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4610.0 - Water Account, Australia, 2011–12 Quality Declaration 
Previous ISSUE Released at 11:30 AM (CANBERRA TIME) 13/11/2013   
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This document was added 11/22/2013.



FEATURE ARTICLE 2: EXPERIMENTAL ESTIMATES OF SOIL WATER USE IN AUSTRALIA


1.0 INTRODUCTION

1. The ABS Water Account Australia (WAA) (cat. no. 4610.0) collects a wide range of information on water use from standing stocks (for example rivers, groundwater and dams). Measurement of soil water is recommended in international water accounting standards but is not currently included in the WAA. Soil water resources are a considerable water resource (over 325,000 GL in 2011-12, see Figure 1) and its use has impacts on managing run-off into standing water supplies, percolation into groundwater resources and loss of biodiversity for native species. This article describes a methodology and preliminary results for measuring the use of soil water in the economy.

Figure 1 - Supply of soil water into the Australian economy
Graph: Figure 1 – Supply of soil water into the Australian economy


2. Soil water estimates are proposed to be introduced to the 2012-13 WAA which will be published in late 2014. The methods and results described in this article are considered to be experimental. Discussion, comments or suggestions on the methodology and results are welcome and can be sent to <environment@abs.gov.au>.


1.1 Definitions

3. Soil water is described in both the System of Environmental-Economic Accounts - Water (SEEA-W) and the 2012 version of the System of Environmental-Economic Accounts (SEEA 2012). This method prefers the SEEA 2012 framework for measuring soil water abstraction which excludes evaporation and any water retained in the soil. Evaporation and water retained in soil may be measured in future extensions to the WAA.

4. Soil water is defined in SEEA-Water as:

“Soil water consists of water suspended in the uppermost belt of soil, or in the zone of aeration near the ground surface, that can be discharged into the atmosphere by evapotranspiration.” (para. 6.17)

5. Soil water estimates are defined in SEEA 2012 as:

“Abstraction of soil water refers to the uptake of water by plants and is equal to the amount of water transpired by plants plus the amount of water that is embodied in the harvested product” (SEEA 2012 para. 3.198)

6. There are three estimates that measure soil water abstraction and use:
  • Soil water (source of abstracted water);
  • Water incorporated into products; and
  • Water transpired.

7. Soil water estimates appear in physical supply and use tables as a source of abstracted water from the environment and as a use of the sources of abstracted water by industry and households. Water transpiration from soil water and water incorporated into products are supplied by industry and households. In this model, transpired soil water flows to the environment and reflects the quantity of water no longer available for use by the economy. Water incorporated into products is defined by the accumulated water in the economy embodied in harvested plant material. Water embodied in exports and imports are not included in this methodology.

8. There are two potential sources of double counting in these results, but they have a minor impact on estimates. Hay and silage consumed by livestock should be offset in the pasture component of the model, but it is not known if the hay and silage is consumed in the same financial year or in different financial years. Hay and silage soil water abstraction is approximately 2% of total soil water abstracted by the activities of grazing in 2011-12. The other component of potential double counting in the WAA are irrigation on crops and pasture. Irrigation is used to supply water to productive activities where there is a lack of rainfall or rainfall does not occur at times suitable for plant growth. Irrigation estimates will be netted out when soil water estimates are incorporated into the water flow tables. Irrigation accounted for 2% of soil water abstraction in 2011-12.
2.0 METHODOLOGY FOR ESTIMATING SOIL WATER USE, WATER INCORPORATED INTO PRODUCTS AND WATER TRANSPIRED TO THE ENVIRONMENT

9. Water Use Efficiency (WUE) defines the efficiency with which water - rainfall or irrigation - is converted through a farming system into a saleable commodity, for example, grain, meat or fibre (http://www.csiro.au/en/Organisation-Structure/Divisions/Ecosystem-Sciences/Water-Use-Efficiency.aspx, extracted June 2013). One of the core components of modelling soil water is plant material extracting water from the environment. Evapotranspiration describes a plant's need for water as a part of the growth process. In this process, water is taken up from the environment, stored and used to combine with other bio-chemical processes for growth. These processes have been described in many scientific studies and generally use a coefficient (WUE) based on yield of plant material, the water applied and the area used for planting. For each agricultural or forestry commodity the coefficient used (WUE) has the characteristics:

10. The French & Schultz article discusses the minimum soil moisture requirement for crop plants (wheat in the article's case study) to establish themselves. The WUE formula assumes that there is sufficient water moisture content in the soil to allow transpiration and plants to establish. In their case study plants established at about 100 mm of rainfall (or about 1 ML per hectare), though other studies have shown that this base moisture level for crops can vary between 80 and 140 mm.

