An academic paper on global climate zones written by three Australians more than a decade ago has been named the most cited source on Wikipedia, having being referenced more than 2.8m times.

But the authors of the paper, who are still good friends, had no idea about the wider impact of their work until recently.

The paper, published in 2007 in the journal Hydrology and Earth System Sciences, used contemporary data to update a widely used model for classifying the world’s climates.

Known as the Köppen Climate Classification System, the model was first published by climatologist Wladimir Köppen in 1884, but it had not been comprehensively updated for decades.

The lead author of the paper is Dr Murray Peel, a senior lecturer in the department of infrastructure engineering at the University of Melbourne, and he co-authored the updated climate map with geography professor Brian Finlayson and engineering professor Thomas McMahon, both now retired.

“We are amazed, absolutely amazed at the number of citations,” Finlayson told Guardian Australia from his home in Melbourne. “We are not so much amazed at the fact it’s been cited as we are about the number of people who have cited it.

“It’s pleasing that research you’ve done is something other people are finding useful.”

The trio knew their paper had an impact in academic circles and in scientific literature, with the Köppen Climate Classification System used by researchers in a range of fields including geology, sociology, public health and climatology.

But Finlayson said they were unaware of the more widespread success until a journalist from Wired contacted them about the results of an analysis by Wikipedia of the top 10 sources by citation across every Wikipedia language. All 10 were reference books or scientific articles. The updated world map of the Köppen-Geiger climate classification boasted 2,830,341 citations, easily surpassing what came in at No 2, a paper published in the Journal of Physical Chemistry that had 21,350 citations.

Finlayson said the popularity of the paper emphasised the importance of open science, which is the concept that data and findings should be openly and freely available so that others can use and benefit from them. Wikipedia operates on a similar concept, and credible citations are crucial to the encyclopaedia’s reliability.

“The journal we originally published the paper in is free and open access, and we chose the journal for that reason,” he said. “People noticed and said, ‘Hey, we have an updated climate map, we’ll use that’, and then it spread.”

At the time, open access journals were rare.

“I have always been a supporter of open science,” Finlayson said. “Research is no good to anyone locked in a cupboard, or published in a journal you have to pay a lot of money to access.”

He said he first began working with paper co-author McMahon in 1981, and that they got to know Murray, who is “a fair bit younger,” when he became one of their PhD students.

“He did his PhD on global hydrology and kept working with us in that area over the years, and we are all still very good friends and kept publishing together,” Finlayson, now 73, said. “We agree on most of the serious things and then every now and then we have differences of opinion. So we talk about it, and then we set out to test who is right, and write a paper on the results.

“If you want to form an academic group of people who work together well, the fact that they’re friends helps a lot. You’re not concerned about things like someone getting more kudos than you are.”