Diffuse radiation formula (Heat Stress Overlay)

The diffuse radiation is an input parameter for the PET-formula.

The diffuse radiation Q_d at time t is calculated using the following formula:

$Q_{d,t}=Q_{gl,t}\cdot f_{transmission,t}$

where,

• $Q_{gl,t}$ is the amount of sun radiation at time t, measured at a weather station.
• $f_{transmission,t}$ is the atmospheric transmission factor at time t.

Atmospheric transmission factor

The atmospheric transmission factor f_{transmission,t} is calculated as followed:

ftransmission,t	Condition
$1$	${\tau }_a<0.3$
$1.6-2\cdot {\tau }_a$	$0.3<{\tau }_a<0.7$
$0.2$	${\tau }_a>=0.7$

where ${\tau }_a$ is the atmospheric transmissivity. This is calculated as:

${\tau }_a=\frac{Q_{gl,t}}{1367\cdot \sin ({\varphi }_t)}$

where,

• $Q_{gl,t}$ is the amount of sun radiation at time t, measured at a weather station.
• ${\varphi }_t$ is the sun altitude angle in ° at time t.
• $1367$ is sourced from the DPRA Heat stress report.

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Heat Stress Module

Heat Stress Module

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