A flash flood watch is a rapid rise (minutes to hours) and surprising water levels affecting any part of a watershed. These floods are mostly due to heavy and localized rainfall associated with thunderstorms, storms, cyclones, or, more rarely, glacial disasters, causing sudden and sudden flooding of the hydrographic network. This often causes significant and rapid water circulation and flooding outside of their traditional places, sometimes quite far from this network (for example: outdoors, in a garden). This amazing, unexpected and cruel effect is the cause of many casualties.
The duration of their evolution (rising then lowering the water level) is less than 6 hours. Their water flow at the peak flood level is relatively high.
A flash flood watch usually occurs at the outlet of a stream. It then spreads, increasing in size, especially if the precipitation is heavy and continuous. They are short, strong and can have serious consequences for a person’s life. These are usually unforeseen circumstances, hence their name.
How dangerous is a flash flood watch?
Flash floods are a serious hazard, causing more deaths in the United States on average per year than lightning, tornadoes, or hurricanes. Flash floods can also lead to the deposition of large amounts of sediment on floodplains and destroy vegetation cover that is not adapted to the conditions of frequent flooding.
A Flash flood watch occurs most often in dry areas that have received recent precipitation, but can be seen anywhere downstream of the source of the precipitation, even many miles from the source. In areas on or near volcanoes, flash floods also occurred after eruptions, when glaciers melted due to extreme heat. A flash flood is known to occur in the highest mountain ranges of the United States and are also common in the arid plains of the Southwestern United States.
The United States National Weather Service gives “Turn Around, Don’t Drown” advice for flash floods; that is, it recommends that people leave the flash flood area rather than attempt to cross it. Many people tend to underestimate the danger of flash floods. The most dangerous flash flood watch are their sudden nature and rapid flow of water. The vehicle provides little to no protection against sweeping; this can make people overconfident and less likely to avoid flash flooding. More than half of the deaths associated with flash floods are people driven away by cars while trying to cross flooded intersections. [four]Just 2 feet (0.61 m) of water is enough to blow away most SUV-sized vehicles. The US National Weather Service reported in 2005 that, using a 30-year national average, more people die each year from floods, averaging 127, than from lightning (73), tornadoes (65), or hurricanes.
Causes of Flash flood Watch
It can be caused by heavy rain associated with a severe thunderstorm, hurricane, tropical storm, or meltwater from ice or snow flowing over ice sheets or snowfields. A Flash flood watch can also occur after the collapse of a natural ice or debris dam or human structure such as an artificial dam, as happened before the flood in Johnstown in 1889. Flash floods differ from normal floods in that less than six hours elapse between rain and the onset of the flood.
A Flash flood can also be caused by heavy rainfall generated by hurricanes and other tropical storms, as well as the flash melt effective dams. Human activities can also cause flash floods. When dams fail, large amounts of water can be released and destroy everything in its path.
In deserts, flash flood watch can be especially deadly for several reasons. First, storms in dry regions are infrequent, but they can deliver huge amounts of water in a very short time. Second, these rains often fall on poorly absorbent and often clay soils, greatly increasing the amount of runoff that rivers and other waterways have to manage. These regions generally lack the infrastructure that wetter regions need to divert water from structures and roads, such as storm drains, culverts, and catchment areas. Either due to sparse population or poverty, or because residents feel that the risk of flash flood watch is not high enough to justify the expense. In fact, in some areas, desert roads often cross dry rivers and stream beds without bridges. From the driver’s point of view, there can be clear weather where a river suddenly forms in front of or around the vehicle in a matter of seconds. Finally, the lack of regular rainfall to clean water channels can lead to flash flood in deserts, accompanied by large amounts of debris such as rocks, branches, and logs.
Read: Fashion Industry Amid COVID-19 Outbreak
Flash Flood Watch Management System
The Flash Flood Management System (FFGS) was designed and developed by the Center for Hydrological Research, a non-profit public benefit corporation located in San Diego, California, USA, for use by meteorological and hydrological forecasters worldwide. The main purpose of FFGS is to provide operational forecasters and disaster management agencies with real-time information guidance products regarding the threat of small-scale flash floods in a specific region (e.g., a country or part of a country, several countries combined). FFGS provides the necessary products to support the development of flash flood warnings related to rainfall, using precipitation from remote sensing (e.g. radar and satellite rainfall estimates) and hydrological models. FFGS results are provided to users to support the analysis of weather events that can cause flash flood watch (e.g. heavy rains, precipitation on saturated soils) and then to quickly assess the possibility of flash floods at a given location..
For local flash flood threat assessment, the FFGS is designed to allow product adjustments based on the forecaster’s experience with local conditions, the incorporation of other information (e.g. numerical weather prediction results) and any last-minute local observations (e.g. non-traditional rain gauge data) or reports from local observers. The system supports flash flood hazard assessment on an hourly or six-hour scale for river basins ranging in size from 25 to 200 km. 2 in size.
Technical elements of a flash flood watch
Important technical elements of a flash flood guidance system are the development and use of an offset- and/or satellite-corrected precipitation field, and the use of hydrological land surface modeling. The system then provides information on precipitation and hydrological response, two important factors in determining the possibility of a flash flood watch. The system is based on the concept of guidance on flash floods and flash flood hazards. Both indices provide the user with the information needed to assess the possibility of flash flooding, including an assessment of the uncertainty associated with the data.
Read More About: Haze Registering
Flash Flood Watch Guidance
The amount of precipitation of a given duration in a small river basin required to create low flood conditions (full bank) at the outlet of the basin. Flash flood watch is estimated to have a duration of up to six hours, and river basin areas are sized to allow reasonable estimates of rainfall from remotely sensed and in situ data. In such a case, the flash flood guideline is an index that indicates how much precipitation is needed to overcome the storage capacity of soils and canals and cause minimal flooding in the basin.
Flash Flood Threat
Precipitation of a given duration that exceeds the appropriate value in the Flash Flood Watch Guidelines. Flash flood threat, when used with present or forecast rainfall, is an index that gives an indication of areas where flooding is imminent or occurring and where immediate action is or will be required in the near future.
