Let's look for an answer to the question Why Flood Happens. Short Answer: Heavy flooding is caused by atmospheric conditions that cause heavy rain or rapid melting of snow and ice. Geography can also increase the likelihood of flooding an area. For example, areas near rivers and cities are often at risk of flash flooding.
A flood is an overflow of water on normally dry land. Sellers can happen just about anywhere. They can cover an area with just a few inches of water, or they can bring enough water to cover a house's roof. Floods can be dangerous for communities, lasting days, weeks or sometimes longer.
Many different situations can cause flooding. Here are just a few:
- Heavy rain
- Ocean waves coming ashore like a storm surge
- Ice jams as well as melting snow and ice
- Breaking of dams or embankments
Geography can also increase the likelihood of flooding an area. For example, areas near rivers are often at risk of flooding. Urban areas (areas near cities) are also at risk of flooding because roofs direct precipitation to the ground below, and asphalt surfaces such as highways and parking lots prevent the ground from absorbing rain.
Mountains or steep hills can also increase an area's risk of flooding. Rain or snowmelt flowing down a mountain can cause streams and rivers to rise rapidly. In fact, if a storm lingers over a mountain, a creek that is only 6 inches deep can swell into a 10-foot-deep river in less than an hour.
What is a flash flood?
Flash floods are very dangerous floods that can happen with little or no warning. When there is more rain than the soil can absorb, the excess water quickly flows into rivers and streams, crushing storm drains and ditches and causing a flash flood. Flash floods can cause the water to rise significantly in a short time.
Several different weather conditions can cause heavy rainfall in an area. Tropical cyclones form in some tropical and subtropical regions, usually in summer and autumn. When they arise in the Atlantic Ocean or in the northwestern part of the Pacific Ocean and reach a certain intensity, they are called hurricanes. Tropical cyclones can produce large amounts of rain and cause flooding and flash flooding when the storm reaches land.
They can also send a stream of water from the ocean to the coastline in an event called a storm surge that inundates low-lying areas.
Another phenomenon that can cause excessive precipitation is called atmospheric river. Atmospheric rivers are long, narrow moisture conveyor belts that move through the atmosphere.
Strong atmospheric rivers can provide enormous amounts of rain and snow in California, the Pacific Northwest, and Alaska, especially during the winter months. This can cause serious flooding and mudslides.
How do satellites help during floods?
Weather satellites, such as those in NOAA's Geostationary Operational Environmental Satellite-R (GOES-R) series, watch out for atmospheric events that can lead to flooding.
For example, the GOES-R series satellites are equipped with an instrument called the Advanced Baseline Imager (ABI), which can detect and monitor the formation of atmospheric rivers. ABI can also determine the total amount of moisture in the atmosphere from the ground to the top of the atmosphere. This provides weather forecasters with useful information to improve forecasts for heavy rains and flash floods and to help keep people safe.