UHI formula (Heat Overlay): Difference between revisions

From Tygron Support wiki
Jump to navigation Jump to search
No edit summary
No edit summary
Line 1: Line 1:
__NOTOC__
__NOTOC__
The Urban heat island effect is calculated using the following formula:<br>
The Urban heat island effect is calculated using the following formula:<br>
UHI<sub>max</sub> = ( 2 - S<sub>vf</sub> - F<sub>veg</sub> ) · ( S · (T<sub>max</sub>-T<sub>min</sub>)<sup>3</sup> / U )<sup>-4</sup> <br>
<math>UHI_{max}</math> = ( 2 - S_{vf} - F_{veg} ) \cdot \root{\frac{ (S \cdot (T_{max}-T_{min})^3}{U}}{-4<}</math>
where:
where:
* S<sub>vf</sub> is the calculated [[Sky_view_avg_result_type_(Heat_Overlay)|average sky view factor]];
* S<sub>vf</sub> is the calculated [[Sky_view_avg_result_type_(Heat_Overlay)|average sky view factor]];

Revision as of 13:10, 20 September 2019

The Urban heat island effect is calculated using the following formula:
= ( 2 - S_{vf} - F_{veg} ) \cdot \root{\frac{ (S \cdot (T_{max}-T_{min})^3}{U}}{-4<}</math> where:

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:

Daily average global radiation

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/m2/hr
  • Cair is the air heat capacity in J. We use a value of 1007 J.
  • Tstation is the hourly temperature measured at the station
  • ρair is the calculated air density in kg/m3;
  • Rspecific is the gas constant for dry air. We use a value of 287.058 J/(kg·K)

See also