As the Guadalupe River swelled from a wall of water heading downstream, sirens blared over the tiny river community of Comfort — a last-ditch warning to get out for those who had missed cellphone alerts and firefighters going street-to-street telling people to get out.

Officials in Texas are facing mounting questions about whether they did enough to get people out of harm’s way before a flash flood swept down the Guadalupe River and killed more than 100 people, incl