Equipment deployed to study the impact of burn scars, flash flooding

NSSL’s mobile radar in Colorado near the burn scar. (Photo provided.)

To find ways to better protect people from flash floods, researchers are spending this summer testing equipment and evaluating methods of observing rain and flash-flood prone areas of Colorado.

Researchers from NOAA’s National Severe Storms Laboratory and the University of Oklahoma Cooperative Institute for Mesoscale Meteorological Studies are utilizing a suite of tools, including NSSL’s mobile Doppler radar in an effort to gather new observations on rain. From June through September, researchers are gathering new observations in parts of Colorado that were affected by the 2018 Spring Creek wildfire, Colorado’s third-largest wildfire which burned 108,045 acres of land.

“Federal and state partners have teamed up to provide, for the first time, a very dense observational network on the Spring Creek burn scar in Colorado,” said Jonathan Gourley, an NSSL Researcher. “In addition to the deployment of NSSL’s mobile radar, the experimental network is comprised of rain gauges, stream radars, surface velocity measurements, and soil moisture sensors, all positioned within the burn scar.”

The scientists chose these locations because areas that are burned by wildfires are more susceptible to flash flooding and debris flows, as burned soil tends to repel, rather than absorb, water. Researchers want to demonstrate the value of observations gathered by this equipment  to develop early alerts of flash flooding and debris flows on burn scars.

From June through September, researchers are gathering new observations in parts of Colorado that were affected by the 2018 Spring Creek wildfire, Colorado’s third-largest wildfire which burned 108,045 acres of land. (Photo provided)

“Burn scars are prolific at producing flash floods,” Gourley said. “The loss of vegetation and changes to the soil structure enhances the amount and velocity of runoff for a given rainfall event. Despite their devastating impacts, we have limited knowledge about the transition of rainfall-to-runoff and the tools used to forecast flash flooding on burn scars.”

The mobile radar is deployed less than 20 miles from the burn area. Researchers are using the mobile radar to monitor the lower atmosphere and supplement current NEXRAD radar coverage. The terrain in mountainous areas, like Colorado, causes difficulties for NEXRAD radars. The radar beam cannot “see” storms as it can in flatter areas, like the plains. NSSL’s mobile radar supplements NEXRAD coverage by providing more information near the ground and providing higher-resolution data for forecasters during intense rainfall events near the burn scar.

“These observations will transform our understanding and forecasting tools, which are becoming increasingly important given the expanding areas, durations, and intensities with wildfires,” Gourley said.

So far, the observations have been promising. In July, a major storm  near La Veta brought more than 1.5 inches of rain per hour and local officials provided eight reports of flash flooding. One creek overflowed by two feet and was more than 100-yards wide. Researchers collaborated with National Weather Service forecasters to provide more products and information for increased warning time.

Researchers are also testing a product that computes rainfall accumulations at 15, 30 and 60-minute time periods and compares those accumulations to United States Geological Survey-derived debris flow thresholds for the same time period. It is one of many products developed and utilized by researchers to study flooding and debris flow in areas ravaged by wildfires. 

Known as the “Wildfire Rain” product, this algorithm utilizes short-term rainfall estimation techniques to provide forecasts of how fast rain may fall and whether it is anticipated to cause flash flooding and debris flows on the burn scars. This experimental tool is used by three local NWS Colorado forecast offices and allows a longer lead time for flash flooding events.

In addition to the Wildfire Rain product, this summer researchers deployed a network of rain gauges, soil moisture sensors and stream radars in Colorado. The stream radars use remote sensing to measure the speed, depth, and flow rates in streams. These products provide on-the-ground validation of flooding at points of interest like bridges and roadways.

Monitoring efforts will continue through 2020 as researchers continue to develop ways to monitor and warn for flash flooding and debris flow.

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Experimental tool helps improve flash flood forecasts in the Northeast U.S.

Flash flood in Washington, D.C., in July. (Photo by Alek Krautmann, NOAA)

Floods and flash floods kill more people each year than any other severe weather hazard. And a few extra minutes of notice can make a big difference reducing deaths and economic loss. This is why researchers at NOAA’s National Severe Storms Laboratory are partnering with the NOAA National Weather Service Weather Prediction Center to test an experimental flash flood and intense rainfall forecasting tool.

The Warn-on-Forecast System, or WoFS, provides additional information different from what forecasters currently use because it is high-resolution and can update quickly. The weather model focuses on individual thunderstorms and hazards associated with those storms a few hours before they form and as they develop. Ultimately, the new tool will help forecasters issue flash flood warnings earlier.

The Norman-based researchers are collaborating with WPC and several NWS forecast offices to study how they are using WoFS in real-time when making forecast decisions, said Nusrat Yussouf, a research scientist at the University of Oklahoma Cooperative Institute for Mesoscale Meteorological Studies.

“Our evaluation process of research-to-operations back to research helps us improve experimental products,” she said.

