# USGS Science to Keep Us Safe: Floods and Drought

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The scarcity or overabundance of water presents some of the most dangerous, damaging and costly threats to human life, ecosystems and property in the form of drought, floods and debris flows.

A National Oceanic and Atmospheric Administration assessment of severe weather and climate event costs found that, on average, droughts and floods cost about $9.5 billion and$4.3 billion per event, respectively.

On April 10, USGS hydrographer Josh Sundberg measures Red River water flowing over the road in East Grand Forks, Minnesota as flood protection walls prevent further flooding.
(Credit: Peter Goettsch, USGS. Public domain.)

Taking the Pulse on the Nation’s Water

The USGS nationwide streamgage network provides emergency managers with real-time information to monitor floodwaters across the nation. The data collected by about 11,300 gages across the country provide vital information to the U.S. Army Corps of Engineers, the National Weather Service, the Federal Emergency Management Agency and other federal, state and local agencies, enabling them to make river forecasts, operate flood control structures and make important emergency management decisions.

Keeping Communities Safe

USGS science information helps safeguard communities during water-related severe weather or climate events. USGS science and data help to minimize the loss of life and property due to hazards by supporting flood forecasting, informing drought and post-fire conditions, and monitoring floods, debris flows and storm surge during hurricanes and other low-pressure systems and tsunamis. During flood events, USGS crews are deployed into the field to verify flood data and collect additional measurements needed by partners.

Coming Soon – A New Map (or App) for Flood Preparedness

When water levels are rising, it can be hard to quickly get all the information you need about your area, especially when you’re not in front of a computer. In the coming weeks, the USGS will be releasing a new cutting-edge map that will provide critical current water information and NWS forecast information at your fingertips on a desktop, smartphone or other mobile device.

Now you don’t have to search multiple sources when you want the latest information on floods and droughts, or when you’re just deciding your next recreation destination. The upcoming USGS National Water Dashboard presents real-time stream, lake and reservoir, precipitation and groundwater data for more than 13,500 USGS real-time observation stations across the country. This information is shown along with weather data such as radar, watches and warnings, past precipitation totals, precipitation forecasts and drought conditions from other sources. The NWD will also link to the USGS WaterAlert system, which sends out instant, customized updates about water conditions.

Deploying Equipment Before a Flood

If flooding is expected due to a hurricane or tropical storm, USGS field crews will deploy to the storm’s projected path along the coast to install special water-level measuring instruments called storm-tide sensors. These sensors record data that track storm tides and coastal flooding. This information helps USGS and NOAA scientists improve forecast models. It also helps relief efforts by FEMA and other federal, state and local agencies by pinpointing the areas hardest hit by storm-tide flooding.

Storm-tide sensor information can also help engineers design structures to better withstand floods and assess how well dunes and wetlands reduce storm damage. It can help inform land-use practices and building codes, which can lead to more resilient coastal communities.

USGS crews may also install rapid-deployment gages at locations that are not monitored year-round like permanent streamgages but are at risk of flooding due to an approaching storm. These RDGs provide real-time information on water levels, precipitation, wind speed, humidity and barometric pressure to assist emergency managers tracking floodwaters. RDGs can be quickly installed at critical locations to augment the USGS streamgage network.

You can track storm-tide sensor and RDG deployments and view past storms on the USGS Flood Event Viewer and see USGS streamgage readings in real time on both the viewer and the USGS National Water Information System.

USGS scientists measures a high-water mark. Credit: USGS, public domain.

How High Did the Water Reach?

After the floodwaters subside, the USGS starts the extensive effort of finding high-water marks. During a flood event, rising waters are loaded with floating debris, seeds and dirt that can stick to buildings, trees or other structures. Once floodwaters recede from their highest peak, the line of debris left behind is a high-water mark and it can indicate to scientists the highest point the flood reached. But, these marks are fragile and easily destroyed – both by people cleaning up and by natural weathering – so collecting them is a time-sensitive effort.

After most major floods, the USGS partners with FEMA, USACE, NWS and other agencies to identify high-water marks throughout the affected areas. Depending on where these high-water marks are located, they can be used for a variety of purposes, like improving computer models used for predicting the severity of future floods.

One of the most important uses of high-water-mark data is so FEMA can revise their flood hazard maps. These maps help identify areas that are likely to experience high water in the event of a flood that has a 1% chance of happening in any given year. These floods, often referred to as 100-year floods, are the most common severe inundation events and serve as the foundation for flood management planning.

Another significant use for these high-water marks is the USGS Flood Inundation Mapping effort. These maps are developed using models that incorporate high-water marks, streamgage and storm surge information. The maps can be used by resource managers to assist in updating building codes, verifying safe evacuation routes, bridge design, environmental assessments and other community planning efforts.

Drought ruined soybean crop in Sumter County, Georgia by Alan Cressler. Credit: USGS, Public domain.

A Flood of Information – Even During Drought

Agricultural crops can wither in a flash when the days turn hot, the air dries, the rain stops and moisture evaporates quickly from the soil. The early warning Quick Drought Response Index, or QuickDRI, can help alert managers and others as drought conditions occur. QuickDRI serves as a weekly drought alarm, providing an indicator of emerging or rapidly changing drought conditions.

Like its companion Vegetation Drought Response Index, or VegDRI, which portrays drought’s effect on vegetation conditions, QuickDRI relies on a number of remotely-sensed indicators. Decades of satellite data housed at the USGS Earth Resources Observation and Science, or EROS, Center provide a resource for assessing abnormal vegetation and climate conditions over a longer historical period.

However, VegDRI is a seasonal drought indicator. For faster-moving droughts, QuickDRI was developed to detect drought’s effects much more quickly.

Looking Towards the Future

As the Atlantic Coast prepares for upcoming storms and the West experiences drought, the USGS will continue to provide data to help resource managers plan for the future.