non-sustainable groundwater sustaining irrigation gwf … · wherever access to surface water is...

Suggested Citation: Wada, Y. 2012, ‘Non-‐sustainable groundwater sustaining irrigation’, GWF Discussion Paper 1205, Global Water Forum, Canberra, Australia. Available online at: http://www.globalwaterforum.org/2012/02/13/non-‐sustainable-‐groundwater-‐sustaining-‐irrigation/

Non-‐sustainable groundwater sustaining irrigation

Yoshihide Wada Utrecht University, The Netherlands

Discussion Paper 1205 February 2012

This article looks at the use of non-‐renewable groundwater in the production of irrigated crops. Using a global hydrological model to simulate water demand for irrigated crops, blue water, green water, and groundwater recharge rates, together with groundwater extraction data from the IGRAC, the author finds that irrigation is increasingly being supported by non-‐sustainable water sources.

The Global Water Forum publishes a series of discussion papers to share the insights and knowledge contained within our online articles. The articles are contributed by experts in the field and provide original academic research; unique, informed insights and arguments; evaluations of water policies and projects; as well as concise overviews and explanations of complex topics. We encourage our readers to engage in discussion with our contributing authors through the GWF website.

Keywords: Irrigation; blue water; green water; non-‐renewable groundwater; groundwater depletion.

Irrigated crops play a vital role in securing

global food production. Approximately 40% of

food globally is produced from irrigated crops,

sustaining the livelihood of billions of people1.

In order to sustain irrigation, large amounts of

water are withdrawn from rivers, lakes,

reservoirs, and groundwater, together making

up about 70% of global water withdrawals. In

regions overlying productive aquifers,

wherever access to surface water is limited,

groundwater is the main source of irrigation

water.

Groundwater also serves as a temporary

source of irrigation water if surface water is

insufficient to satisfy demand during the dry

season or during dry years. Importantly, when

groundwater abstraction exceeds the recharge

rate over extensive areas for prolonged

periods, persistent groundwater depletion

occurs leading to falling groundwater levels.

In such cases, fossil groundwater, not being an

active part of the current hydrological cycle, is

used as an additional, albeit non-renewable,

source of irrigation water.


Regional studies using the GRACE (Gravity

Recovery And Climate Experiment) satellite

observation revealed that considerable

amounts of non-renewable groundwater

resources are being abstracted in North East

India, North West Pakistan, and California’s

Central Valley, most of which is used for

irrigation2,3. Further studies also reported

depleting groundwater resources due to

irrigation in the High Plains (Ogallala) aquifer,

USA4,5. Yet, up to now, no global studies have

explicitly identified which part of irrigation

water demand is currently met from non-

renewable groundwater abstraction. Assessing

this contribution is important because it

pinpoints areas where irrigation and thus food

production is sustained by a non-sustainable

water resource.

To estimate this contribution, we used the

global hydrological model PCR-GLOBWB

(PCR-GLOBal Water Balance) to simulate

crop water demand for irrigated crops,

available surface water (i.e., blue water), soil

water (i.e., green water), and groundwater

recharge for the period 1960-2000 at a spatial

resolution of 0.5° by 0.5° (i.e., 50 km by 50

km at the equator).

To estimate groundwater abstraction, we

obtained groundwater abstraction rates per

country and groundwater regions where major

aquifers are present from the IGRAC

(International Groundwater Resources

Assessment Centre). We then downscaled

country groundwater abstraction rates to a 0.5°

grid resolution by calculating deficits of the

simulated surface water availability over

estimated total water demand as a proxy.

Non-renewable groundwater abstraction was

subsequently calculated by subtracting the

simulated groundwater recharge from the

gridded groundwater abstraction. Negative

values indicate grid cells with sufficient

groundwater recharge and positive values

denote grid cells where non-renewable

groundwater is abstracted. We used the

fraction of irrigation water demand over total

water demand to estimate non-renewable

groundwater abstraction for irrigation.

Results show that global water use for

irrigated crops amounts to 2,510 km3 yr-1, of

which 47% (1,172 km3 yr-1) and 53% (1,338

km3 yr-1) are supplied from green water and

blue water respectively for the year 2000.

Surface water contributes 63% or 844 km3 yr-

1 to irrigation water, whilst non-renewable

groundwater contributes 18% or 234 km3 yr-1.

The remaining 19% or 260 km3 yr-1 is

supplied from non-local water resources such

as desalination and diverting water ways (i.e.,

aqueducts). We estimate that about 85% of

global non-renewable groundwater


abstraction (275 km3 yr-1) is used for

irrigation.

Figure 1. Current contribution per water

resource to water used for irrigated crops for

major groundwater users. Source: Wada

(2012).

