Two years later, in winter 1994, a third El Niño event in a row was blamed for the Auckland water crisis.Earth Sciences New Zealand principal scientist Chris Brandolino says El Niño can still bring "spiky" temperatures with it.The hottest temperature ever recorded in New Zealand was 42.4°C at Rangiora on 7 February, 1973 - in the middle of another major El Niño event.It's a record that's stood for more than 50 years - with the twin influences of climate change and El Niño, could it fall this summer?1997-1998Likie 1982-83, the way El Niño played out over the summer of 1997-98 was "textbook" for New Zealand, Renwick says.A government report published in mid-1998 noted that eastern regions were "badly affected" by drought."The most extreme conditions [were] evident in Marlborough, North Canterbury and parts of the Wairarapa and Hawke's Bay."Apple-growers found their burgeoning crops got sunburnt and overheated, leading some orchardists to leave nearly half the fruit unpicked.The report estimated the costs to agriculture alone were $425 million (about double that in today's money).Atypical hot temperatures towards the end of the summer put pressure on city populations, too."Higher air temperatures, by as much as 3°C above average, have led to a heavier demand for urban air-conditioning and hence for electricity," the report noted.However, there was no repetition of the 1992 electricity crisis that occurred during the 1991-94 El Niño.Globally, the 1997-98 El Niño hit hard, it said."Reported impacts include drought-induced food shortages, massive forest fires, thousands of deaths from starvation, flooding and diseases, and reductions in economic growth forecasts."2015-2016The most recent strong El Niño was forecast to be much more severe than what eventually transpired, Luke Harrington says."That was also supposed to be a super El Niño. It was pretty warm, and there probably were some regional impacts in some places, but it wasn't very widespread or significant."Earth Sciences New Zealand says typical south-westerly patterns developed at first, in December 2015."[But] a change to more northerly-quarter winds than usual for January and February brought more rain and alleviated fears of El Niño-associated drought in many parts of the country."University of Waikato climate scientist Luke Harrington says the worst drought that New Zealand has reliable observations for occurred during 1914-15, which also coincided with an El Niño,However, he says it's important to note that not every El Niño brings drought to New Zealand - and not every drought happens in an El Niño year."Some of our largest [drought] events of the recent past haven't occurred during El Niño events - I'm thinking particularly 2012-2013, the 2007-08 Waikato droughts, the same with 1988-89 as well."Earth Sciences, in its summary of the 2015-16 El Niño, noted that drought on the east coast "is not a certainty during every El Niño".'[However], the risk of El Niño-driven drought during a strong event is enough to warrant risk-management actions by farmers and others whose livelihoods are likely to be adversely affected by prolonged dry conditions."