Edwin H. Sutanudjajaa, Rens van Beeka, Karen G. Villholthb, Aditya Soodc, Tingju Zhud

a Faculty of Geosciences, Utrecht Univ., The Netherlandsb IWMI, South Africa

c IWMI, Sri Lankad IFPRI, Washington DC

Progress and challenges in modelling globalgroundwater depletion - experience with

PCR-GLOBWB

25th May, 2015

1. How are constraints in groundwater availability and access influencing global groundwater depletion?

2. How is groundwater depletion influencing global food production?

3. How can better groundwater management improve food security?

Objective/Research questions

Groundwater depletion occurs when the rate of groundwater abstraction is greater than the rate of replenishment

Groundwater depletion: What is it?

S

R

D

Natural conditions

Averaged over long term, R=D and S is constant

S

R

D

Stable groundwater pumping

Qnet is equivalent to reduction in D and S

Qnet

S

R

D

Unsustainable condition

Qnet is greater than R, D reduces to 0 and S decreases continuosly

Qnet

19601963

19661969

19721975

19781981

19841987

19901993

19961999

0

50,000

100,000

150,000

200,000

250,000

300,000

Mm

3//y

ear

Total groundwater depletion

Source: Wada et al., 2012

Results from the PCR-GLOBWB model

Depletion = Abstraction - Recharge

Source:Shah et al., 2007

Gro

undw

ater

with

draw

al (c

ubic

km

per

yea

r)

in selected countries

at global scale

ProductionOf Total

(Rainfed & Irrigated)

Of Irrigated Of Irrigated by Groundwater

From GW abstraction 13.3% 44.4%

From GW depletion 4.3% 14.5% 32.6%

CROP PRODUCTION FROM GROUNDWATER AND GROUNDWATER DEPLETION

Results from Phase I of our work

PCR-GLOBWB model(Wada et al., 2012)

1. Non-renewable GW is implicitly assumed to be unlimited (same as in IGHM)

2. GW pumping is not constrained by socio-economic and technical factors.

Shortcomings of PCR-GLOBWB model

1st constraint: Aquifer volume

Estimate of aquifer thickness at 30 arc-min resolution

2nd constraint: Pumping capacity

Regional-scale groundwater abstraction limit (109 m3/yr) for 2005

From IMPACT

2nd constraint: Pumping capacity

Global groundwater abstraction limit for the period 1960-2015

River flow stations for calibration and validation

Locations of GRDC discharge stations used in this study. Black dots represent stations selected for calibration and yellow dots represent stations selected for validation.

Recursive filter method by Nathan and McMahon (1990):

qd = β qd-1+ (1+ β) (Qd - Qd-1)/2 separated surface flow

qb = Qd - qd separated baseflow

Baseflow separation

Calibration parameters

fD: Pre-factor for degree day factor

fW: Pre-factor for soil water capacities

fK: Pre-factor for upper soil sat. hydraulic conductivity

fJ: Pre-factor for groundwater recession coefficient

Calibration against total flows (Orinoco)

Improvement observed

Results:

Calibration against total flows (Congo)

No improvement observed

Results: Calibration against total flows (Congo)

Calibration against baseflows (Orinoco)

Improvement observed

Results:

Calibration against baseflows (Ob)

No improvement observed

Results:

1. Run without constraints2. Run with limited non-renewable GW3. Run with limited non-renewable GW

and limited pumping capacity4. Run 3., but calibrating parameters

Approach to simulations

Run 1Results:

km3 y

ear−1

Total depletion: 375 km3 yr-1

2001-2008

Adding constraintsResults:

km3 y

ear−1

Run 1 Run 2

Run 3

Total depletion: 285 km3 yr-1

2001-2008 Total depletion: 375 km3 yr-1

2001-2008

Total depletion: 146 km3 yr-1

2001-2008

Run 4(Calib)

Total depletion: 183 km3 yr-1

2001-2008

Global Groundwater ScenariosStarting Point: IPCC’s Shared Socioeconomic Pathways (SSPs)

Managed Aquifer Recharge (MAR)

Implemented in scenarios emphasizing sustainability/adaptation

Pumping control Implemented in scenarios emphasizing sustainability/mitigation

New GW developmentImplemented to various degree, dep. on scenario

Trade/virtual water Implemented in scenarios with good global/international institutions

Water productivity Improved in scenarios emphasizing sustainability/mitigation

Issues/Interventions considered

SSP5 Pumping in depleted regions is not controlled MAR/UTFI is implemented on a large scale,

mostly to control extreme flooding Balanced new GW dev. in potential regions to

adapt to CC Trade/virtuous virtual water flows

constrained by dominant economic development imperatives

Water productivity from GW (and SW) not improved

SSP3 (worst case) Pumping in depleted regions is not controlled MAR is not practised Unbalanced new GW dev. in potential

regions Trade/virtuous virtual water flows

constrained by dominant self-sufficiency strategies

Water productivity from GW (and SW) not improved

SSP1 Pumping in depleted regions is controlled

through regulations and incentive-based methods

MAR is implemented on a large scale Balanced new GW dev. in potential regions Trade is deliberately used to control GW

depletion (virtuous virtual water flows) Water productivity from GW (and SW)

improved

SSP4 Pumping in depleted regions is controlled

through effective energy policies MAR is not implemented Unbalanced/unequal new GW dev. in

potential regions, e.g. for biofuels Trade is deliberately used to control GW

depletion (virtuous virtual water flows), but not benefitting the smallholders

Water productivity from GW (and SW) improved to save energy in commercial farming

Scenario Storyline

1. Availability and access constraints to GW are critical to consider in future food security scenarios

2. Adding constraints and calibration improved the model’s handling of groundwater.

3. This compares well to previous estimates (145+/-39 km3 yr-1, Konikow (2011)).

4. Once included in IMPACT, global scenarios for different SSPs will be created and analyzed

5. Focus on country and regional level studies.

Conclusions

THANK YOU !!