perrette / wbgt

Python wrapper for Liljegren's WBGT calculation

wbgt

This code is a python wrapper around Liljegren's original C code. Builds on work by Max Lieblich, University of Washington, 2016, who modernized the original code so that it interfaces nicely with R (or python's ctypes).

This python package can be used to estimate wet bulb globe temperature (WBGT) from datasets of standard meterological measurements using models developed by Liljegren et al (1). See documentation in the original repository.

Sensitivity test (see notebook):

Wet-bulb glob temperature contours as a function of air temperature and relative humidity. 31C is shown. Wet-bulb temperature 31C contour is shown as dashed line. Wet-bulb temperature is consdiered critical at 31C, according to the PSU Heat project. Quick lookup on Wikipedia shows that wet-bulb globe temperature in the range of 28-33 degC mark a transition toward restricting outdoor activities. The color scale on the plot below highligh 35 degC as middle point. Consider the reddish area unsafe!

This readme focuses on modifications made since it was forked. I only keep the references at the end.

Install

git clone and python setup.py install or:

pip install git+https://github.com/perrette/wbgt.git

Functions available in the wbgt module

The functions below are very thin wrappers around the original C code using ctypes. See original C code for documention.

wbgt(tk, rh, pres, speed, solar, fdir, cza): Tg, Tnwb, WBGT

This is simplified function of calc_wbgt, which takes actual wind speed, solar radiation, cos azimuth angla and fraction of direct irradiance directly What it leaves out:

• conversion to degC to Kelvin (expected inputs are in K, for consistency with other functions)
• conversion of relhum (%) to rh (fraction, for consistency with other functions)
• calculation of solar, fdir, cza, for greater modularity (e.g. always calculate max wbgt at noon...) and to use sun from climate models (see calc_solar_parameters)
• conversion of wind speed at arbitrary height to 2-m wind speed (see estimate_windspeed)

calc_solar_parameters(year, month, dday, lat, lon, solar): solar, cza, fdir

solarposition(year, month, day, days_1900, latitude, longitude): ap_ra, ap_dec, altitude, refraction, azimuth, distance

estimate_windspeed(zspeed, speed, solar, dT, cza, urban) : wind speed at 2 m

References

1. Liljegren JC, Carhart RA, Lawday P, Tschopp S, Sharp R. Modeling the wet bulb globe temperature using standard meteorological measurements. J Occup Environ Hyg. 2008;5(10):645-55.
2. Yaglou CP, Minard D. Control of heat casualties at military training centers. AMA Arch Ind Health. 1957;16(4):302-16.
3. Lemke B, Kjellstrom T. Calculating workplace WBGT from meteorological data: a tool for climate change assessment. Ind Health. 2012;50(4):267-78.