UHI formula (Heat Overlay): Difference between revisions
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The S is calculated as followed: | The S is calculated as followed: | ||
S = | ρ<sub>air</sub> = p / R<sub>specific</sub> * (T<sub>station</sub> + 273.15) | ||
S = Q<sub>ql-avg</sub> / (C<sub>air</sub> * ρ<sub>air</sub>)<br> | |||
where, | where, | ||
* | * Q<sub>ql-avg</sub> is the daily average global radiation in W/m<sup>2</sup>hr<sup>-1</sup> | ||
* C<sub>air</sub> is the air heat capacity in J. We use a value of 1007.0. | |||
* T<sub>station</sub> is the temperature measured at the station | |||
* R<sub>specific</sub> 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) | |||
Revision as of 13:23, 11 September 2019
The Urban heat island effect is calculated using the following formula:
UHImax = ( 2 - Svf - Fveg ) * ( S * (Tmax-Tmin)3 / U )-4
where:
- Svf is the calculated average sky view factor;
- Fveg is the calculated average vegetation fraction;
- S is
Analysis
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 S is calculated as followed:
ρair = p / Rspecific * (Tstation + 273.15)
S = Qql-avg / (Cair * ρair)
where,
- Qql-avg is the daily average global radiation in W/m2hr-1
- Cair is the air heat capacity in J. We use a value of 1007.0.
- Tstation is the temperature measured at the station
- Rspecific is the gas constant for dry air. We use a value of 287.058 J/(kg·K)