Flooding

Floods are natural disasters that occur when an area experiences an overflow of water onto normally dry land. These events can result from various causes and have significant impacts on communities, the environment, and infrastructure. Here are key aspects of floods:

Causes of Floods

1. Heavy Rainfall: Prolonged and intense rainfall can lead to the saturation of soil, exceeding its capacity to absorb water. This runoff contributes to surface water accumulation and potential flooding.

2. Storm Surges: Coastal areas can experience flooding due to storm surges, which are abnormal rises in sea level generated by storms, especially tropical cyclones.

3. Snowmelt: Spring thaw or sudden warming can cause the melting of snow, leading to increased water runoff and the potential for river or urban flooding.

4. Dam or Levee Failures: Failure of dams or levees can release large volumes of water, causing downstream flooding.

Types of Floods

Flash Floods: Flash floods result from intense rainfall over a short period, often in mountainous or urban areas. They can lead to rapid and unexpected rises in water levels.

5. River Flooding: Overflow of rivers and streams due to excessive rainfall or the melting of snow in upstream areas can lead to river flooding.

• Coastal Floods: Result from storm surges, high tides, or tsunamis, causing seawater to inundate coastal areas.
• Urban Floods: Occur in urban areas due to inadequate drainage systems overwhelmed by heavy rainfall.
• Pluvial Floods: Also known as surface water floods, these happen when heavy rainfall creates a flood event independent of an overflowing water body.

Impacts of Floods

1. Infrastructure Damage: Floodwaters can damage roads, bridges, buildings, and other infrastructure, disrupting transportation and utilities.

2. Loss of Lives and Property: Floods pose a significant risk to human life and property. Rapidly rising water levels can lead to evacuations and, in severe cases, loss of life.

3. Economic Impact: Flooding can have long-term economic consequences, affecting agriculture, businesses, and communities. Recovery efforts can be costly.

4. Environmental Consequences: Floods can alter ecosystems, impact wildlife, and introduce pollutants into water bodies, affecting the environment.

5. Public Health Risks: Contaminated floodwaters can pose health risks, including the spread of waterborne diseases.

Flood Data Analysis

FEMA flood products

Dataset	Description	Map viewer link	Data download link
FEMA Flood map	FEMA provides flood maps for people to understand the flood risk of their community. The map can be accessed via an online viewer.	National Flood Hazard Layer Viewer
U.S. historical flood risks and costs	An interactive data tool to understand the flood cost. Flooding cost data is estimated using insurance claims from National Flood Insurance Program (data website) and FEMA's Individuals and Households Program (data website), which is also available for downloading.	View
National Risk Index (NRI)	NRI is a dataset and online tool built by FEMA to help illustrate the risk of United States communities for 18 natural hazards. It was calculated expected annual loss resulting from hazards times social vulnerability and then divided by resilience. Both composite index of all 18 hazards as well as index for each individual hazard are given. Social vulnerability and community resilience information are also given.	View	Download
FEMA web disaster summaries	This dataset contains financial assistance values, including the number of approved applications, as well as individual, public assistance, and hazard mitigation grant amounts.		Download
OpenFEMA Dataset	FEMA also provides many other open datasets on disaster information, emergency management, assistance, hazard mitigation etc. in industry standard, machine-readable formats.		Download

Historical data

Dataset	Description	Map viewer link	Data download link
USGS Historical flooding data	Information about past (from 1900 to present) regional flood events that involved a national coordinated USGS response.	Flood event viewer
NWS historical flood data	Historical flood information for the past by middle Atlantic river forecast center.		Download
USGS water data	Detailed site-level data about stream flow, such as gage height, discharge, both real-time monitoring, historical information, and 7-day forecast is provided. Gage data typically are recorded at 15- to 60-minute intervals.	View	Download
Climate Risk and Resilience Portal Data Group	Dynamical downscaled future climate projection including temperature, precipitation, and fire weather index provided by the Center for Climate Resilience and Decision Science (CCRDS) at Argonne National Laboratory. Data is at a resolution of 12 km2.	Link
Global Flood Database	It map the major flood events recorded by the DFO Flood Observatory since the beginning of the satellite records, using NASA's Aqua and Terra satellites. Population exposure estimates are derived from overlaying the flood maps with the Global Human Settlement Layer (GHSL) population data. ML-based precipitation estimates are also provided at 0.25degree resolution from 1983 to 2021.	View
World Atlas of Large Flood Events	It contains statistics of flood, such as number, duration, causes, severity, as well as consequences of flood such as fatalities, displaced and damage, from year 1985 to 2002. Note, some of the information on the website is no longer available or maintained.

Real-time monitoring

Dataset	Description	Map viewer link	Data download link
MODIS Near-real time global flood product	Near-time flood product retrieved from Terra and Aqua satellite images. It is daily, near-global, ~250 m resolution.	View	Download (detailed download instruction here)
Global Flood Monitoring system	A global flood monitoring system based on a hydrological runoff and routing model, developed by University of Maryland. It uses real-time satellite retrieved precipitation as input and has streamflow as output. 3-hourly flood Detection/Intensity for year 2001-2022 at 1/8th degree resolution is available for downloading.	View	Download
USGS water data	Detailed site-level data about stream flow, such as gage height, discharge, both real-time monitoring, historical information, and 7-day forecast is provided. Gage data typically are recorded at 15- to 60-minute intervals.	View	Download
USGS flood inundation mapper		View

Short-term outlook (up to 10 days ahead)

Dataset	Description	Map viewer link	Data download link
River flood outlook by NWS	River flood water outlook in the next 5 days by National Weather Service.	View
National flood hazard outlook by NWS	A 7-day outlook of potential flash, river, and tidal flood hazards. Both flood severity and potential impacts are given.	View
Forecast by local river forecast center	Flood and other hydrometeorological forecast by regional river forecast centers. For some river forecast center, for example, SE forecast center, flood inundation zone forecast is also given.	e.g. Northwest, southeast; California Nevada; Middle Atlantic (up to 10 days ahead)

Seasonal outlook

Dataset	Description	Map viewer link	Data download link
120-day forecast by NW River forecast center	120-day forecast for some river gages are provided. A seasonal Columbia river minimum stage outlook is also provided to assist with long-range planning.	https://www.nwrfc.noaa.gov/rfc/	Download