Calculate flow exceedance probabilities

Calculates exceedance probabilities for a discharge vector with the Weibull plotting-position formula. Higher flows receive lower exceedance probabilities.

Usage

calc_exceedance_prob(flow, rm.zero = FALSE)

Arguments

flow

Numeric vector of flow or discharge values.

rm.zero

Logical. If TRUE, zero and negative values are omitted from the ranking and returned as NA. Defaults to FALSE.

Value

Numeric vector of exceedance probabilities with the same length as flow. Missing input values return NA.

Details

The Weibull plotting position is: $$P = \frac{\mathrm{rank}}{n + 1}$$ where rank is the descending rank of the flow value and n is the number of ranked observations.

Examples

flow_data <- c(10, 5, 0, 15, 8, NA, 0, 20)

calc_exceedance_prob(flow_data)
#> [1] 0.3750 0.6250 0.8125 0.2500 0.5000     NA 0.8125 0.1250
calc_exceedance_prob(flow_data, rm.zero = TRUE)
#> [1] 0.5000000 0.8333333        NA 0.3333333 0.6666667        NA        NA
#> [8] 0.1666667