Monthly Pixel based Soil Moisture Balance

Data

Input Data

Variable Name	Shortname	Timestep	DataType	Mathematical symbol
Precipitation	p	monthly	netCDF	P
Actual Evapotranspiration	et	monthly	netCDF	ET_a
Interception	i	monthly	netCDF	I
Number of Rainy Days	nRD	monthly	netCDF	n
Reference Evapotranspiration	ret	monthly	netCDF	ET_r
WaPOR Land Cover Classification	lcc	yearly	netCDF	-
WA+ Landuse Categories	luwa	yearly	netCDF	-
Saturated Water Content	thetasat	static	netCDF	θ_sat

Look-up tables

Root depth look-up table (Yang et al., 2016)

WaPOR Land Cover Class	Root depth (mm)
Shrubland	370
Grassland	510
Cropland, rainfed	550
Cropland, irrigated or under water management	550
Cropland, fallow	550
Built-up	370
Bare/sparse vegetation	370
Permanent snow/ice	0
Water bodies	0
Temporary water bodies	0
Shrub or herbaceous cover, flooded	0
Tree cover: closed, evergreen needle-leaved	1800
Tree cover: closed, evergreen broad-leaved	3140
Tree cover: closed, deciduous broad-leaved	1070
Tree cover: closed, mixed type	2000
Tree cover: closed, unknown type	2000
Tree cover: open, evergreen needle-leaved	1800
Tree cover: open, evergreen broad-leaved	3140
Tree cover: open, deciduous needle-leaved	1070
Tree cover: open, deciduous broad-leaved	1070
Tree cover: open, mixed type	2000
Tree cover: open, unknown type	2000
Seawater	0

Consumed fraction per land use class

Landuse/Land cover class	Consumed fraction (f_consumed)
Natural land use classes	1.00
Rainfed crops	1.00
Irrigated crops	0.80

Intermediate variables

Variable Name	Shortname	Timestep	DataType	Mathematical Symbol
Rootdepth	rd	monthly	xarray.DataArray	z_root-zone
Maximum Rootzone soil moisture storage	smax	monthly	xarray.DataArray	S_max
Supply	qsupply	monthly	xarray.DataArray	Q_supply
Surface Runoff	sro	monthly	xarray.DataArray	Q_{sro_rain}
Incremental Surface Runoff	sro_incr	monthly	xarray.DataArray	Q_{sro_incr}
Percolation	perc	monthly	xarray.DataArray	Q_{perc_rain}
Incremental Percolation	perc_incr	monthly	xarray.DataArray	Q_{perc_incr}
Soil moisture storage	sm	monthly	xarray.DataArray	S

Output Data

Variable Name	Shortname	Timestep	DataType	Mathematical symbol
Rainfall ET	etrain	monthly	netCDF	ET_rain
Incremental ET	etincr	monthly	netCDF	ET_incr

Methodology

Step 0: Calculate Maximum Rootzone soil moisture storage

Look up root-depth (z_root-zone) based on Land Cover Classification

Then, maximum Rootzone soil moisture storage is calculated as:

S_max = θ_sat x z_root-zone

Step 1: Calculate surface runoff, percolation and temporary soil moisture

Step 2: Calculate soil moisture storage when there is no incremental ET

Step 3: Calculate soil moisture storage and supply when there is incremental ET

Step 4: Calculate incremental surface runoff and percolation when there is incremental ET

Reference

Yang, Y., Donohue, R.J., McVicar, T.R., 2016. Global estimation of effective plant rooting depth: Implications for hydrological modeling. Water Resour. Res. 52, 8260–8276. https://doi.org/10.1002/2016WR019392

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