UHI formula (Heat Stress Overlay): Difference between revisions
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where: | where: | ||
* S<sub>vf</sub> is the calculated [[Sky_view_avg_result_type_( | * S<sub>vf</sub> is the calculated [[Sky_view_avg_result_type_(Heat Stress Overlay)|average sky view factor]]; | ||
* F<sub>veg</sub> is the calculated [[Vegetation_avg_result_type_( | * F<sub>veg</sub> is the calculated [[Vegetation_avg_result_type_(Heat Stress Overlay)|average vegetation fraction]]; | ||
* S is the calculated [[#Daily average global radiation|daily average global radiation]] in K m/s | * S is the calculated [[#Daily average global radiation|daily average global radiation]] in K m/s | ||
* T<sub>max</sub> is the [[Daily_temperature_max_( | * T<sub>max</sub> is the [[Daily_temperature_max_(Heat Stress Overlay)|maximum temperature]] measured at a weather station between 8 AM and 7 AM the next day. | ||
* T<sub>min</sub> is the [[Daily_temperature_min_( | * T<sub>min</sub> is the [[Daily_temperature_min_(Heat Stress Overlay)|minimum temperature]] measured at a weather station between 8 AM and 7 AM the next day. | ||
* U is the [[Daily_avg_wind_speed_( | * U is the [[Daily_avg_wind_speed_(Heat Stress Overlay)|daily average wind speed]] measured at 10 meters above ground at a weather station. | ||
==Formula Decomposition== | ==Formula Decomposition== | ||
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where, | where, | ||
* <math>Q_{ql-avg}</math> is the [[Daily_avg_radiation_( | * <math>Q_{ql-avg}</math> is the [[Daily_avg_radiation_(Heat Stress Overlay)|daily average global radiation]] in W/m<sup>2</sup>/hr | ||
* <math>C_{air}</math> is the air heat capacity in J. We use a value of 1007 J. | * <math>C_{air}</math> is the air heat capacity in J. We use a value of 1007 J. | ||
* <math>T_{station}</math> is the hourly [[Hourly_temperature_( | * <math>T_{station}</math> is the hourly [[Hourly_temperature_(Heat Stress Overlay)|temperature]] measured at the station | ||
* <math>\rho_{air}</math> is the calculated air density in kg/m<sup>3</sup>; | * <math>\rho_{air}</math> is the calculated air density in kg/m<sup>3</sup>; | ||
* <math>R_{specific}</math> is the [https://en.wikipedia.org/wiki/Specific_gas_constant | * <math>R_{specific}</math> is the [https://en.wikipedia.org/wiki/Specific_gas_constant specific gas constant] for dry air. We use a value of 287.058 J/(kg·K) | ||
* <math>273.15</math> converts the used temperature from celcius (°C) to kelvin (K) | * <math>273.15</math> converts the used temperature from celcius (°C) to kelvin (K) | ||
{{article end | {{article end | ||
|seealso= | |seealso= | ||
* [[Temperature_formulas_( | * [[Temperature_formulas_(Heat Stress Overlay)#Atmospheric Temperature formula|Atmospheric temperature formula]] | ||
|references= | |references= | ||
<references> | <references> | ||
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|page= | |page= | ||
|source= | |source= | ||
|link= | |link=https://gert-jan.steeneveld.wur.nl/Theeuwes_JOC_2016.pdf | ||
|lastvisit= | |lastvisit=2026-02-25 | ||
}} | }} | ||
</references> | </references> | ||
}} | }} | ||
{{HeatOverlay_formula_nav}} | {{HeatOverlay_formula_nav}} | ||
Latest revision as of 11:42, 13 April 2026
The Urban heat island effect is calculated[1] using the following formula:
where:
- Svf is the calculated average sky view factor;
- Fveg is the calculated average vegetation fraction;
- S is the calculated daily average global radiation in K m/s
- Tmax is the maximum temperature measured at a weather station between 8 AM and 7 AM the next day.
- Tmin is the minimum temperature measured at a weather station between 8 AM and 7 AM the next day.
- U is the daily average wind speed measured at 10 meters above ground at a weather station.
Formula Decomposition
The formula has two parts, the factor and the temperature effect:
Factor
The factor is influenced by the sky view factor and the vegetation fraction, both ranging from 0 to 1. When both are low, i.e. barely any sky and no vegetation, the factor is near 2. When both are high, i.e. no surrounding buildings and a lot of vegetation, the factor is near 0. In that case, the resulting heat island effect will be low as well.
Temperature effect
The Urban heat island temperature effect is calculated as:
- the daily average global radiation S,
- the maximum-minimum temperature difference ΔT
- the daily average wind speed, measured at 10m above ground.
Daily average global radiation
The S is calculated as followed:
where,
- is the daily average global radiation in W/m2/hr
- is the air heat capacity in J. We use a value of 1007 J.
- is the hourly temperature measured at the station
- is the calculated air density in kg/m3;
- is the specific gas constant for dry air. We use a value of 287.058 J/(kg·K)
- converts the used temperature from celcius (°C) to kelvin (K)
See also
References
- ↑ A diagnostic equation for the daily maximum urban heat island effect for cities in northwestern Europe ∙ N.E. Theeuwes et al. ∙ Found at: https://gert-jan.steeneveld.wur.nl/Theeuwes_JOC_2016.pdf ∙ (last visited: 2026-02-25)
