spatialEco (version 2.0-2)

hli.pt: 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")
)

Value

Vector of McCune & Keon (2002) Heat Load Index

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")

Author

Jeffrey S. Evans <[e-mail]>

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".

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)