11. The coefficient is an extremely useful measure for calculating soil water use. With the assumption that there is sufficient soil moisture content before farmers decide to plant means that the WUE coefficient can be used to calculate the soil water required for a particular plant:
      Soil water abstracted (Litres) = final yield (kg of plant species harvested) x (1 WUE) x total area planted (m2)

12. For some plants (for example in plantations and horticulture) the water use efficiency coefficient is not widely available. This means a slight change in context and the formula for water use is needed to align for own account water use (per year for horticulture and per tree for orchards).
      Soil water abstracted = annual soil water uptake (mm/yr) x area planted (m2)

      Note that area planted for orchards is calculated by the total number of trees divided by number of trees per hectare.

13. Measurement of water incorporated into products is a simple calculation once the weight of any harvested material is known. Water incorporated into products can be calculated through the formula:
      water incorporated in product (Litres) = weight of product (kg) x moisture content of product

14. As water transpired is the residual flows of water after growth processes have taken place then its calculation can be the net of soil water and the water stored in the products. Water transpired back to the environment is calculated through the identity recommended in SEEA 2012:
      Soil water abstracted = water incorporated in product + water transpired.

15. Example
    A 100 hectare (1 000 000 metres squared) plot of sown wheat has a yield of 1 000 kg. The Water Use Efficiency coefficient for wheat in the area is 18 kg/{mm x ha}. Note that one mm per metre squared is equal to one litre.

      i.e. Soil water abstracted = 1 000 x 1/18 x 1 000 000 = 55 555 555 L (or over 55 ML)

    The moisture content of wheat is approximately 10g water per 100g wheat.


      i.e. Water incorporated into plants = 1 000 kg x 10 g 100 g = 100 L

    Hence,
      Water transpired = (55 555 555 - 100) L = 55 555 455 L (or over 55 ML)


2.1 Data sources

16. Soil water use estimates are derived from the sources detailed in Table 1. These named sources need a small degree of transformation to make them suitable for the estimation process. Some of the detailed WUE coefficients are determined using assumptions based on neighbouring states or assuming that the water use coefficient is consistent across the state. While there are likely to be some differences, the contribution of those products impacted by the assumption were found to be quite small (less than 1% of the total estimate). More recent estimates of water use by horticultural species (vegetables, fruits and nuts, other plantations) would be useful but their contribution to total soil water is quite small (less than 1%) and any changes are likely to be insignificant.
Table 1 - Data sources used in soil water use estimation

Key data source
Commodity GroupWeight Area WUE

Broadacre crops Agricultural commodity statistics (ABS) Agricultural commodity statistics (ABS) Scientific case studies
Other crops Agricultural commodity statistics (ABS) Agricultural commodity statistics (ABS) Scientific case studies
Vegetables Agricultural commodity statistics (ABS) Agricultural commodity statistics (ABS) Food and Agriculture Organisation (FAO)
Fruits and nuts Agricultural commodity statistics (ABS) Modelled Food and Agriculture Organisation (FAO)
Other plantations Agricultural commodity statistics (ABS) Agricultural commodity statistics (ABS) Food and Agriculture Organisation (FAO)
Pasture Modelled Agricultural commodity statistics (ABS) + modelled Scientific case studies
Forests Modelled National Plantation Inventory (ABARES) Scientific case studies
Urban green space Modelled Modelled from ACLUMP (ABARES) Turf watering Australia and native pasture coefficients




2.2 Transformations and assumptions

17. The two main transformations convert estimates of weight and area to standard units of kilograms for weight and hectares for area. Water use efficiency was typically measured in kg/mm.ha, except for annual water use for horticultural species which were measured in mm/year. These calculations use the fact that one mm per metre squared is equivalent to one litre of water (or 1 mm translates to 10 000 L over a hectare).

18. The area for fruits and nuts was modelled based on the number of live trees at the end of the period by the average number of trees for that particular species. The average number of trees per hectare is available on state and territory primary industry websites.