When looking at country estimates (see Figure

1), India uses the largest amount of non-

renewable groundwater for irrigation (19% or

68 km3 yr-1). Due to scarce rainfall and a

semi-arid climate, 80% or 146 km3 yr-1 of

crop water demand in Pakistan is satisfied by

irrigation. While a major part of irrigation

water is taken from the Indus river, non-

renewable groundwater contributes 24% to

irrigation and amounts to 35 km3 yr-1, the

second largest volume after India.

In the USA and Mexico, around 20% of

irrigation water comes from non-renewable

groundwater. In Iran and Saudi Arabia, where

rainfall and surface freshwater are extremely

scarce, non-renewable groundwater provides

the largest contribution to irrigation water, 40%

and 77%, respectively.

Large fractions of non-renewable groundwater

abstraction over irrigation water demand are

observed predominantly in arid regions such

as the Middle East. Non-renewable

groundwater supplies more than half of the

irrigation water in Saudi Arabia, Qatar, Libya,

and the UAE. In these countries, where almost

all the available blue water is used for

irrigation, additional abstraction of non-

renewable groundwater will result in further

depletion of groundwater resources.

Figure 2. Past trends in the contribution per

water resource to the global crop water

demand. Source: Wada (2012)

We also reconstructed past trends of different

water resources contributing to irrigated crops.

Figure 2 shows that crop water demand more

than doubled from 1,217 to 2,510 km3 yr-1

over the period 1960-2000. For the year 1960,

green water contributed 48% or 589 km3 yr-1

to global crop water demand, resulting in an

irrigation water demand of 628 km3 yr-1. Blue

water and non-renewable groundwater


supplied 73% or 457 km3 yr-1 and 12% or 75

km3 yr-1 of the irrigation water respectively,

leaving 15% or 96 km3 yr-1 from non-local

water resources.

During the 1960-2000 period, global

irrigation water demand more than doubled to

1,338 km3 yr-1 as a result of expansion in

irrigated areas to support growing food

demand. The amount of blue water

contributing to global irrigation water demand

also increased to 844 km3 yr-1 but its share

decreased to 63% for the year 2000. However,

the amount and share of non-renewable

groundwater rose to 234 km3 yr-1 and close to

20% respectively. These results suggest that

available blue water resources have become

extensively exploited for irrigation.

Even though large numbers of reservoirs were

constructed to supply water to irrigation, the

increase in their storage capacities has been

tapering off since the 1990s. Consequently,

the contribution of non-renewable

groundwater abstraction to meet irrigation

water demand has been increasing rapidly,

resulting in an increasing dependency on non-

renewable groundwater for irrigation in recent

years.

In conclusion, irrigation is more and more

sustained by an unsustainable water source

over time, which increases the depletion of

groundwater resources. The unsustainable use

of groundwater for irrigation is an important

issue not only for the countries with intensive

groundwater use, but also for the world at

large since international trade directly links

food production in one country to

consumption in another. This study gives

further evidence to the scale of the issue and

its growing trend. It is therefore important to

invest further political, institutional, and

economic efforts to limit the overdraft, yet

also to find adaptive responses that do not

reduce current food productivity.

References

1. Abdullah, K. B. (2006), ‘Use of water and land for food security and environmental sustainability’, Irrigation and Drainage, Vol. 55, pp. 219–222, doi: 10.1002/ird.254.

2. Rodell, M., I. Velicogna, and J. S. Famiglietti (2009), ‘Satellite-based estimates of groundwater depletion in India’, Nature, Vol. 460, pp. 999–1002, doi:10.1038/nature08238. 3. Famiglietti, J. S. et al. (2011), ‘Satellites measure recent rates of groundwater depletion in California’s Central Valley’, Geophysical Research Letters, Vol. 38, L03403, doi:10.1029/2010GL046442. 4. McGuire, V. L. (2009), Water level changes in the High Plains Aquifer, Predevelopment to 2007, 2005–06, and 2006–2007, U.S. Geological Survey Scientific Investigations Report 2009-5019. Available at <http://pubs.usgs.gov/sir/2009/5019/>. 5. Scanlon, B. R., R. C. Reedy and J. B. Gates (2010), ‘Effects of irrigated agroecosystems: 1. Quantity of soil water and groundwater in the southern High Plains, Texas’, Water Resources Research, Vol. 46, W09537, doi:10.1029/2009WR008427.


About the author(s)

Yoshihide Wada is a PhD researcher at the Department of Physical Geography, Faculty of Geosciences, Utrecht University, the Netherlands. His PhD projects include estimating global water demand and water availability by using a global hydrological model PCR-GLOBWB. His work also includes estimating and projecting global water scarcity and the sustainability of global groundwater resources. The article is based on an original piece of research published in Water Resources Research titled, ‘Non-sustainable groundwater sustaining irrigation’.

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