This article was originally published on 8 July and has been updated.

Most residents of Kerr County, Texas, would have been asleep when flood alerts flashed up on their phones in the early hours of Friday.

A few hours later, many of them were woken by neighbours hammering on their door or their dogs frantically barking. Others would not have woken up until flood water engulfed their beds. For many, it was already too late.

The Kerr County towns that lie along the Guadalupe River, which surged more than 20 feet in less than an hour on Friday morning, bore the brunt of the floods and suffered most of the deaths.

The story leading up to this tragedy is one of grave mistakes.

It is not about what happened when the Guadalupe burst its banks, or the immediate aftermath, where rescuers frantically tried to save lives.

It is about how officials – in a Texan disaster hotspot known as Flash Flood Alley – failed to act years before.

The disaster is one of the most lethal floods in US history, with a death toll of at least 120 people - including 36 children. There are 170 people are still missing, with five young girls among them.

Donald Trump and the First Lady are set to arrive in Texas on Friday to meet with first responders and victims’ families as questions swirl over the emergency response to the floods and whether more lives could have been saved.

Authorities vowed that one of the next steps would be investigating whether enough warnings were issued and why some camps did not evacuate or move to higher ground.

Camp Mystic was built on the banks of the Guadalupe River, a well-studied, high-risk flood zone, according to mapped data from the Federal Emergency Management Agency (Fema).