hli.pt: Point estimate of Heat Load Index

In jeffreyevans/spatialEco: Spatial Analysis and Modelling Utilities

Point estimate of Heat Load Index

Description

Calculates the McCune & Keon (2002) Heat Load Index

Usage

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

Arguments

alpha	numeric vector of aspect (degrees or radians)
theta	numeric vector of slope (degrees or radians)
latitude	Numeric vector of center latitude
direct	(FALSE/TRUE) default is "heatload", alternative is "direct radiation"
scaled	(FALSE/TRUE) scale metric to arithmetic scale
units	What units are slope and aspect in "degrees" or "radians"
hemisphere	Define if in "southern" or "northern" hemisphere, default is northern
force.hemisphere	Force hemisphere to southern or northern (defined in hemisphere arg_
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 a log scale 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). Note that Eq is on an arithmetic scale

Value

numeric vector of 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

# Single input
hli.pt(alpha=30, theta=180, latitude=40) 

# Results from McCune, B., and D. Keon (2002)
# Equation 1
# ln(Rad, MJ  cm–2 yr–1) -0.2551  -0.6280  0.0538  -0.6760  -1.1401  -0.2215
# arithmetic scale        0.7748   0.5337  1.0553   0.5086   0.3198   0.8013

slp = c(0, 30, 30, 0, 30, 30)
asp = c(0, 0, 180, 0, 0, 180)
lat = c(40, 40, 40, 60, 60, 60)
hli.pt(alpha = asp, theta = slp, latitude = lat)
hli.pt(alpha = asp, theta = slp, latitude = lat, scaled=TRUE)
# Equation 2
# arithmetic scale  0.8172   0.5304   0.5291   0.5706   0.3354   0.3344
hli.pt(alpha = asp, theta = slp, latitude = lat, equation = 2, scaled=TRUE)

# Equation 3
# arithmetic scale  0.9580  0.6416  0.9825  0.7430  0.4336  0.7744
hli.pt(alpha = asp, theta = slp, latitude = lat, equation = 3)
  

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