This summer the prediction system proved its usefulness. For example, in July when parts of the Northeast and mid-Atlantic were inundated with intense rainfall, WPC forecasters used WoFS as they observed the perfect conditions for flash flooding over the I-95 corridor.

The WoF experimental system showed up to five inches of rain in some areas. The guidance Screenshot of WPC discussion where WoFS utilization is mentioned.provided through WoFS gave forecasters more confidence to use the phrase “flash flooding likely” when they issued area forecasts for parts of Pennsylvania and New Jersey, down to Baltimore, Washington D.C and Virginia. The storms resulted in flooded roads during rush hour, stranded motorists, cancelled and delayed flights, power outages and property damage.

This short-term exploration of the experimental WoFS’s capabilities in NWS operations is valuable for researchers at NSSL and OU CIMMS. Yussouf, whose work supports NSSL, said researchers cannot easily study NWS forecasters’ natural decision-making process in a controlled testbed environment.

“The traditional testbed experiment environments are more controlled with a routine start and end time,” she said. “We’ve created something more organic in operations that gives us insights into how that decision process occurs and how the WoF workflow may look in NWS operations in the future.”

Forecasters provide feedback to researchers throughout the experiment, including products they would like to see and what does or does not work well for them.

Yussouf said the collaboration with WPC is mutually beneficial since the Center focuses on intense rainfall and flash flooding events.

“Our goal is to help provide forecasters more tools to save lives and property,” Yussouf said. “This is one more tool to help them.”

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New research improves water hazard forecasting

Stream radar is a new tool to monitor stream levels and improve the prediction of flooding. Credit: J.J. Gourley/ NOAA
Stream radar is a new tool to monitor stream levels and improve the prediction of flooding. Credit: J.J. Gourley/ NOAA

A new program supported by NOAA’s National Severe Storms Laboratory is testing the use of stream radar to provide better measurements of stream flow and improve flood forecasting. The project, led by electronics engineer Daniel Wasielewski with the University of Oklahoma’s Cooperative Institute for Mesoscale Meteorological Studies, began in October 2016 and will span two years. NSSL research hydrologist JJ Gourley is collaborating, along with Edward Clark from NOAA’s National Water Center and John Fulton with the United State Geological Survey.

The stream radar project was borne out of a need for improved river monitoring. NOAA’s National Water Model, which became operational in June 2016, forecasts river conditions at substantially more locations than had previously been possible. The United States Geological Survey operates roughly 7,800 stream gauges in the United States, with observations critical to informing forecasters, who rely on the data to verify flood projections. Stream radars are less likely to be lost during a flood, and also have less stringent requirements for annual maintenance, power, and access. Stage and velocity levels calculated by radars will be assimilated into the NWM, and serve as additional verification points for hydrologic forecasts.

Researchers positioning stream radar above Honey Creek in Davis, Oklahoma. Credit: J.J. Gourley/ NOAA
Researchers positioning stream radar above Honey Creek in Davis, Oklahoma. Credit: J.J. Gourley/ NOAA

The NSSL/OU research team plans to install 14 stream radars on cables or bridges across rivers at predetermined, high-priority locations. Installations will take place through 2017, with results expected in early- to mid-2018. To support retrievals performed by stream radars, NSSL will also provide in-house development of a scanning lidar to produce bathymetric measurements.

Earlier this week, NOAA Research announced it would invest $6 million in programs to improve severe weather and water hazards forecasting. The stream radar program is included in this initiative, marking a significant breakthrough in NOAA’s research-to-operations efforts.

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Experimental flash flood forecasting system tested by Texas rain event

Screen Shot 2015-06-04 at 10.13.41 AMRecent flooding in Texas and Oklahoma put NSSL’s experimental Multiple Radar Multiple Sensor (MRMS) Flooded Locations and Simulated Hydrograph (MRMS-FLASH) system to a rigorous test, and researchers were pleased.

The real-time MRMS-FLASH hydrologic modeling suite produces forecasts of flash flooding that are compared to historical simulations that use more than a decade of NEXRAD-based inputs at each 1km grid point. On May 25, the City of Houston, Texas, experienced deadly flash flooding. For this event, FLASH predicted extreme water flows out to six hours in advance.

The Coupled Routing and Excess Storage (CREST) distributed hydrologic model, also a part of the MRMS-FLASH modeling suite, generates maps of streamflow and unit streamflow (cubic meters per second per square kilometer) every 15 minutes. Comparisons between the observations of flash flooding in Houston and the maps of unit streamflow show a good correspondence between areas of high unit streamflows and flash flooding.

The FLASH model represents surfaces that do not absorb water, such as in urban zones, and is able to model dynamic soil moisture conditions, and how water will be routed downstream. MRMS-FLASH has run in real-time demonstration mode for several years.

NSSL’s MRMS-FLASH system provides information and services to make communities more resilient, focusing on enhanced water forecasting and delivery services, and also helps support the NWS to evolve its operations.

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