Heat Module overview

The DPRA Heat Module for the Heat Overlay can be used for heat stress calculations, based on geographical features and locale parameters. The final result is the physiological equivalent temperature, which is a measure of temperature which takes into account factors which can change the experience and effects of temperature.

The module performs these calculations in accordance with the DPRA Heat stress report.

Input factors

The calculation of the Heat Stress Overlays takes into account:

Meteorological circumstances such as:
- Sun angles, altitude and azimuth, dependent on date and time of day and project location.
- Air temperatures, (hourly, daily minimum and maximum);
- Global radiation, (hourly and average);
- Relative humidity (hourly);
- Wind speeds (hourly and daily average).
- Wind direction (hourly)
Spatial situation, such as:
- Land use, for fraction vegetation and rate of evaporation (Bowen ratio).
- Terrain, foliage and building heights

Calculation of Physiological Equivalent Temperature

To calculate the Physiological Equivalent Temperature (PET), we first have to determine which formula (sun or shade/night) should be used. It is selected by:

Day or night? Determined by the sun altitude angle;
Is a cell shaded? Calculated by the shade calculation model;

PET sun

The following factors influence the Physiological Equivalent Temperature for locations directly in the sun:

The atmospheric temperature, calculated by the atmospheric temperature formula;
The hourly global radiation from the sun, supplied as weather station data;
The wind speed at 1.2 meter above ground, calculate by the wind speed calculation model;
The Wet-Bulb temperature, calculated by the Wet Bulb temperature formula;
The sun altitude, calculated automatically based on the project area, date and time of day;
The Bowen ratio, an attribute obtained from Buildings or Terrain on that specific location;
The sky view factor, calculated by the sky view factor calculation model.

PET shade and night

The following factors influence the Physiological Equivalent Temperature for locations directly in the shade or at night:

The atmospheric temperature, calculated by the atmospheric temperature formula;
The wind speed at 1.2 meter above ground, calculate by the Wind speed calculation model;
The Wet-Bulb temperature, calculated by the Wet Bulb temperature formula;
The sky view factor, calculated by the sky view factor calculation model.
The diffuse radiation, calculated by the diffuse radiation formula.

Required information

In order to configure the Heat Overlay accurately additional data needs to be loaded in:

Date(s) and time of day. Also multiple consecutive days can be used. Each day-hour combination will become a result.
Daily weather station data
Hourly weather station data
Foliage heights (although a means of estimation is available)