hli: Heat Load Index

In jeffreyevans/spatialEco: Spatial Analysis and Modelling Utilities

Heat Load Index

Description

Calculates the McCune & Keon (2002) Heat Load Index

Usage

hli(
  aspect,
  slope,
  latitude = NULL,
  direct = FALSE,
  scaled = FALSE,
  units = c("degrees", "radians"),
  hemisphere = c("northern", "southern"),
  force.hemisphere = TRUE,
  equation = c(1, 2, 3)
)

Arguments

aspect	terra SpatRaster class object of aspect
slope	terra SpatRaster class object of slope
latitude	Vector of center latitude of raster, if NULL automatical calculated
direct	(FALSE/TRUE) default is "heatload", alternative is "radiation"
scaled	(FALSE/TRUE) default is "heatload", alternative is "radiation"
units	Default is in "degrees", alternative is "radians"
hemisphere	Define if in "southern" or "northern" hemisphere, default is northern
force.hemisphere	Force hemisphere to southern or northern
equation	Which equation to use (1,2,3), default is 1 covering all slopes <= 90 and latitudes 0-60N

Details

Describes A southwest facing slope should have warmer temperatures than a southeast facing slope, even though the amount of solar radiation they receive is equivalent. The McCune and Keon (2002) method accounts for this by "folding" the aspect so that the highest values are southwest and the lowest values are northeast. Additionally, this method accounts for steepness of slope, which is not addressed in most other aspect rescaling equations.

The equations follow McCune (2007) and support northern and southern hemisphere calculations. The . If a country is split at the McCune (2007) folded aspect corrections for northern and southern latitudes are included. If you are bounding the equator you can use the force.hemisphere argument to choose which equation to use. Valid values for this argument are "southern" and "northern" with the default "none". Metic values are returned in ln(Rad, MJ cm–2 yr–1) however, if scale is TRUE they are returned in an arithmetic scale.

Equations - the equation number (1, 2 or 3); default is 1 (the most general one). The three equations have slightly different uses. Eq. 1 (default in the function below) is broadest in the application, covering all slopes <= 90 degrees in steepness at latitudes 0-60N, but has the lowest precision. Eq. 2 increases the precision by excluding slopes steeper than 60, an inconsequential omission for almost all data sets. Eq. 3 uses only three parameters to produce a slightly stronger model but is applicable only to latitudes 30-60N (ie., not for the tropical and subtropical region).

Value

terra SpatRaster class object of McCune & Keon (2002) Heat Load Index

Author(s)

Jeffrey S. Evans <[e-mail]>

References

McCune, B., and D. Keon (2002) Equations for potential annual direct incident radiation and heat load index. Journal of Vegetation Science. 13:603-606.

McCune, B. (2007). Improved estimates of incident radiation and heat load using non-parametric regression against topographic variables. Journal of Vegetation Science 18:751-754.

Examples

  library(terra)
  elev <- rast(system.file("extdata/elev.tif", package="spatialEco"))
  sa <- terrain(elev, v = c("slope", "aspect")) 
  heat.load <- hli(sa[[2]], sa[[1]])
    plot(heat.load, main="Heat Load Index", smooth=TRUE) 
   
  heat.load2 <- hli(sa[[2]], sa[[1]], equation = 2)
    plot(heat.load2, main="Heat Load Index eq 2", smooth=TRUE) 

jeffreyevans/spatialEco documentation built on April 5, 2025, 5:09 p.m.