rootzone.py

# The Spatial Processes in HYdrology (SPHY) model:
# A spatially distributed hydrological model
# Copyright (C) 2013-2026  FutureWater
# Email: sphy@futurewater.nl
#
# Authors (alphabetical order):
# P. Droogers, J. Eekhout, A. Fernandez-Rodriguez, W. Immerzeel, S. Khanal, A. Lutz, T. Schults, G. Simons, W. Terink.
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.


# -Function to calculate surface runoff
def RootRunoff(self, pcr, rainfrac, rain):
    # -Infiltration excess surface runoff
    if self.InfilFLAG == 1:
        # -Infiltration capacity, scaled based on rootwater content and ksat and corrected for paved surface
        Infil_cap = (
            self.K_eff
            * self.RootKsat
            / 24
            * (1 + ((self.RootSat - self.RootWater) / self.RootSat)) ** self.Labda_Infil
        )

        # -Infiltration
        Infil_excess = pcr.ifthenelse(
            (self.Alpha * rain) > Infil_cap,
            rain - ((self.Alpha * rain - Infil_cap) ** 2) / (self.Alpha**2 * rain),
            rain,
        )
        Saturated_excess = self.RootSat - self.RootWater
        Infil = pcr.max(0, pcr.min(Infil_excess, Saturated_excess)) * (
            1 - self.pavedFrac
        )

        # -Surface runoff
        rootrunoff = rain - Infil

    # -Saturation excess surface runoff
    else:
        # -Assume infiltration capacity to be equal to saturated hydraulic conductivity
        Infil_cap = self.RootKsat

        # -Infiltration
        Infil = pcr.max(0, pcr.min(rain, Infil_cap, self.RootSat - self.RootWater))
        # -Runoff
        rootrunoff = pcr.ifthenelse(rainfrac > 0, rain - Infil, 0)

    return rootrunoff, Infil


# -Function to calculate rootzone drainage
def RootDrainage(pcr, rootwater, rootdrain, rootfield, rootsat, drainvel, rootTT):
    rootexcess = pcr.max(rootwater - rootfield, 0)
    rootexcessfrac = rootexcess / (rootsat - rootfield)
    rootlat = rootexcessfrac * drainvel
    rootdrainage = pcr.max(
        pcr.min(
            rootexcess,
            rootlat * (1 - pcr.exp(-1 / rootTT)) + rootdrain * pcr.exp(-1 / rootTT),
        ),
        0,
    )
    return rootdrainage


# -Function to calculate rootzone percolation
def RootPercolation(pcr, rootwater, subwater, rootfield, rootTT, subsat):
    rootexcess = pcr.max(rootwater - rootfield, 0)
    rootperc = rootexcess * (1 - pcr.exp(-1 / rootTT))
    rootperc = pcr.ifthenelse(
        subwater >= subsat, 0, pcr.min(subsat - subwater, rootperc)
    )
    rootperc = pcr.max(pcr.min(rootperc, rootexcess), 0)
    return rootperc


# -Function to calculate the right fraction between the two fluxes
def CalcFrac(pcr, rootwater, rootfield, rootdrain, rootperc):
    rootexcess = pcr.max(rootwater - rootfield, 0)
    frac = ((rootdrain + rootperc) - rootexcess) / (rootdrain + rootperc)
    rootdrain = rootdrain - (rootdrain * frac)
    rootperc = rootperc - (rootperc * frac)
    return rootdrain, rootperc