USGS Fire Danger Forecast
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This map 'translates the FPI map into a probability map. It shows how often we can expect a fire to burn more than 100 acres if a 1+ acre ignition occurred in a given km² grid cell with vegetation flammability conditions similar to those indicated by the FPI map. Equations for the conditional probabilities were developed using historic fire occurrence (2001-2003). The daily map is developed by plugging in the next day forecasted FPI values into the equations for the conditional probability. The map shows the frequency of times an ignition, at a given location and under similar FPI conditions for that day, burned more than 100 acres in the past. The probability is both location and date specific. Namely, for a given FPI value the probability may be different depending on the location or the day-in-year. This probability does not take into account the expected frequency of 1+ acre fire ignitions for that day and location. It simply gives the chance of a fire spreading and burning more than 100 acres IF an ignition occurs.
The next figure shows the goodness-of-fit for the large fire probability maps. It was developed from three years of fire occurrence data (2001-2003). The first thing we see in this plot is that there were no cases during the three years in the study where the estimated probability was less than 4% or greater than 45%. The green box (corresponding to green regions of the map) with model prediction category of (15-20]% states that in the three years in our study we observed a range of values between 15 to 24% with a median of 18%. For the yellow regions of the map with predicted probabilities of (20-25]% we observed a range of values between 18 to 26% with a median at 25% and so on.