Flood warnings from organizations like the National Weather Service (NWS) provide information to communities facing rising water levels. Understanding the distinctions between different types of flood warnings is important for public safety and effective preparation. This article focuses on areal flood warnings, explaining what they mean, their causes, and how to respond.
Understanding Areal Flood Warnings
An Areal Flood Warning indicates that flooding is expected or occurring over a broad geographic area. This type of warning is issued when water accumulation results from prolonged moderate-to-heavy rainfall or widespread snowmelt, leading to a gradual rise in water levels. The term “areal” signifies that the flooding is not confined to a single point but impacts a wider region.
Areal flood warnings differ from Flash Flood Warnings and River Flood Warnings. Flash Flood Warnings are issued for rapid and intense flooding, usually occurring within six hours of heavy rainfall, posing an immediate threat to life and property. Areal flooding develops more gradually, often taking more than six hours after rainfall begins, and may cover a large area, affecting low-lying areas, urban streets, small streams, and agricultural lands.
River Flood Warnings are issued when a river is forecast to exceed its designated flood stage at specific points, often staying elevated for days or weeks. While both areal and river flood warnings involve a slower onset than flash floods, an areal warning specifically addresses widespread inundation not tied to a single river gauge. The NWS issues these warnings to alert the public to life-threatening flooding that is in progress or soon expected.
Causes and Characteristics of Areal Flooding
Areal flooding results from several meteorological and geographical factors that lead to widespread water accumulation. A primary cause is prolonged or widespread moderate-to-heavy rainfall, where the ground becomes saturated and can no longer absorb additional water. This excess water then accumulates on the surface.
Saturated ground conditions significantly contribute to areal flooding. When soil is already full of water, its capacity to absorb further rainfall is diminished, leading to increased runoff. Significant snowmelt, especially when combined with warm temperatures and rainfall, can also rapidly release large volumes of water, overwhelming drainage systems and causing widespread inundation.
Geographical characteristics also play a role in an area’s susceptibility to areal flooding. Flat terrain and areas with poor natural drainage are particularly vulnerable as water tends to pool rather than flow away. Urbanized areas with extensive impervious surfaces, such as roads and rooftops, prevent rainwater from soaking into the ground, funneling it directly into drainage systems that can become overwhelmed. Rural areas with extensive farmlands or numerous small streams are also prone, as these streams can overflow their banks and spread water across broad agricultural lands.
Responding to an Areal Flood Warning
When an Areal Flood Warning is issued for your area, taking immediate and appropriate action is important for personal safety. Never drive or walk through floodwaters. Just six inches of moving water can knock an adult off their feet, and one foot of moving water can sweep a vehicle away. The phrase “Turn Around, Don’t Drown” serves as a reminder of this danger.
If you are in a flood-prone area, move to higher ground immediately. Securing valuables by moving them to higher floors or elevated areas within your home can help protect them from water damage. Having an emergency kit readily available is advisable. This kit should include non-perishable food, water, medications, important documents, a flashlight, and a battery-powered or hand-crank radio.
Staying informed during an areal flood event is important. Monitor local news, weather radio, and official NWS alerts for current information and instructions. If authorities advise evacuation, do so immediately, following designated routes. Disconnecting utilities like electricity and gas before evacuating, if time permits, can help prevent additional hazards.