19. Pasture weight estimates were considered to be the harvested pasture by livestock on that land. Native pasture and modified pasture have widely differing characteristics. Modified pasture yields on average about 30 kg per hectare of plant material for every 5 kg of plant material per hectare of native pasture. The amount of modified pasture used is small (Figure 2) in comparison to native pasture. Cattle and sheep were considered to be the primary source of harvesting livestock for pasture. Their consumption rates were assumed to be consistent across Australia. The model used approximated consumption by cattle to be 16 kg per day and consumption by sheep to be 2.5 kg per day. These values are consistent with Eurostat's measure of biomass consumed by livestock for their material flow accounts. The slightly elevated intake reflects the drier conditions and quality of grass stocks in Australia compared to Europe.

20. Pasture area estimates were modelled for some years using total pasture as a constraining value or interpolated when data were missing. Figure 2 demonstrates the effects of modelling.

Figure 2 - Area of native and modified pasture, Australia
Graph: Figure 2 – Area of native and modified pasture, Australia

21. Forest water abstraction is based on growth of trees and can be estimated using a coefficient of growth per hectare and densities (kg/m3) for particular forest species groups (broadleaf and coniferous). The key component needed to model forest soil water abstraction is the increase in weight in plantations for the reference year. Forest weight needs to be modelled due to the limitations of existing data for plantations. No growth values are calculated for native forests as these are considered to be outside of the economy until harvested.

22. Grass and other plant material harvested in urban and rural residential land uses was modelled. Harvesting activities in urban and rural residential generally describe the removal of organic material from green spaces which is predominantly from mowing lawns and other fields. These harvesting activities in urban and rural residential regions are equivalent to own account production of plant material and should be included in the economy. The weight was calculated in two ways. Weights of removed material from urban land use types was based on watering rates by State and expected material produced from lawn mowing activity approximated by hay and silage yields seen on modified pasture (that is about 30 kg per hectare per year). Rural residential was engineered from the water use coefficient and applying a standard yield per hectare based on the native grass production. Values for soil water abstraction by urban gardens was not included in these estimates. Ovals and parklands were considered to be in the estimate as the area used to calculate soil water abstraction included green space in urban environments.

23. Area for urban and rural residential land use is modelled based on the Australian Collaborative Land Use and Management Program (ACLUMP) and movements in household estimates from Household and Family Projections, Australia 2006 to 2031 (ABS cat. no 3236.0). It was assumed that capital city household growth rates were sufficient for urban land use and the balance of state household growth rates were sufficient for rural residential land uses.

24. Estimates of gross soil water include water applied as irrigation for agricultural, household and parkland management activities. These need to be netted out before they are applied to supply use tables due to the risk of double counting abstraction.


2.3 Water incorporated into products

25. Water incorporated into products in these estimates are the moisture remaining in plant material after it is harvested. The moisture content varies widely between plant species. For example some species of lettuce are 90% water whereas wheat is only around 10%. These moisture contents are not published here but are available from food content websites such as the Australian Food Standards site (http:\\www.foodstandards.gov.au).

26. Water incorporated in products is a simple transformation:
      Water incorporated in products = weight of product x moisture content.


2.4 Water transpiration

27. Water transpired is calculated as a residual to the calculation of soil water and water incorporated into products. The soil water identity recommended in SEEA Central Framework (SEEA-CF) is the most efficient way of producing transpiration data.

28. Water transpiration is calculated using the identity:
      Soil water = Water incorporated in products + water transpired


3.0 RESULTS

3.1 Soil water abstraction

29. Gross soil water abstraction describes the amount of soil water extracted by industry and households for the purposes of growing organic material. These activities include pasture grazed by cattle and sheep. Figure 1 presented the results for soil water noting that there is a significant decline in soil water supply between 2005-06 and 2009-10. This coincides with a long period of drought and a steep decline in sheep numbers over the same period. Figure 3 shows water applied in irrigation which would typically supplement agricultural production activities. As can be seen in Figures 1 and 3, both soil water abstraction and irrigation decline with prolonged drought conditions.

Figure 3 - Water applied in irrigation
Graph: Figure 3 – Water applied in irrigation

30. Table 2 presents gross soil water abstracted by state. Australia had drought conditions leading up to November 2009 which provides some explanation of the decreased soil water abstraction in 2007-08 and increased soil water abstraction in 2008-09. Queensland has the largest abstraction of soil water in Australia, accounting for between 30% to 35% of soil water entering the economy. The decrease in Queensland from 2005-06 was due to the change in pasture types used for cattle and sheep. There was a substantial increase in modified pasture which in turn has dropped soil water extraction from native pasture, despite the same area being used over the time period. This led to a decrease in soil water extracted of 23% for the state. A similar pattern is seen in New South Wales, where a substantial increase in modified pasture grazing has reduced soil water extraction.

