Flooding is still among the deadliest forms of weather in the United States, only second to heat as a cause of average annual fatalities. In the past decade, floods have averaged 113 American deaths per year, accounting for about 16% of all weather-related fatalities, the National Weather Service says.

Search teams plodded through mud-laden riverbanks and flew aircraft over the flood-stricken landscape of central Texas for a fourth day on Monday, looking for dozens of people still missing from a disaster that has claimed at least 78 lives.