UHI formula (Heat Overlay): Difference between revisions

From Tygron Support wiki
Jump to navigation Jump to search
Line 12: Line 12:
==Formula Decomposition==
==Formula Decomposition==
The formula has two parts, the factor and the temperature effect:<br>
The formula has two parts, the factor and the temperature effect:<br>
<math>UHI_{max} = [[#Factor|factor]] \cdot [[#Temperature effect|temperature_effect]]</math>
UHI_{max} = [[#Factor|factor]] \cdot [[#Temperature effect|temperature_effect]]
====Factor====
====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.
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.

Revision as of 13:15, 20 September 2019

The Urban heat island effect is calculated using the following formula:
where:

Formula Decomposition

The formula has two parts, the factor and the temperature effect:
UHI_{max} = factor \cdot 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