Plot Drought Index Time Series with Positive/Negative Bars

Creates a bar plot of a drought-related time series (e.g., SPEI or SPI), where values above and below zero are colored differently. Optionally, the time series can be aggregated and displayed by year.

Usage

plot_drought_ts(
  df,
  vname,
  title = NULL,
  date_col = "date",
  pos_color = "blue",
  neg_color = "red",
  zero_line_color = "black",
  zero_line_linetype = "solid",
  by_year = FALSE,
  y_axis_title = NULL
)

Arguments

df: A data.frame or tibble containing the time series data.
vname: A string. Name of the numeric column representing the drought index.
title: An optional character string for the plot title.
date_col: A string. Name of the column containing date information (default is "date").
pos_color: Color used for positive values (default is "blue").
neg_color: Color used for negative values (default is "red").
zero_line_color: Color of the horizontal line at zero (default is "black").
zero_line_linetype: Line type for the horizontal zero line (default is "solid").
by_year: Logical. If TRUE, aggregates the drought index by year and plots annual means (default is FALSE).
y_axis_title: Optional label for the y-axis. If NULL, the name of vname is used.

Value

A ggplot object representing the drought index time series as a bar plot.

Details

This plot is useful for visualizing the temporal dynamics of drought indices, highlighting positive (wet) and negative (dry) periods. When by_year = TRUE, the function averages the index per year and plots one bar per year.

Examples

data(spei_granada)
plot_drought_ts(spei_granada, vname = "spei12", title = "SPEI-12 Time Series")

plot_drought_ts(spei_granada, vname = "spei12", title = "SPEI-12 Annual Mean", by_year = TRUE)