The Bureau of Meteorology has been accused of falling prey to a consultancy firm’s “land and expand” tactics as the agency’s new chief defends the $96 million cost of its widely loathed website during a combative Senate estimates hearing.

Less than one month into a new job, bureau chief executive Stuart Minchin fronted up with Environment Minister Murray Watt to a highly anticipated grilling in a late-night session in Canberra on Monday night.

The bureau’s new website has been widely criticised by farmers, site designers and politicians for changes that made it difficult to navigate, with radar maps that made it difficult to read place names.

The redesign gained national attention when it was revealed that the bureau’s initial price tag of $4.1 million was actually $96 million, including design work by private consultancy Accenture Australia.

The website upgrade was one component of the nearly decade-long Robust program, an $866 million security and technology overhaul that included forecasting and security upgrades to protect sensitive data from hacking following a serious cybersecurity breach in 2015.

Costs on the Robust program blew out by 15 per cent, Minchin told the hearing. Greens senator Barbara Pocock, a campaigner against contracting firms with questionable practices, said the initiative was a “case study of how not to do something really important”.

“There’s been a massive feeding on the public sector by the big consulting firms,” Pocock said.

“This project has been a nightmare case study in contract failure, in management of contracts, failure of leadership and completely unacceptable and unethical behaviour by the big consultants who have been at the trough through the BoM.”

Pocock cited one example of a major contractor for the website, Accenture, where the cost of one tranche of work rose in value from $33 million to $77 million following 10 contract amendments.

This contract was issued in 2019 and rose in value after a series of variations. Extra costs, additional to the $77 million contract, were incurred for security testing, launching the site and extra features, which took the total cost to $96 million.

Minchin said people only view the website platform, but the BoM’s forecasting system included 10,000 instruments in the field that feed into a supercomputer and weather models as well as operational systems.

“Our meteorologists pull those models together and create the forecasting, and that then makes it into the website,” he said.

“It was actually that end-to-end chain that cost the $96 million, not just the front end.”

Pocock said the bureau had erred in issuing open-ended contracts that enabled blowouts and criticised the reliance on current staff to manage the new programs.

“This is a firm that is famous for land and expand,” she said.

“It might have been wise to spend a little bit of money employing public servants in the BoM, who could actually manage this project, rather than requiring the BoM to manage it with their existing resources.”

Minchin conceded the bureau needed to be more transparent and publicly admit mistakes.

However, he rejected Pocock’s accusations of mismanagement: “I do take umbrage to some degree that I don’t think these contracts were as badly managed as you make out.”

Minchin said the 15 per cent blowout in the cost of the Robust program was caused in part by unforeseen COVID-19 contingencies and was within the normal range for major technology programs that typically start with a 20 per cent contingency for cost increases.

Robust had been subject to external government reviews, including eight assessments by the Finance Department.

“The most recent one finished last week, and the program received a green light from the external gateway review,” Minchin said.

Watt said the Albanese government was working to reduce reliance on external consultants.

“This [website] may well be a contract that demonstrates the need for greater oversight and of consultants and greater use of public sector capacity,” Watt said.

Pocock fired back, accusing Watt and Minchin of ignoring the culpability of the bureau.

“I don’t hear either of you saying that leadership failed, because I think it did,” she said.

Watt conceded the management of the Robust program needed greater scrutiny, stressing it was started under the former Coalition government.

“There are some questions about how this project has been managed … many of them predate Dr Minchin’s arrival, many of his team and this government,” he said.

“Please don’t be under any illusions about how seriously I, and other ministers, take these issues.”

In 2015, the bureau’s site was infiltrated by malware associated with state-sponsored cyber agents.

The incident raised fears that foreign actors could interrupt crucial weather forecasts and compromise military operations or infrastructure such as airports.

The bureau has installed a new supercomputer and the website now runs off a more secure platform that replaces the old unencrypted HTTP version, which proved too easy to hack.

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