UHI formula (Heat Overlay): Difference between revisions
Jump to navigation
Jump to search
No edit summary |
|||
| Line 34: | Line 34: | ||
* <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 celcius (°C) to kelvin (K) | |||
==See also== | ==See also== | ||
Revision as of 15:17, 13 February 2020
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:
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 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
