Tag Archives | Data Sources

Observations and Forecasts of River Floods

A map of the Advanced Hydrologic Prediction Service (AHPS) river forecasts

Every time it rains there is a potential for flooding to occur. This is especially true after major storms. It’s also common in the spring when snow melts at higher elevations, causing mountainous streams to surge. As water from rain storms and snow melt collects in larger rivers, it raises the water level. The greater the amount of water that enters a river, the higher the level can become, and the greater the risk of a major flood event.

Each year, it is estimated that on average 133 lives are lost and over $4 billion in damages to homes, businesses, bridges and other infrastructure occurs due to inland flooding from rivers. (Coastal flooding from storm surge causes even more damage.) To help save lives and minimize damage, the National Weather Service regularly forecasts the potential for inland flooding around the country. The National Weather Services’ Advanced Hydrologic Prediction Service (AHPS) analyzes data from over 5,000 stream gauges (many of which are operated by the USGS), and combines that data with numerical models to issue daily as well as long-range forecasts of the potential for flooding to occur.

The main page of the AHPS website displays a map of all of the active stream gages in the country. Each point is colored based on the current water level. Oranges and reds signify rivers with high water levels where flooding may be occurring, while greens indicate rivers that are currently at normal levels.

The AHPS forecast map (see above) displays a subset of stations where forecasts are available. On this map, dots are colored based on the potential for flooding to occur during the next 48 hours. You can click on each point to see a graph of the river’s water level over the last 2 days, as well as the forecasted level over the next two days. Lines on each graph show the water levels where, based on past observations, minor or major flooding is likely to occur and cause damage. These graphs are updated regularly. During a major storm event, you will often see the forecast lines change over time as new data comes in and more accurate predictions can be made.

A graph of river height observations and forecast predictions on the Souris River in North Dakota.

Educator Tip: The AHPS river forecast website provides great way to introduce students to flood monitoring and forecasting. Students can investigate the real-time conditions at rivers in their local area or across the country to see where floods might occur. The national maps of real-time and forecasted flooding provides a great overview of conditions across the country, and students can easily compare these maps with weather radar data to investigate the correlation of rainfall with potential flooding.

USGS WaterWatch

USGS WaterWatch Web SiteIt’s April. And while the cold temperatures here in New Jersey make it feel like spring hasn’t quite yet arrived, the flowers are starting to poke through the ground, reminding us that spring is coming, and with it, a steady stream of springtime showers should be on their way.

Of course, when rain falls on land, much of it ends up in rivers and streams. And thanks to a network of over 3,000 stream gages monitored by the U.S. Geological Survey, we can easily study how precipitation, including rain and snow, impacts local streams, rivers and estuaries.

All of this data is available on USGS’s WaterWatch web site, which features several easy to use maps, providing a great  way to introduce streamflow data to students and the public, while showcasing how it can be used to monitor floods and droughts – critical issues related to human health, safety and well-being.

Here are a few great places to start.

Current Streamflow Map: This map displays the real-time conditions from all of the streamflow stations across the country.  Some stations measure streamflow discharge or flow rate, while other stations measure gage height, that is, how high the water level is. A few stations even measure other things like temperature, pH and dissolved oxygen. From this map, you can select an individual station to view in detail, access raw data or create custom graphs.  

On the map, each station is represented as a colored dot, whose color is based on how the current streamflow or gage height compares with past records.  Reds designate those stations that are below average while blues are above average, and green dots represent those stations that are in line with historical norms. You can also view historical streamflow maps.

Drought Map: This map highlights which areas of the country have below normal streamflow conditions, typically due to long periods of time with limited rainfall or, in mountainous areas, low levels of wintertime snowpack. Below normal streamflow is generally a good indicator of whether a drought exists, though precipitation, ground water and reservoir levels are also taken into account when declaring an official drought. (See for example, New Jersey’s Drought Information Site.)

Flood Map: Sometimes, you can have too much of a good thing. This map shows those stations stations that are currently reporting conditions drastically higher than their historically normal levels. This can often happen after severe storms with large amounts of precipitation (which is especially true after tropical storms and hurricanes), but it is also common in the spring when mountain snowpack melts. And of course, some rivers are susceptible to a springtime a double whammy.

Personally, I’ve always wondered if a more appropriate phrase for this time of year might be “April flowers bring May showers,” but to make that case, I need to dig through this data some more.

A Treasure Trove of Buoy Data

NDBC Homepage

Every day, the National Weather Service issues countless official forecasts and warnings, relying on a large network of land and ocean sensors to provide up-to-the-minute observations of the weather around the world. The accuracy of these forecasts depends largely on having enough data collected from the right places, all transmitted back to the forecaster in a timely manner. While it’s relatively easy to set up an instrument station on land and communicate with it, it’s far more difficult to do so in the ocean.

To meet this need, NOAA’s National Data Buoy Center is tasked with operating and maintaining a global network of over 250 buoys and shore stations that collect and relay (via satellite) real-time data on atmospheric and ocean conditions. As if that wasn’t enough, NDBC also collects and processes data from over 850 additional stations run by a number of collaborators, including the National Ocean Service, the Integrated Ocean Observing System and even the oil and gas industry.

Most importantly, NDBC provides their data to the world to use, for free. Their site may not be pretty, but it is an amazing resource for atmospheric and ocean data, (they even include a lot of background information) and it is an essential resource for oceanographers who need weather data to provide context to their experiments.

From the NDBC homepage, you can quickly navigate to any region of the world that you might be interested in. Clicking on any buoy or land station brings up the most recent real-time observations from that station, as well as links to additional information on the station (including 5-day graphs of each variable), and a full archive of data. The archived data files are relatively easy to use (though they do take some massaging – more on that soon), and they provide a virtual treasure trove of information to explore.

As someone who is interested in data about the natural world, and in particular about the ocean, I often find myself on the NDBC site. Whether you want to investigate physical processes like the correlation between winds and waves or between air and water temperatures, or study the differences and similarities between two locations, or review the events that occurred during past storms, the wealth of data on the buoy center’s site is sure to keep you busy for a long time.

If you have a favorite research subject or activity that you utilize NDBC data for, I’d love to hear about it. Please leave a note in the comments, or contact me.

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