Kangaroo Valley was hit by raging fires and floods three times in three years.

In 2019, the black summer bushfires had forced Layla Wang’s family to flee their home. Then in 2022, after floods and landslides isolated the valley, she was trapped there, spending several “stressful” weeks isolated from school – in the middle of year 12, with no access to her classes and limited resources.

“I felt like I was just in a constant state of anxiety,” she tells Guardian Australia.

“I couldn’t really receive updates, I didn’t know what was going on outside of the village and I didn’t know what was going on with my friends either. So essentially, my support system was cut off.”

The high-achieving student believes the situation also resulted in her not getting into the degree she had worked so hard for.

Experts and advocates fear the lifelong consequences facing young people are being overlooked in disaster responses as what were previously known as “one-in-a-hundred years” disasters increase in frequency and severity.

A wallaby stands in the burnt-out bush near Kangaroo Valley in 2020, shortly after the devastating black summer bushfires. Photograph: Jessica Hromas/The Guardian

A report by Deloitte, commissioned by Unicef, has found the impact of disasters on young people aged up to 24 will cost $100bn between now and 2060. The most significant cost is the loss of lifetime earnings for those who, following a disaster, do not finish high school.

The report estimates disasters reduce the likelihood of students completing year 12 by 4.2%, incurring a lifetime cost of more than $1m for each student who does not and costing the economy $5.3bn per year.

Katie Maskiell, head of policy and advocacy at Unicef, said the report shows it is crucial to keep students connected to learning after a disaster.

“That has huge implications for their future, whether or not they go onto further study, the career they might undertake, the jobs that they might be able to get in their future,” she said.

Mental health is the second-largest cost of disasters for children and young people, estimated at $662m a year.

David Rumbens, a partner at Deloitte Access Economics, said that cost comes from young people seeking treatment for up to two years following a disaster, but there are also longer-term developmental impacts that cannot be quantified.

“We do know that kids that go through a disaster are more likely to require mental health support, more likely to develop anxiety or other conditions … so a lot of that cost is [the] government providing services.”

Another significant cost is the financial impact of child abuse after a disaster, which Deloitte estimates is $192m a year. Maskiell said Unicef has found child protection systems are weakened in the aftermath of a disaster.

“We know that there can be a lot of family stress, a lot of strains and financial hardship … so we know that because of those factors, we do see increases in family and domestic violence,” she said.

‘I do feel we as young people are forgotten, especially young people in regional areas,’ says Wang. Photograph: Blake Sharp-Wiggins/The Guardian

Longterm costs worsen under higher emissions scenarios. Under a low trajectory, where emissions increase by 1.78C above 1950 levels by 2060, Deloitte estimates the cost to young people would be $8.3bn a year.

Under a higher trajectory, where emissions increase by 2.44C, the cost reaches $12.1bn a year.

Unicef is calling for the government to create a policy framework to support young people during and after natural disasters. “[We need] a better plan around the things that children need, around education and having enough supports to help them with their mental health if they’re traumatised by an event,” said Maskiell.

“[It’s] also about having the right supports and services in place for families who are experiencing hardship … [to] try and reduce incidences of child abuse.”

Wang, now 20, studies in Sydney and works as a climate ambassador for Unicef. She said young people are often overlooked during disaster recovery and that additional support when she experienced multiple disasters would have helped.

“I do feel we as young people are forgotten, especially young people in regional areas,” she said.

“[When we were evacuated] there was a sense of hopelessness … something that I would have appreciated, as I was only in high school then, was some support specifically for that.”