NCL Home > Documentation > Functions > Heat stress


Compute a simplified human discomfort index.

Available in version 6.4.0 and later.


load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/heat_stress.ncl"  ; This library is automatically loaded
                                                             ; from NCL V6.5.0 onward.
                                                             ; No need for user to explicitly load.

	function heat_discoi (
		t          : numeric,  
		twb        : numeric,  
		iounit [1] : integer,  
		opt        : integer   

	return_val [dimsizes(t)] :  float or double



Scalar or array containing temperature(s) [ units see iounit ].


Scalar or array containing vapor pressure (Pa).


An integer array of length 2 which specifies the units of the input t and returned heat_index:

  • iounit=0 input t (degC)
  • iounit=1 input t (degK)
  • iounit=2 input t (Farenheit)


Currently not used. Set to zero.

Return value

A scalar or an array of the same size and shape as t. The output will be double if t or rh is of type double. This is a unitless quantity.


This is the discomfort index (DI) calculated via equation 10 in Buzan et al (2015). Specifically:

     DI = 0.5*t + 0.5*twb 
The DI values are an indicator of threats to populations:

    DI of 21-24 less than 50% of population is in discomfort 
    DI of 24-27 more than 50% of population is in discomfort 
    DI of 27-29 most of the population is in discomfort 
    DI of 29-32 severe stress
    DI of 32+   state of emergency

    Epstein, Y., and D.S. Moran (2006) 
            Thermal comfort and the heat stress indices,
            Ind. Health, 44, 388-398.

    Buzan, J.R. et al (2015): 
           Implementation and comparison of a suite of heat stress metrics
              within the Community Land Model version 4.5
           Geosci. Model Dev., 8, 151-170, 2015

See Also

Heat and Stress functions


Example 1:

   t      = 30.5
   twb    = 24.25
   discoi = heat_discoi(t, twb, (/0,0/), 0)
The output is:

    Variable: discoi
    Type: float
    Total Size: 4 bytes
                1 values
    Number of Dimensions: 1
    Dimensions and sizes:	[1]
    Number Of Attributes: 4
      long_name :	discomfort index
      units :	degC
      info :	human discomfort due to heat and humidity: eqn 10 of Buzan et al (2015)
      NCL :	heay_discoi
    (0)	27.375