Table 2 - Gross soil water supply, By State

2000-01
2001-02
2002-03
2003-04
2004-05
2005-06
2006-07
2007-08
2008-09
2009-10
2010-11
2011-12
GL
GL
GL
GL
GL
GL
GL
GL
GL
GL
GL
GL

NSW
90 340
100 817
85 111
91 381
91 328
95 266
74 262
59 309
60 521
57 673
73 331
73 996
Vic.
29 762
31 509
28 536
31 861
30 879
31 167
26 031
25 504
23 343
25 094
26 765
26 742
Qld
136 030
152 000
138 659
149 003
151 485
149 643
123 819
94 488
89 801
84 582
99 936
102 316
SA
27 252
38 335
35 778
37 582
35 707
35 368
32 169
30 422
31 675
31 401
39 060
36 352
WA
53 451
67 191
63 739
72 786
71 868
70 253
65 487
61 436
63 115
58 805
50 071
51 827
Tas.
4 618
5 077
5 207
5 216
5 223
5 459
5 224
4 950
4 974
4 671
5 000
5 367
NT
25 706
26 768
25 385
26 105
26 116
27 191
27 983
27 910
22 305
27 846
30 198
30 444
ACT
172
160
122
121
135
135
126
102
107
110
132
153
Aust.
367 330
421 857
382 538
414 054
412 741
414 482
355 099
304 121
295 841
290 183
324 493
327 196




3.2 Soil water use by industry

31. Table 3 shows the allocation of soil water to industry. Sheep, Beef Cattle and Grain Farming has the bulk of soil water use (88% of total soil water use) due to grazing and broadacre crops such as wheat. A substantial part of the decrease in soil water use from 2005-06 onwards was from sheep stocking decreasing steadily due to drought conditions.


Table 3 - Soil water use, by industry

2000-01
2001-02
2002-03
2003-04
2004-05
2005-06
2006-07
2007-08
2008-09
2009-10
2010-11
2011-12
Industry (ANZSIC)
GL
GL
GL
GL
GL
GL
GL
GL
GL
GL
GL
GL

Nursery and Floriculture Production
0
0
0
0
0
0
0
0
0
0
0
0
Mushroom and Vegetable Growing
590
558
480
508
485
668
646
525
544
259
626
516
Fruit and Tree Nut Growing
1 371
1 365
1 435
1 431
1 443
1 577
1 592
1 624
1 071
2 034
1 689
1 504
Sheep, Beef Cattle and Grain Farming
331 875
384 978
351 375
379 238
376 331
374 714
322 896
272 830
261 354
254 851
281 629
290 416
Of which:
Livestock
309 965
361 219
340 768
353 729
355 370
349 629
312 228
257 474
240 744
235 785
256 906
264 033
Other Crop Growing
20 326
21 345
15 319
18 746
19 947
22 489
14 360
13 038
16 367
16 414
23 665
17 757
Dairy Cattle Farming(a)
Poultry Farming
0
0
0
0
0
0
0
0
0
0
0
0
Deer Farming
0
0
0
0
0
0
0
0
0
0
0
0
Other Livestock Farming
0
0
0
0
0
0
0
0
0
0
0
0
Agriculture
354 163
408 246
368 609
399 924
398 206
399 448
339 494
288 017
279 336
273 558
307 609
310 193
Aquaculture
0
0
0
0
0
0
0
0
0
0
0
0
Forestry and Logging
6 198
6 497
6 663
6 713
6 967
7 310
7 694
8 001
8 212
8 175
8 216
8 194
Fishing, Hunting and Trapping
Agriculture, Forestry and Fishing Support Services
Households
6 969
7 114
7 265
7 417
7 568
7 724
7 912
8 103
8 293
8 449
8 668
8 809
Accumulation
Environment
Total use
367 330
421 857
382 537
414 054
412 741
414 482
355 099
304 121
295 841
290 183
324 493
327 196

(a) Included in Sheep, Beef Cattle and Grain Farming.

