Groundwater#

Groundwater storage and related fluxes are calculated based on section 4.5 of Müller Schmied et al 2021 [1].

groundwater.groundwater_balance(x, y, aridity_or_inlandsink, groundwater_storage, diffuse_gw_recharge, potential_net_abstraction_gw, daily_unsatisfied_pot_nas, gw_dis_coeff, prev_potential_water_withdrawal_sw_irri, prev_potential_consumptive_use_sw_irri, frac_irri_returnflow_to_gw, point_source_recharge=None)[source]#

Compute daily groundwater balance including storages and related fluxes.

Parameters:
xint

Latitude index of cell

yint

Longitude index of cell

aridiitystring

Compute groundwater for “Humid” or “Arid” region

groundwater_storagefloat

Daily groundwater storage, Unit: [km^3]

diffuse_gw_rechargefloat

Daily difuuse groundwater recharge, Unit: [km^3/day]

potential_net_abstraction_gwfloat

Potential net abstraction from groundwater, Unit: [km^3/day]

daily_unsatisfied_pot_nasfloat

Daily unsatisfied water use, Unit: [km^3/day]

gw_dis_coefffloat

Groundwater discharge coefficient (=0.01),Eqn 21 Müller Schmied et al. (2021), Unit: [1/day]

prev_potential_water_withdrawal_sw_irrifloat

Previous potential water withdrawal from surface water for irrigation, Unit: [km^3/day]

prev_potential_consumptive_use_sw_irri: float

Previous potential consumptive use from irrigation using surface water, Unit: [km^3/day]

point_source_rechargefloat

Sum of all point groundwater recharge from surface waterboides in arid regions, Unit: [km^3/day]

Returns:
groundwater_storagefloat

Updated daily groundwater storage, Unit: [km^3]

groundwater_dischargefloat

Updated daily groundwater discharge, Unit: [km^3/day]

actual_net_abstraction_gw: float

Actual Net abstraction from groundwater, Unit: [km^3/day]

Water balance#

Groundwater storage \(S_g\) \([m^3]\) is computed as

\[\frac{dS_g}{d_t} = {R}_{g} − {R}_{gl,res,w}− {Q}_{g} - {NA}_{g}\]

where \({R}_{g}\) is diffuse groundwater recharge from soil [\(m^3 {d}^{-1}\)]. \({R}_{gl,res,w}\) is point groundwater recharge from surface water bodies (lakes, reservoirs and wetlands) in (semi)arid areas [\(m^3 {d}^{-1}\)], \({Q}_{g}\) is groundwater discharge [\(m^3 {d}^{-1}\)] and \({NA}_{g}\) is net abstraction from groundwater [\(m^3 {d}^{-1}\)].

Inflows#

Diffuse groundwater recharge from soil \([m^3 {d}^{-1}]\) is the main inflow in humid cells and point groundwater recharge from surface water bodies (lakes, reservoirs and wetlands) \({R}_{gl,res,w}\) \([m^3 {d}^{-1}]\) is the main inflow in (semi)arid grid cells. \({R}_{gl,res,w}\) varies temporally with the area of the surface water body, which depends on the respective water storage.

Outflows#

Groundwater discharge, \(Q_g [m^3 {d}^{-1}]\) to surface waterbodies is an outflow which is computed as:

\[{Q}_{g} = {k}_{g} \times {S}_{g}\]

WaterGAP computes actual net abstraction from groundwater, \(NA_g [m^3 {d}^{-1}]\) from the potential net groundwater abstraction. The potential net abstraction from groundwater is computed from the Groundwater-Surface Water Use (GWSWUSE) model (see section 2 of Müller Schmied et al 2021 [1]). Details on the computation of the actual net abstaction groundwater can be found in the water abstractions section. net_abstractions:

Note

Groundwater storage is solved analytically for each timestep of one day to prevent numerical inaccuracies. This avoids the use of very small timesteps which will be computaionally expensive and hence lead to numerical problems.

Since \(R_g\) , \({R}_{gl,res,w}\) and \(NA_g\) are constant per each time step, they are grouped as one constant called Net recharge \((NR={R}_{g} − {R}_{gl,res,w} − {NA}_{g})\). The final balance euqation to solve is then:

\[\frac{dS_g}{d_t} = NR − {Q}_{g}\]

Analytical solution is given as:

\[S_g(t) = S_g(t-1) \times {exp}^{-k_g} + \frac{NR}{k_g} \times (1-{exp}^{-k_g})\]

References#