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 = TRUE,
  force.hemisphere = c("none", "southern", "northern")
)

Arguments

alpha	Aspect in degrees
theta	Slope in degrees
latitude	A latitude representing the centrality of the data
direct	Boolean (FALSE/TRUE) Return direct incident radiation else HLI (default)
scaled	Boolean (TRUE/FALSE) Apply arithmetic scale using EXP(h)
force.hemisphere	If country is split at the equator, force southern or northern hemisphere equation c("southern", "northern")

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 account for steepness of slope, which is not addressed in most other aspect rescaling equations. HLI values range from 0 (coolest) to 1 (hottest).

The equations follow McCune (2007) and support northern and southern hemisphere calculations. The folded aspect for northern hemispheres use (180 - (Aspect – 225) ) and for Southern hemisphere ( 180 - ( Aspect – 315) ). If a country is split at 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".

Value

Vector 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 point input
hli.pt(theta=180, alpha=30, latitude=40) 

# Multiple input, returns results from 
#   McCune, B., and D. Keon (2002)
# Raw -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(theta = slp, alpha = asp, latitude = lat)
  

jeffreyevans/spatialEco documentation built on April 4, 2024, 10:53 a.m.