The storm was a defining moment, exposing not only the destructive power of nature but also the failures of government preparedness and response. The devastation reshaped how the US thinks about disaster management — prompting sweeping reforms at FEMA, billions in levee upgrades, and groundbreaking advances in hurricane forecasting.

But experts warn that many of those hard-won lessons are now under threat. Cuts to climate forecasting programmes, a weakened federal emergency response system, and the growing force of climate-fuelled storms have left the country alarmingly exposed.

Katrina: The storm that broke the system

When Katrina made landfall on 29 August 2005 as a Category 3 storm, it was not just wind and rain that proved catastrophic. It was the collapse of New Orleans' flood defences. Built by the Army Corps of Engineers, the concrete levees and floodwalls failed, leaving most of the city underwater.

Entire neighbourhoods were wiped out. Survivors clung to rooftops waiting for rescue, while tens of thousands packed into the Louisiana Superdome without food, medicine or proper sanitation.

By the time the floodwaters receded, at least 1,833 people had died across five states. Damages, adjusted for inflation, surpassed $200 billion (€170 billion), according to NOAA. New Orleans' population fell by more than 100,000 and has never fully recovered.

Forecasting breakthroughs — and new threats

The scale of the disaster spurred a revolution in hurricane science. NOAA invested heavily in supercomputers, satellites, and research programmes. Forecasting accuracy has since improved by around 50%, saving lives and billions in economic losses by narrowing evacuation zones and giving communities more time to prepare.

Since 2023, NOAA's new Hurricane Analysis and Forecasting System has been capable of predicting storm tracks, rainfall, surge, and even tornado risk up to seven days in advance. Planned upgrades for 2025 would allow models to simulate how multiple storms interact — a critical leap in forecasting.

But these systems are fragile. Proposed budget cuts threaten NOAA's satellites, aircraft missions, and staff, leaving gaps in the very chain of data collection that underpins modern forecasting.

"NOAA saves lives. Period. Cut any link in that chain and you put people at risk," said Jeff Watters of Ocean Conservancy.

The warnings come amid an uptick in storm intensity. Hurricane Helene in 2024 was the eighth Category 4 or 5 storm to hit the US in just eight years — equal to the number that struck over the previous half-century combined.

FEMA under pressure

Meanwhile, FEMA — the agency tasked with disaster response — is facing a staffing crisis. A letter signed by more than 180 current and former FEMA employees accused the Trump administration of undermining the agency, hollowing out expertise and politicising senior leadership.

They warned that nearly a third of FEMA's permanent staff has left since January, eroding its ability to respond to major disasters.

The letter, titled the "Katrina Declaration", was stark:
"Hurricane Katrina was not just a natural disaster, but a man-made one. Two decades later, FEMA is enacting processes and leadership structures that echo the very conditions that law was designed to prevent."

The timing could not be worse. The Atlantic hurricane season is expected to be above average, and only last month flash floods in Texas killed at least 135 people, including 37 children. Experts say FEMA's weakened capacity contributed to the high death toll.

New Orleans remembers — and warns

In New Orleans, the anniversary of Katrina is being marked with a mix of grief and urgency. Survivors and community leaders will gather in the Lower Ninth Ward, where a levee breach devastated one of the city's most vulnerable, predominantly Black communities.

The commemoration will include wreath-laying, art exhibitions, and a brass band second line parade, both to honour those lost and to highlight ongoing struggles: fragile infrastructure, gentrification, and intensifying climate risks.

Organisers are calling for the anniversary to be recognised as a state holiday, framing it not only as remembrance but also as a warning.

Could it happen again?

Experts say yes — and perhaps sooner than many would like to believe. Stronger storms, a weakened FEMA, and threatened cuts to NOAA's forecasting system form a troubling picture.

"Katrina took nearly 2,000 lives and caused billions in damage. We learned hard lessons and built world-class forecasting as a result," Watters said. "Cutting those systems now — on the 20th anniversary and at the height of hurricane season — would be reckless."

Two decades after Katrina, the US faces a choice: build on the lessons of the past or risk repeating them.