pTr_partition.m

% ---------------------------------- %
%  Potential transpiration partition %
% -----------------------------------%
function [Tr_p1, Tr_p2, Tr_p3] = pTr_partition(pEc, wa1, wa2, wa3, ...
    soilpar, pftpar, fwet, zm)
% ------- function input -------
% pEc    :  Potnetial Evaporation on canopy
% w      :  Initialized values for soil moisture
% pftpar :  PFT parameters
% ------- function output ------
% pTr_ly :  seperate potnetial Transpiration
% -------

b = soilpar(4);
D50 = pftpar(2);
D95 = pftpar(3);
c = -2.944/log(D95/D50);

theta_sat = soilpar(3);

r1 = (1 / (1 + (zm(1) / D50)^c));
r2 = (1 / (1 + (zm(2) / D50)^c)) - (1 / (1 + (zm(1) / D50)^c));
r3 = (1 / (1 + (zm(3) / D50)^c)) - (1 / (1 + (zm(2) / D50)^c));

% the maximum transpiration rate of each soil layer, Tr_p
% Get all avaliable water contents through root distribution
wr = r1 * (wa1 / theta_sat)^b + r2 * (wa2 / theta_sat)^b + r3 * ...
    (wa3 / theta_sat)^b;

% Root distribution adjusted by soil water content
beta1 = r1 * (wa1 / theta_sat)^b / wr;
beta2 = r2 * (wa2 / theta_sat)^b / wr;
beta3 = r3 * (wa3 / theta_sat)^b / wr;

% potentail transpiration rate for different layers
Tr_p1 = (1 - fwet) * beta1 * pEc;
Tr_p2 = (1 - fwet) * beta2 * pEc;
Tr_p3 = (1 - fwet) * beta3 * pEc;

end