When rain falls across the hills and valleys of central Texas, it then rushes to lower elevations. This is what leads to the speed at which flash flooding can occur and how fast the resulting floodwaters move. As for the ground the rain falls on, beneath the top layer of soil is hard limestone. Think of that like a natural cement, which leads to runoff because it can't absorb the rainwater. And in terms of heavy rain events, those are not only increasing in number but also in intensity.
SEE ALSO: ABC13 meteorologist looks into timeline of weather alerts issued in central Texas flooding
ABC13's partners at Climate Central found that the average amount of rainfall produced by showers and storms near San Antonio has increased by 6% since 1970. And with it also being an extremely flood-prone area, any change in this statistic will lead to an increased risk of flash flooding.
Even so, floods like these in central Texas date back decades. ABC13 Meteorologist Elyse Smith went back and analyzed three previous, deadly floods that impacted this region. Two floods were the result of tropical systems. But the July 1987 Guadalupe Flood has eerie similarities to what just happened last week, including slow-moving storms that dumped heavy rain across the Hill Country. It triggered a massive surge down the Guadalupe River. Also, 10 campers at the Pot O' Gold Christian Camp near Comfort, Texas, were killed in the rushing floodwaters of the 1987 flood.
READ MORE: Deadly floods at Camp Mystic: How the tragedy compares to a similar event in 1987
Less than 10 years before that flood in 1987, there was flooding from Tropical Storm Amelia, which made landfall near Corpus Christi on July 31, 1978. ABC13 was there in central Texas to capture the aftermath of the storm and subsequent flooding. Once again, the Guadalupe River swelled after a record four feet of rain fell near Medina, Texas. Then, there's a flood that dates all the way back to the 1920s. Remnants of a hurricane in September of 1921 led to extensive flooding near both San Antonio and Austin, a flash flood that killed over 200 people. So as a rule of thumb, central Texas is susceptible to a major flood about once a decade.
Flooding is the second-deadliest weather event behind heat. Climate Central studied the cost of flooding across the country and how much is at stake to lose. Climate Central estimates the average cost of flood disasters across the nation comes to $32 billion a year. For Texas, flooding costs the state $1.5 billion a year, and that number could reach over $2 billion by the year 2050.
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