UHI formula (Heat Overlay): Difference between revisions
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where, | where, | ||
* | * <math>Q_{ql-avg}</math> is the [[Daily_avg_radiation_(Heat_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>T_{station}</math> is the hourly [[Hourly_temperature_(Heat_Overlay)|temperature]] measured at the station | ||
* | * <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) | ||
==See also== | ==See also== | ||
* [[Temperature_formulas_(Heat_Overlay)#Atmospheric Temperature formula|Atmospheric temperature formula]] | * [[Temperature_formulas_(Heat_Overlay)#Atmospheric Temperature formula|Atmospheric temperature formula]] | ||
{{Template:HeatOverlay_formula_nav}} | {{Template:HeatOverlay_formula_nav}} | ||
Revision as of 13:20, 20 September 2019
The Urban heat island effect is calculated using the following formula:
where:
![{\displaystyle UHI_{max}=(2-S_{vf}-F_{veg})\cdot {\sqrt[{4}]{\frac {S\cdot (T_{max}-T_{min})^{3}}{U}}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/29b572cdbb252ec0305752541e23969fd1caa508)
- 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:
UHImax = factor · 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.
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 gas constant for dry air. We use a value of 287.058 J/(kg·K)
See also
