Heat Module theory: Difference between revisions

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This page described the algorithm prescribed by the DPRA report.
This page describes the algorithm prescribed by the {{Template:Heat_DPRA_Report}}. For a visual overview of the Heat Stress Module, see [[Heat_Stress_module_overview|Heat Stress Overview]].
==Algorithm==
The calculation prescription of the DPRA report is implemented as followed:


Calculate once at the start:
At the start of the calculation, the following data is pre-calculated for each cell:
# the sky view factor, based on the terrain height, buildings and foliage height.
# The [[foliage height calculation model (Heat Overlay)|foliage height calculation model]] is used to calculate the [[Foliage result type (Heat Overlay)|foliage height]] (if applicable).
# Calculate the average vegetation fraction and average sky view factor. The average window is based on a wind direction and speed. For more information on this averaging window, see [[Average_step_(Heat_Overlay)| average step]].
# The [[sky view factor calculation model (Heat Overlay)|sky view calculation model]] is used to calculate the [[Sky view result type (Heat Overlay)|sky view factor]].
# Calculate per cell the urban heat island effect value. See [[UHI_formula_(Heat_Overlay)|Urban heat island formula]].
# The [[average calculation model (Heat Overlay)| average calculation model]] is used to calculate the [[vegetation avg result type (Heat Overlay)|averaged vegetation fraction]] and the [[Sky view avg result type (Heat Overlay)|averaged sky view factor]].
# The [[UHI formula (Heat Overlay)|urban heat island formula]] is applied to calculate the [[Uhi result type (Heat Overlay)|urban heat island effect value]].


Next, for each timestep, calculate the following:
Then, for each timeframe, the following data is calculated per cell:
# Per cell: does it lies in sun or if sun rays are blocked by a building, foliage or landscape features. See [[Shade_calculation_(Heat_Overlay)|Shade calculation]];
# The [[temperature formulas (Heat Overlay)|temperature formulas]] are applied to calculate the [[temperature atmosphere result type (Heat Overlay)|atmospheric temperature]], and the Wet-bulb temperature.
# Per cell: the atmospheric temperature and the Wet-bulb temperature. See [[Temperature_formulas_(Heat_Overlay)|Temperature formulas]];
# The [[shade calculation model (Heat Overlay)|shade calculation model]] is used to determine whether the cell is [[shade result type (Heat Overlay)|shaded]].
# Per cell: the diffuse radiation, based on the sun [[Hourly_radiation_(Heat_Overlay)|radiation]] and [[Sun_altitude_(Heat_Overlay)|altitude angle]]. See [[Diffuse_radiation_formula_(Heat_Overlay)|diffuse radiation formula]];
# The [[Wind calculation model (Heat Overlay)|wind calculation model]] is used to determine the [[Wind speed result type (Heat Overlay)|wind speed]] (using [[Weather station (Heat Overlay)|weather station data]]).
# Per cell: the physiological equivalent temperature (PET). If it is night or the cell is in the shade, the [[PET_formulas_(Heat_Overlay)#PET_Shade_and_Night_formula|shade formula]] is used, else the [[PET_formulas_(Heat_Overlay)#PET_Sun_formula|sun formula]] is used.
# The [[Diffuse radiation formula (Heat Overlay)|diffuse radiation formula]] is applied to calculate the diffuse radiation.
 
# The [[PET formulas (Heat Overlay)|physiological equivalent temperature formulas]] are applied to calculate the final [[Pet result type (Heat Overlay)|physiological equivalent temperature (PET)]].
 
{{article end
 
|notes=
==Notes==
* Each [[Dates_(Heat_Overlay)|date-time]] created in the Heat Overlay configuration wizard will be its own timestep.
* In the DPRA report step description, the atmospheric temperature is only calculated once. However, the Atmospheric temperature formula used an hour of day input parameter and should therefore be performed each timestep.
* In the DPRA report step description, the atmospheric temperature is only calculated once. However, the Atmospheric temperature formula used an hour of day input parameter and should therefore be performed each timestep.
* We have not implemented an automatic translation to future KNMI WH-scenarios. However, since users can provide their own weather station data, it can be configured manually.
}}
{{HeatOverlay_formula_nav}}

Latest revision as of 15:15, 23 January 2024

This page describes the algorithm prescribed by the DPRA Heat stress report. For a visual overview of the Heat Stress Module, see Heat Stress Overview.

Algorithm

The calculation prescription of the DPRA report is implemented as followed:

At the start of the calculation, the following data is pre-calculated for each cell:

  1. The foliage height calculation model is used to calculate the foliage height (if applicable).
  2. The sky view calculation model is used to calculate the sky view factor.
  3. The average calculation model is used to calculate the averaged vegetation fraction and the averaged sky view factor.
  4. The urban heat island formula is applied to calculate the urban heat island effect value.

Then, for each timeframe, the following data is calculated per cell:

  1. The temperature formulas are applied to calculate the atmospheric temperature, and the Wet-bulb temperature.
  2. The shade calculation model is used to determine whether the cell is shaded.
  3. The wind calculation model is used to determine the wind speed (using weather station data).
  4. The diffuse radiation formula is applied to calculate the diffuse radiation.
  5. The physiological equivalent temperature formulas are applied to calculate the final physiological equivalent temperature (PET).

Notes

  • Each date-time created in the Heat Overlay configuration wizard will be its own timestep.
  • In the DPRA report step description, the atmospheric temperature is only calculated once. However, the Atmospheric temperature formula used an hour of day input parameter and should therefore be performed each timestep.
  • We have not implemented an automatic translation to future KNMI WH-scenarios. However, since users can provide their own weather station data, it can be configured manually.
Heat Module
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Heat Module
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Group
Formulas
UHI • Temperatures • Diffuse radiation • PET
Calculation models
Foliage height • Sky view factor • Shade • Average vegetation and sky view factor
Related
Calculation models and formulas • Feature attributes • Model attributes • Result types


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