Heat Load Index

Calculates the McCune & Keon (2002) Heat Load Index

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

Arguments

x	rasterLayer class object
check	(TRUE/FALSE) check for projection integrity and calculate central latitude for non-geographic projections
force.hemisphere	If country is split at the equator, force southern or northern hemisphere equation c("southern", "northern")

Value

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

Note

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.

Author

Jeffrey S. Evans <jeffrey_evans@tnc.org>

Examples

  library(raster)
  data(elev)
  heat.load <- hli(elev)
#> Using folded aspect equation for Northern hemisphere
    plot(heat.load, main="Heat Load Index")