Home to more than 120 shops, a cinema and 34 restaurants, the Bonaire shopping centre had long been known as one of the largest in the Valencia region. After flood waters coursed through the municipality of Aldaia last week, it began making headlines for another reason: disinformation over the fate of its vast underground car park.

Online personalities, including one with more than 10 million followers, along with a prominent TV host and a far-right activist, seized on the fact that rescuers had been unable to enter the car park, falsely claiming that it contained hundreds – if not thousands – of bodies.

This week, as the flood waters receded, they were roundly discredited by Spanish police and the army, who said the car park had been searched and no bodies had been found.

It was a glimpse of the speculation, false claims and hoaxes that have surged after the deadly storm, straining a country already wrestling with the deaths of more than 200 people. “The disinformation started on Tuesday night,” said Ximena Villagrán of Maldita.es, a nonprofit foundation dedicated to factchecking. “And from that moment onwards, there was a significant explosion.”

More than a week after the floods, her organisation has confirmed more than 60 related hoaxes, echoing the kind of spread often seen in elections or in Russia’s 2022 full-scale invasion of Ukraine. “In crisis situations, which is when there is usually less certainty, is when we have big waves of disinformation,” said Villagrán.

In Spain last week, Villagrán said, false claims around the idea that the government was concealing the number of victims were in some ways facilitated by a lack of official information. It took until one week after the storm for regional judicial authorities in Valencia to confirm that at least 89 people were missing. “And that means that disinformation continued to be generated,” said Villagrán.

A day after the deluge swept away cars, bridges and rubbish containers, the head of the fire department in the province of Valencia said that hoaxes had hindered their efforts to save as many lives as possible.

“There has been talk of evacuations, of overflows, of dam breaks,” José Miguel Basset told reporters. “None of this has been correct, but it has significantly interrupted the work of the emergency teams.”

He pleaded with people to think twice before forwarding unverified information on their social networks. “I want people to realise that we are in a very complicated, very complex situation, with many people still trapped and many people who have not yet received help,” Basset said last Wednesday. “These actions, if not halted by citizens, can lead to chaos.”

Still, the steady drip of false claims continued, chipping away at the trust in officials, said Julián Macías Tovar, an activist dedicated to dismantling disinformation.

“And all of that fed into the situation that we saw on Sunday,” he said, pointing to those who hurled mud and insults at the Spanish prime minister, Pedro Sánchez, as well as the regional president, Carlos Mazón, and King Felipe and Queen Letizia.

“It’s normal for people to be angry or perhaps even violent,” said Macías Tovar. “But there was more at play: there’s always someone who speeds things up or who throws fuel on to the flames.”

Much of this comes down to the differences in the nature of false claims. “There’s disinformation, created in an industrial, intentional way by anti-democratic groups,” said Tovar. “And then you have misinformation, which spreads via confirmation bias. You see that across the political spectrum.”

In Spain last week, there appears to have been both. And those seeking to discredit the government went one step further. “They weren’t just on social media, but they showed up in person,” he said, referencing reports suggesting far-right activists had crashed the official visit with the intent of confronting the prime minister. In the process, they had stirred up locals angry over the alert that came too late and the days-long delays in getting help to affected areas.

Days after the storm, another front emerged in the wave of disinformation: narratives that falsely linked the flood to the destruction of dams. “What I can tell you is that a lot of the disinformation that is circulating now is coming from the same channels where climate change is denied,” said Villagrán.

The link prompted Greenpeace Spain to weigh in on the matter this week. “Given the evidence regarding the impacts of climate change, we cannot allow hoaxes and misinformation to prevent the necessary measures from being taken,” it said in a statement.

The flooding – Spain’s worst natural disaster in recent history – was exacerbated by the climate crisis, with global heating estimated to have made rainfall about 12% heavier and twice as likely.

Even so, information rooted in the denial of the climate emergency had flourished in recent days, in what Greenpeace characterised as a slippery slope.

“The proliferation of fake news in times of crisis can pose serious risks to people’s safety,” it noted. “Denialism, hoaxes as well as the lack of measures to stop, mitigate and adapt to climate change can cost lives.”