5.1. Precipitation Phase Partitioning

ADELM partitions total daily precipitation pr_mmday into rainfall rainfall_mmday and snowfall snowfall_mmday based on whether daily temperatures straddle the freeze-transition threshold freezing_point.

See also

model.processes.hydrology.calculate_precipitation_phase()

Coupling to other components

• Canopy Hydrology uses rainfall_mmday and snowfall_mmday.

• Snow Hydrology uses snowfall_mmday.

Assuming air temperature varies linearly between the daily minimum \(T_{\min}\) (ta_min_degC [degC; Driver: daily minimum near-surface air temperature]) and maximum \(T_{\max}\) (ta_max_degC [degC; Driver: daily maximum near-surface air temperature]), the fraction of the day above the freeze-transition threshold \(T_{\mathrm{freeze}}\) (freezing_point [default: 0 degC; Constant: temperature at which water freezes]) is \(f_{\mathrm{warm}}\):

(5.1.1)\[\begin{split}f_{\mathrm{warm}} = \begin{cases} 0 & T_{\max} \le T_{\mathrm{freeze}} \\ 1 & T_{\min} \ge T_{\mathrm{freeze}} \\ \dfrac{T_{\max} - T_{\mathrm{freeze}}}{T_{\max} - T_{\min}} & \text{otherwise} \end{cases}\end{split}\]

Rainfall and snowfall are then

(5.1.2)\[P_{\mathrm{rain}} = f_{\mathrm{warm}}\,P, \qquad P_{\mathrm{snow}} = (1 - f_{\mathrm{warm}})\,P\]

where \(P\) is pr_mmday [mm day-1; Driver: total daily precipitation as liquid-water equivalent].