| Variable | Description | Unit
|
| \(T\) | air temperature | °C
|
| \(T_{dew}\) | dew point temperature | °C
|
| \(H\) | air humidity | %
|
| \(P\) | rainfall | mm
|
| \(U\) | windspeed | m/s
|
| \(w\) | days since last rain
(or rain above threshold) | d
|
| \(rr\) | days with consecutive rain | d
|
| \(\Delta t\) | time increment | d
|
| \(\Delta{e}\) | vapor pressure deficit | kPa
|
| \(e_s\) | saturation vapor pressure | kPa
|
| \(e_a\) | actual vapor pressure | kPa
|
| \(p_{atm}\) | atmospheric pressure | kPa
|
| \( PET\) | potential evapotranspiration | mm/d
|
| \(r\) | soil water reserve | mm
|
| \(r_s\) | surface water reserve | mm
|
| \(EMC\) | equilibrium moisture content | %
|
| \(DF\) | drought factor | -
|
| \(N\) | daylight hours | hr
|
| \(D\) | weighted 24-hr average moisture condition | hr
|
| \(\omega\) | sunset hour angle | rad
|
| \(\delta\) | solar declination | rad
|
| \(\varphi\) | latitude | rad
|
| \(Cc\) | cloud cover | Okta
|
| \(J\) | day of the year (1..365/366) | -
|
| \(I\) | heat index | -
|
| \(R_n\) | net radiation | MJ⋅m-2⋅d-1
|
| \(R_a\) | daily extraterrestrial radiation | MJ⋅m-2⋅d-1
|
| \(R_s\) | solar radiation | MJ⋅m-2⋅d-1
|
| \(R_{so}\) | clear-sky solar radiation | MJ⋅m-2⋅d-1
|
| \(R_{ns}\) | net shortwave radiation | MJ⋅m-2⋅d-1
|
| \(R_{nl}\) | net longwave radiation | MJ⋅m-2⋅d-1
|
| \(\lambda\) | latent heat of vaporization | MJ/kg
|
| \(z\) | elevation | m a.s.l.
|
| \(d_r\) | inverse relative distance Earth-Sun | -
|
| \(\alpha\) | albedo or canopy reflection coefficient | -
|
| \(\Delta\) | slope of the saturation vapor pressure curve | kPa/°C
|
| \(Cc\) | cloud cover | eights
|
| \(ROS\) | rate of spread | m/h
|
| \(RSF\) | rate of spread factor | -
|
| \(WF\) | wind factor | -
|
| \(WRF\) | water reserve factor | -
|
| \(FH\) | false relative humidity | -
|
| \(FAF\) | fuel availability factor | -
|
| \(PC\) | phenological coefficient | -
|
Fire Weather Indices WIKI
