Create a Walter-Lieth climate diagram — plot

This function creates a Walter-Lieth climate diagram, which summarizes mean monthly temperature and precipitation to visualize seasonal climate patterns. It supports both the classical version using monthly average temperature and an enhanced version using monthly mean daily minimum (Tmin) and maximum (tmax) temperatures.

Usage

plot_WalterLieth(
  X,
  diurnal = FALSE,
  obs_period = NULL,
  gcm = NULL,
  ssp = NULL,
  gcm_period = NULL,
  location = NULL,
  app = FALSE
)

Arguments

X: A data.table object produced using the function plot_bivariate_input(). This table can include more models, scenarios, and variables than are used in individual calls to plot_bivariate().
diurnal: Logical. If TRUE, the range between Tmin and Tmax is shown, representing the diurnal range for each month.
obs_period: Character (optional). One of the observation periods (e.g., "1961_1990").
gcm: Character (optional). A specific global climate model (GCM). If unspecified, then the mean of all global climate models will be shown for the specified ssp and gcm_period.
ssp: Character (optional). A Shared Socioeconomic Pathway scenario (SSP), required when a gcm_period is specified.
gcm_period: Character (optional). A GCM simulation period (e.g., "2041_2060"), used for ensemble means or GCM-specific plots. Required when a gcm_period is specified.
location: Character (optional). Include the location in plot title.
app: Logical. If TRUE, it will increase the font size.

Value

A ggplot2 object showing the Walter-Lieth climate diagram.

Details

The diagram uses the following conventions:

Temperature: red line showing mean monthly temperature. If tmin and tmax are supplied, they define a red ribbon showing the temperature range.
Precipitation: blue line showing monthly precipitation, scaled at 2 mm per °C. For months >100 mm, the scale changes to 20 mm per °C to avoid diagram distortion.
Humid periods: blue shading where precipitation exceeds temperature (P > T).
Dry periods: red shading where temperature exceeds precipitation (T > P).
Wet periods: dark grey shading where precipitation > 100 mm.
Freezing months: marked with a blue polygon along the x-axis when temperature < 0°C.

This plot helps identify wet/dry seasons, frost months, and temperature-precipitation balance.

The Walter-Lieth diagram was introduced by Heinrich Walter and Helmut Lieth in the 1960s to provide a compact visual representation of climate normals. It is particularly valuable in ecology and biogeography for characterizing climate zones and inferring environmental conditions suitable for vegetation types or agricultural use.

Interpretation tips:

Shaded blue areas indicate months where water supply exceeds potential evapotranspiration, often conducive to plant growth.
Shaded red areas suggest moisture stress periods.
Shaded black areas denote very wet months, which may correspond to tropical monsoon seasons or strong winter rains.
Polygon blocks on the baseline signal freezing months and potential frost periods.

Examples


if (FALSE) { # \dontrun{
in_xyz <- data.frame(lon = -120.3273, lat = 50.6745, elev = 384, id = 1) # Kamloops, BC

# Obtain the input data for the plot
my_data <- plot_WalterLieth_input(in_xyz, 
                               obs_period = list_obs_periods()[1],
                               gcms = list_gcms()[c(1, 4, 5, 6, 7, 10, 11, 12)],
                               ssps = list_ssps()[2],
                               gcm_periods = list_gcm_periods()
                               )

# Plot 1961-1990 climate normals
plot_WalterLieth(my_data) 

# include the monthly diurnal range
plot_WalterLieth(my_data, diurnal = TRUE) 

# Plot 2001-2020 period climate normals
plot_WalterLieth(my_data, obs_period = list_obs_periods()[1])

# Plot a single GCM projection
plot_WalterLieth(my_data, gcm = "ACCESS-ESM1-5", ssp = "ssp245", gcm_period = "2041_2060")

# Plot ensemble mean projection for an SSP and period
plot_WalterLieth(my_data, ssp = "ssp245", gcm_period = "2041_2060")
} # }