New TACLS Software Uses Satellites and Machine Learning to Target Earlier Flash Flood Alerts

The need for earlier warnings was evident on June 9, when Laura Lin was working from her home in Lanesville, a rural southern Indiana town about 15 miles from the Kentucky border. Lin was on a Zoom call and did not immediately realize that heavy rain outside had begun to flood her yard. She later saw pieces of her wood floating near the barn, closed her laptop, woke her children and told them something was wrong. Lin and her family got out safely and sheltered at a neighbor's house, but Lanesville received more than 8 inches of rain within a few hours that day, far above the threshold for what is considered heavy rainfall. The water was gone a few hours later. Lin said the warnings to get on roofs did not arrive until she was already at the neighbor's house, and that people in town were already flooded when alerts were sent out.

Floods are the second-deadliest type of weather event in the United States and the deadliest globally, according to the article. Just 6 inches of fast-flowing water can knock an adult off their feet, 12 inches can lift a car, and 2 feet can move larger vehicles such as trucks and SUVs. A warming climate means more instances of extreme rainfall in the United States, creating more opportunities for floods to occur. The article also cites deadly flash flooding in Nepal in August caused by a glacier collapse as an example of the power of water to devastate communities worldwide.

TACLS uses satellites and machine learning to try to spot areas that could flood sooner and help the National Weather Service make better decisions about issuing flash flood alerts. Ivory Small, science and operations officer at the NWS San Diego Weather Forecast Office, said the system 'will help you save lives.' Without TACLS, Small said, a storm moving into an area 'could kill some folks.' With TACLS, he said, 'you can put out the warning and save some folks.'

Weather forecast offices are responsible for issuing severe weather alerts, including flash flood warnings. Jayme Laber, senior service hydrologist for the NWS Weather Forecast Office in Oxnard, California, which oversees the Los Angeles area, said there are 122 such offices throughout the United States and its territories. Small and Laber worked closely on the TACLS project with a broader team of scientists and researchers, and they hope the project will streamline weather alerts. To understand TACLS, Laber said, it is important to first understand how the NWS issues flood alerts.

Currently, staff in weather forecast offices use a variety of tools to monitor flood conditions. They rely on rain and stream gauges to tell them how much water is in a certain place at any given time, Laber said, and they track developing storms using satellites and weather radars. The staff monitors rainfall, while computers also alert them when it rains more than what is considered safe for a specific area. Laber said flash flood guidance is based on factors including the type of soils and the steepness of slopes, so forecasters know that if a certain amount of rain falls in a certain amount of time in an area, it could result in flash flooding. All of that, plus years of expertise inside those offices, determines whether someone presses a button to issue a flood alert, he said.

Laber described the levels of flood alerts. A watch is the least serious and means there is a chance a flash flood could happen. It might be issued anywhere from 12 to 48 hours in advance. He said local emergency teams should start working on flood protection measures when a flood watch is issued, so there is enough time to prepare before people are stuck and forced to find higher ground. Response teams might review evacuation plans, set up sandbags and road barriers, and identify the highest risk areas ahead of a potential flood. An advisory is the next level up. It might be flooding, but it is more nuisance-level and is not going to threaten life or property, Laber said. A warning is the most serious alert. Small said it represents a life-and-death possibility of being swept off your feet or being run over by a car floating down the stream. The NWS differentiates a regular flood from a flash flood based on time, Small said. If an area floods in under six hours, it is a flash flood.