The risk of the catastrophic flooding that struck Texas Hill Country as people slept on July 4 and left at least 120 dead was potentially underestimated by federal authorities, according to an ABC News analysis of Federal Emergency Management Agency data, satellite imagery and risk modeling.

On Wednesday, hundreds prayed, wept, and held one another at a prayer service, among the first of many somber gatherings to come in the weeks ahead.

The loss of more than 100 lives, many of them children, to Hill Country floods over the July Fourth weekend has shaken Texans to the core. Closer to home, at least 16 people have died in floods in the Austin area.