FlowAlert

How are USGS Rainfall Thresholds determined?

The USGS uses the M1 model to estimate the rainfall threshold that would have a 50% likelihood of producing a debris flow in small watersheds (<8 km²) in a burn area.  The overall rainfall threshold for the first year after fire is the median rainfall threshold for all of the small watersheds that were modeled in the entire burn perimeter to have a 50% likelihood of a debris flow. The overall rainfall threshold for the second year after fire is the median rainfall threshold for all of the small watersheds that were modeled in the entire burn perimeter to have a 75% likelihood of a debris flow. No third year after fire threshold has been established. 

What’s the difference between FlowAlert and the dashboard?

FlowAlert is software that is freely available here:

https://code.usgs.gov/ghsc/lhp/FlowAlert

The dashboard displays results from the FlowAlert software to allow for situational awareness. 

How do you get publicly available data for FlowAlert?

We use an API provided by the commercial company Synoptic. This API allows users to download data from a variety of rain gage networks including the National Weather Service, RAWS, and County networks. All of the data have a minimum timestep of 5 minutes in order to conform with Standard Hydrometeorological Exchange Format (SHEF) standards. 

How should I cite FlowAlert?

King, R., Rengers, F.K., Wedell, L., Fee, J. (2024). FlowAlert: A software designed to provide situational awareness for runoff-generated debris flows in recently burned areas, version 1.0.0, U.S. Geological Survey software release

What timezone is FlowAlert in?

All times in from FlowAlert are shown in UTC.

How often is the dashboard updated?

The dashboard is updated once every 2 hours.

How do you choose which fires that you use in FlowAlert?

When the USGS creates a new debris flow hazard assessment for a wildfire, the fire is then added to the flowalert database, so that any rain gages within 4 km of the burn perimeter can be monitored. 

How does FlowAlert quality check incoming rainfall data?

Incoming data through synoptic have some basic quality checks. 

FlowAlert additionally checks the quality of raw rainfall data by comparing the calculated intensity values to estimates from the NOAA Atlas 14 Precipitation Frequency Data Server and by running a moving average check on the calculated rainfall intensities. Information of how rainfall recurrence intervals are estimated can be found here and information on the moving average check can be found here. 

Note that there are many reasons that rainfall data can be incorrect. For example, rain gages can measure melting snow, become damaged by environmental conditions, or malfunction. Therefore, users are cautioned to use additional information from outside the dashboard before making decisions about the information that they view on FlowAlert. 

How do you estimate the rainfall recurrence intervals?

Rainfall recurrence intervals are downloaded for each rainfall station from the NOAA Atlas 14 Precipitation Frequency Data Server. When rainfall intensity values are calculated, they are compared against the downloaded rainfall estimates to see what the recurrence interval of that intensity value would be.

NOTE: The table below is an example recurrence interval table for a specific location. Each rainfall station will have its own unique recurrence interval table.

Each column represents a recurrence interval in years and each row represents a duration in minutes. The values in the table reflect the rainfall intensity value associated each duration-recurrence interval pair. For example, the 15-minute intensity associated with a 1000 year recurrence interval is 228 mm/hr.

FlowAlert compares values it calculates from data with station-specific values for recurrence intervals pulled from tables similar to the one above. For example, if FlowAlert calculated a 30-minute intensity value of 50 mm/hr, it would compare this value against the above table and conclude that a 5-year rainfall event was observed.

How is rainfall intensity calculated?

Rainfall intensity is defined as the sum of all rainfall over a defined timespan. For example, if there was a total of 100 mm of rainfall in the past 60 minutes, then the current 60-minute intensity is 100 mm/hr. This calculation is done in a moving window every 1 minute for 15, 30, and 60 minute intensity values in FlowAlert. This calculation is conducted in metric and English Units. 

Why do some gages show intensities at 15, 30, and 60 minute intervals, but other gages only show intensities at 30, and 60 minutes intervals, or just 60 minute intervals?

Intensity values are only calculated if the incoming data is precise enough to do so. For example, if the incoming data has a precipitation value every 15 minutes, then every intensity interval will be calculated. If the incoming data only has a precipitation value every 20 minutes, then only the 30, and 60 minute intensity intervals will be calculated because the incoming data doesn't have enough resolution to calculate 15 minute intensity.

How does FlowAlert define storms?

A storm starts with the onset of rainfall and continues until there is a break in rainfall that lasts 8 or more hours. For example, if a data record starts with a rainstorm that lasts 3 hours, and then there is a break of 8 hours without any rainfall, the 3 hours of rain will be labeled as storm 0. The following 8 hours are not part of storm 0. If rainfall begins again 8 hours after the end of precipitation delineating storm 0, the next storm will be labeled storm 1.

What are the two types of rainfall stations shown on the FlowAlert dashboard?

Threshold Station: This is a station where rainfall intensity has crossed a rainfall threshold in a burned area. 

Storm Station: This is a station where rainfall was measured, but the rainfall intensities were lower than the threshold. 

The reason we display both threshold and storm stations is that in areas with multiple stations it provides users situational awareness of how the spatial distribution of the rainfall. Additionally, because of the errors inherent in rainfall data this allows users a method to check if a high rain rate displayed at a threshold station is correct by looking for additional evidence of rainfall in the surrounding area. 

How to use “Recent Plot Data” on the FlowAlert dashboard?

Any rain gages that have experienced rainfall above the rainfall threshold are shown in the “Recent Plot Data” column of the dashboard. Clicking on one of the stations zooms into the station location and the attributes of the rain gages are shown. Rainfall plots from recent storms are displayed below the attribute information, and by clicking on the plot a larger view of the plot will open in a new tab. Stations are stored in the “Recent Plot Data” for 30 days before being archived. 

What are the “Fires Within Map Extent” on the FlowAlert dashboard?

This column shows all of the wildfire perimeters with debris flow hazard assessments that are visible at the current map extent. 

How can I zoom in on a specific fire on the FlowAlert dashboard?

In the top banner you can use the “Select by Fire” dropdown menu to either search a fire by name or choose from the list. 

How can I filter items shown in the FlowAlert dashboard map?

There are 3 filters in the top banner that can be used for limiting data shown on the map. 

• State Filter – allows users to filter by the state
• Select Fire Year – allows users to filter by year (going back to 2020)
• Select by Fire – allows users to select by the fire name

Users can additionally select the layers that are displayed on the map using the “layers” icon on the top right side of the map. 

Why do hazard assessment layers disappear when I zoom out?

The hazard assessment layers are available as a layer when you zoom into the map, but as you increase the extent of your map to cover a larger area they will disappear in order to create a less cluttered map view. 

Are the USGS Rainfall Thresholds changed in the dashboard?

Yes. For the first calendar year following the fire start date the first year threshold is used. This is then updated to a second year threshold when a year beyond the fire start date is passed. No thresholds are available for use beyond the first two years, but the second year threshold is displayed for visualization purposes.