waterbalance: Internal function for the water balance model

In ilmenichetti/reclim: calculating climate scaling factors for the ICBM SOC modell

Internal function for the water balance model

Description

Internal function for the water balance model

Usage

waterbalance(twilt, tfield, precipitation, GAI, date, ET0, L)

Arguments

twilt	wilting point (0 to 1)
tfield	field capacity (0 to 1)
precipitation	daily precipitations (mm)
GAI	green area index daily values
date	date vector
ET0	Evapotranspiration (calculated based on PET and GAI)
L	soil depth (mm)

Details

The formulas come mainly from Allen et al., 1998 https://www.fao.org/3/x0490e/x0490e00.htm and it is used to simulate the soil water balance. The calculation is done through multiple steps, iterated for each timestep:

Step 1: Soil water W is initialized assuming saturation, based on the depth L and volumetric capacity

W[1] = \Theta_f \cdot L

Step 2: The single crop coefficient Kc is calculated based on GAI

K_c=1.3-0.5 \cdot exp(-0.17 \cdot GAI)

Step 3: calculation of crop evapotranspiration (ETc) under standard condition

ET_c=ET_0 \cdot K_c

Step 4: the intercepted water It is calculated based on crop ET, GAI and precipitation P

It=min(P,ET_c,0.2 \cdot GAI)

Step 5: potential evapotraspiration is calculated

E_{pot}=(ET_c-It)

Step 6: Calculation of the percolation. Water (W_b, water bypass) is lost when above field capacity, but allowing saturation for one day

W_b = max(0, W-(\Theta_f \cdot L))

Step 7: Soil evaporation reduction coefficient

Kr=(1-(0.95 \cdot tfield-\Theta)/(0.95 \cdot tfield-\alpha \cdot twilt))^2

Subsequent conditions are applied so that Kr cannot be above one, and the values before the minimum Kr are also zero. Step 8: Actual evapotraspiration is calculated

E_{act}=E_{pot} \cdot Kr

Step 9: The water balance is calculated (stepwise)

W[i+1]=W[i]+P[i]-E_{act}[i]-It-W_b[i]

Value

The function returns a data frame with water balance and date (days)

Author(s)

Lorenzo Menichetti [e-mail]

ilmenichetti/reclim documentation built on Sept. 23, 2023, 7:15 p.m.