UHI formula (Heat Overlay)

From Tygron Support wiki
Jump to navigation Jump to search

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)