Add drought period (bands or markers) to a spei time series plot

Adds shaded polygons, vertical lines, or both to a ggplot object to highlight drought events, based on a drought assessment summary (as returned by droughts()). Optionally, labels or points can be added to indicate drought severity.

Usage

add_drought_events(
  p,
  drought_assessment,
  which_events = c("all", "top"),
  metric = c("duration", "severity", "intensity", "lowest_index"),
  top_n = 5,
  type = c("line", "polygon", "both"),
  line_col = "black",
  line_type = "dashed",
  pol_fill = "gray70",
  pol_alpha = 0.5,
  show_severity = FALSE
)

Arguments

p: A ggplot object created by plot_drought_ts().
drought_assessment: A data frame with columns minyear, month_peak, d_duration, d_severity, and others, as returned by droughts().
which_events: Display "all" droughts or only the "top" events.
metric: If which_events = "top", use this column to rank events. Options: "duration", "severity", "intensity", "lowest_index".
top_n: Number of top events to display when which_events = "top". Default to 5.
type: Type of marker to display: "polygon" (shaded bands), "line" (vertical lines at peak), or "both".
line_col: Color of vertical line (if used).
line_type: Line type of vertical line (e.g. "dashed", "solid").
pol_fill: Fill color of polygon (if used).
pol_alpha: Transparency of polygon fill.
show_severity: Logical. If TRUE, plots a point and label for severity at top of each event.

Value

A modified ggplot object.

Examples

data(spei_granada)

result <- droughts(spei_granada, vname = "spei12", threshold = -1.28)

p <- plot_drought_ts(spei_granada, vname = "spei12")

add_drought_events(
  p,
  drought_assessment = result$drought_assessment,
  which_events = "top",
  metric = "severity",
  top_n = 3,
  type = "both",
  show_severity = TRUE
)