UHI formula (Heat Stress Overlay): Difference between revisions
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=====Daily average global radiation===== | =====Daily average global radiation===== | ||
The S is calculated as followed:<br> | The S is calculated as followed:<br> | ||
<math>\rho_{air} = p | <math>\rho_{air} = \frac{p}{R_{specific} \cdot (T_{station} + 273.15)}</math> | ||
<math>S = \frac{Q_{ql-avg}}{C_{air} \cdot \rho_{air}}</math> | <math>S = \frac{Q_{ql-avg}}{C_{air} \cdot \rho_{air}}</math> | ||
where, | where, | ||
* <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>p</math> is the atmospheric pressure, also known as air pressure, with a value of 101325 Pa. | ||
* <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_(Heat Stress Overlay)|temperature]] measured at the station | * <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 specific gas constant] for dry air. We use a value of 287.058 J/(kg·K) | * <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 | * <math>273.15</math> converts the used temperature from degrees Celsius (°C) to Kelvin (K). | ||
{{article end | {{article end | ||
Latest revision as of 08:57, 9 October 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 atmospheric pressure, also known as air pressure, with a value of 101325 Pa.
- 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 degrees Celsius (°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)