3.3 Final use of soil water

32. Water incorporated into products and water transpired are components of final water use since they represent flows of water that are no longer available in the economy. Final use estimates are not provided in this article as evaporation should be included but was not measured as a part of soil water abstraction. Water incorporated into products represents the moisture present in organic material as it is harvested from the economy and used over 91,000 ML of water in 2011-12. Harvested material includes pasture grazed by livestock and grass cut in urban environments. Water incorporated in products is quite low compared to soil water supplied, but a significant component of the total biomass recorded under current collection methodology. These data represent a significant component of the plant mass moving through the economy.

Table 4 - Water incorporated in product, State

2000-01
2001-02
2002-03
2003-04
2004-05
2005-06
2006-07
2007-08
2008-09
2009-10
2010-11
2011-12
ML
ML
ML
ML
ML
ML
ML
ML
ML
ML
ML
ML

NSW
25 286
24 582
21 754
23 687
22 927
23 010
20 858
20 149
18 787
19 022
20 578
20 350
Vic.
22 552
21 375
19 929
21 023
21 227
19 883
18 069
18 600
17 250
17 844
17 916
19 029
Qld
32 655
34 989
37 868
38 368
39 541
38 533
35 808
30 646
31 223
29 397
26 516
27 298
SA
9 546
9 372
8 770
9 476
8 777
8 733
7 871
7 672
7 133
7 712
8 573
8 190
WA
11 960
11 447
11 012
12 909
12 635
12 457
11 437
10 492
10 170
9 863
9 053
10 444
Tas.
5 530
5 279
5 564
5 428
5 442
4 889
4 747
4 848
4 389
3 944
3 813
3 409
NT
2 296
2 409
2 268
2 331
2 348
2 433
2 496
2 454
2 006
2 460
2 666
2 690
ACT
107
92
125
85
72
61
50
51
52
51
59
66
Aust.
109 932
109 545
107 290
113 307
112 970
109 998
101 338
94 912
91 011
90 292
89 174
91 476



33. Water transpired (over 327,000 GL of soil water use) is the amount lost to the atmosphere as organic material releases oxygen and water back to the environment through its evapotranspiration processes needed for growth. Under accounts principles this water becomes lost to the economy as it cannot be recovered or re-used despite water entering the atmosphere will eventually be deposited somewhere. Water transpired shows similar changes to soil water supply as only a small amount of water is incorporated in the product harvested.

Table 5 - Water transpired, State

2000-01
2001-02
2002-03
2003-04
2004-05
2005-06
2006-07
2007-08
2008-09
2009-10
2010-11
2011-12
GL
GL
GL
GL
GL
GL
GL
GL
GL
GL
GL
GL

NSW
90 313
100 790
85 088
91 356
91 303
95 244
74 242
59 290
60 503
57 655
73 310
73 976
Vic.
29 741
31 488
28 516
31 840
30 858
31 148
26 013
25 486
23 326
25 077
26 748
26 724
Qld
135 996
151 963
138 621
148 964
151 445
149 604
123 784
94 458
89 770
84 553
99 910
102 289
SA
27 242
38 325
35 769
37 573
35 699
35 360
32 161
30 414
31 668
31 394
39 052
36 344
WA
53 439
67 179
63 728
72 773
71 856
70 241
65 475
61 426
63 105
58 795
50 062
51 816
Tas.
4 615
5 073
5 203
5 212
5 220
5 456
5 220
4 947
4 971
4 668
4 997
5 364
NT
25 704
26 766
25 383
26 102
26 114
27 188
27 980
27 908
22 303
27 843
30 195
30 441
ACT
171
160
122
121
135
135
126
102
107
110
132
153
Aust.
367 222
421 745
382 432
413 942
412 630
414 376
355 001
304 030
295 753
290 095
324 406
327 106


3.4 Conclusions and further improvements

34. Soil water supply and use can be regularly measured in the Water Account Australia (WAA) (ABS cat. no. 4610.0). Due to the scope of the changes proposed in this article, incorporation into the existing WAA will be challenging. It is recommended that Australia adopts the international standard for presentation of water accounts from either SEEA 2012 or SEEA-Water. This would allow clearer separation of supply of natural inputs from residual flows back to the environment and improve comprehension of the economic concepts of inputs into the economy (gross water input) and losses which cannot be recovered by the economy (final use of water). Further work on calculating evaporation of abstracted water would also be useful. Comments on the methods and sources of data used in this article can be submitted at <environment@abs.gov.au>.


BIBLIOGRAPHY

35. Bibliography available on request from <environment@abs.gov.au>.

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