Plot Flow Duration Curve (FDC) by evaluation periods

Generates a Flow Duration Curve (FDC) comparing simulated and observed values (e.g., streamflow), grouped by evaluation periods.

Usage

plot_fdc(
  data,
  exceedance_thresholds = NULL,
  x_label = "% of time flow is equaled or exceeded",
  y_label = "Q [m3/s]",
  epsilon_value = 0.01,
  show_legend = TRUE
)

Arguments

data

data frame. Daily flow values of simulated and observed data, typically the daily_fdc_data output from evaluate_swat. Must include columns date, source, period, and value.

exceedance_thresholds

numeric vector. Exceedance probability thresholds (e.g., c(0, 0.02, 0.2, 0.75, 1)) for vertical reference lines. Default: NULL (no lines added).

x_label

character. Label for the x-axis. Default: "% of time flow is equaled or exceeded".

y_label

character. Label for the y-axis. Default: "Q [m3/s]".

epsilon_value

numeric. Value added to flows before log transformation to avoid issues with zeros. Default: 0.01.

show_legend

logical. Whether to display the legend. Default: TRUE.

Value

A ggplot object visualizing the Flow Duration Curve (FDC).

See also

Other Performance evaluation: evaluate_swat(), fdc_signature(), gof_metrics(), pbias_fdc_midsegment(), pbias_fdc_target_segment(), plot_mean_annual_cycle(), plot_timeseries()

Examples

tmpdir <- tempdir()
get_swat_example(tmpdir)
rch_file <- file.path(tmpdir, "TxtInOut", "output.rch")
rch_data <- output_rch(
  file = rch_file, variable = "FLOW_OUTcms",
  target_id = 3, time_step = "daily",
  output_start_date = "2011-01-01"
)

observed_data <- tibble::tibble(
  Date = qobserved$Date,
  value = qobserved$Flow,
  target_id = 3
)

evaluation_results <- evaluate_swat(
  rch_output = rch_data,
  observed_data = observed_data,
  target_id = 3,
  variable = "FLOW_OUTcms",
  metrics = c("NSE","KGE","MAE","PBIAS"),
  start_dates = c("2011-01-01","2014-01-01"),
  end_dates = c("2013-12-31","2015-12-31")
)

# Plot Flow Duration Curve
plot_fdc(evaluation_results$daily_fdc_data,
         exceedance_thresholds = c(0, 0.02, 0.2, 0.75, 1))