GRSM_CT_FIRE_DEBRIS_PROBABILITY_15

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Service Description: GRSM_CT_FIRE_DEBRIS_PROBABILITY_15_12

Service ItemId: a2d49dab696f4b3f9e8b0208ae0fac30

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Max Record Count: 1000

Supported query Formats: JSON

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Description: Estimates of the potential likelihood of debris flow (%). These predictions are made at the scale of the drainage basin, and at the scale of the individual stream segment. Estimates of probability, volume, and combined hazard are based upon a design storm with a peak 15-minute rainfall intensity of 12 millimeters per hour (mm/h). The preliminary hazard assessment relies upon empirical models to estimate the likelihood and volume of debris flows for selected basins in response to a design storm. Beginning in 2016, the empirical models are based upon historical debris-flow occurrence and magnitude data, rainfall storm conditions, terrain and soils information, and burn-severity data from recently burned areas. Post-fire debris-flow likelihood, volume, and combined hazards are estimated at both the drainage-basin scale and in a spatially distributed manner along the drainage network within each basin. The characteristics of basins affected by the fire were calculated using a geographic information system (GIS). Debris-flow likelihood and volume were estimated for each basin outlet as well as along the upstream drainage networks (pixels where the contributing area is greater than or equal to 0.02 km2). Independent variable values were calculated for each pixel along the drainage network and summarized at the stream segment scale to obtain estimates of debris-flow likelihood and volume. The likelihood of a debris-flow in response to a given peak 15-minute rainfall intensity are based upon a logistic regression approach, which combines the following two equations: (1) P = ex / (1 + ex), Where • P is the probability of debris-flow occurrence in fractional form, and • ex is the exponential function where e represents the mathematical constant 2.718. For recently burned areas in southern California, equation 2 is used to calculate x: (2) x = -3.63 + (0.41 × X1R) + (0.67 × X2R) + (0.7 × X3R) Where • X1R is the proportion of upslope area in burned area reflectance class (BARC) Class 3 or 4 with gradients ≥23°, multiplied by the peak 15-minute rainfall accumulation of the design storm (in millimeters [mm]), • X2R is the average differenced normalized burn ratio (dNBR) of the upslope area, multiplied by the peak 15-minute rainfall accumulation of the design storm (in millimeters [mm]), • X3R is the soil KF-Factor (Schwartz and Alexander, 1995) of the upslope area, multiplied by the peak 15-minute rainfall accumulation of the design storm (in millimeters [mm]). Likelihood values predicted by the equation potentially range from 0 (least likely) to 1 (most likely). The predicted likelihood values are assigned to 1 of 5 equal interval classes for cartographic display, and are represented as a percentage likelihood (rather than a ratio).

Copyright Text: USGS

Spatial Reference: 26917 (26917)

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Units: esriMeters

Child Resources: Info

Supported Operations: Query Create Replica

GRSM_CT_FIRE_DEBRIS_PROBABILITY_15_12 (FeatureServer)