Agricult Water Demand Maipo

2011

ANALYSIS OF AGRICULTURAL WATER

DEMANDS IN THE MAIPO BASIN TECHNICAL REPORT

2

TABLE OF CONTENTS

Introduction ........................................................................................................................................................ 3

Total agricultural area in the metropolitan region ............................................................................................. 4

Agricultural structure ......................................................................................................................................... 5

Irrigated area and Relation between kind of irrigation and size of agricultural holdings ................................ 11

Area covered by natural vegetation ................................................................................................................. 16

Share of different crops in the total agricultural area ...................................................................................... 16

Share of different crops in the irrigated agricultural area................................................................................ 17

General TRends since 1960 .............................................................................................................................. 18

Prognosis for future scenarios .......................................................................................................................... 21

Vegetation periods for rm main crops ............................................................................................................. 29

Evapotranspiration of the mian crops in rm..................................................................................................... 32

Economic benefits in terms of water consumption ......................................................................................... 37

Virtual water exchange .................................................................................................................................... 39

Water Use rights ............................................................................................................................................... 39

References ........................................................................................................................................................ 43

3

INTRODUCTION

In this document, the “Centro de Cambio Global (CCG-UC)” of the Pontificia

Universidad Católica de Chile, is a technical report whose aim is to synthesize information

regarding the “Agricultural water demands of the Maipo basin”. The main objectives of

this work were document and characterize the impact of agriculture on water demands in

the Maipo basin, and establish some indices that allow researchers to make

recommendation about suitable adaptation strategies that improve water use efficiency

under climate change scenarios.

Chile is divided into 15 administrative regions. One of them is the Metropolitan Region

(RM) who hosts the capital of the Chilean Republic, Santiago of Chile. The RM

concentrates 40.1% of the national population with almost 6 millions of inhabitants and

covers nearly 15.500 km2, representing the 2% of the national territory. According to the

Central Bank (Banco Central, 2006) almost 42.5% of the total Gross Domestic Product of

the country is generated within the RM, being the most important sectors financial

services, manufacturing industry, commerce and touristic services. This region is

characterized by a Mediterranean climate with a long dry season. Mean annual

temperature is around 14 ºC, with the warmest values observed in January (22.1 ºC) and

the coldest in July (7.7 ºC). Total annual precipitation reaches 356.0 mm on average. The

presence of the Andes in the east of the region allows the storage of snow during the

winter which is responsible of the nival regime of the main rivers in the region (Maipo and

Mapocho) and ensures water supply for the population and for irrigation during the dry

season.

Only close to 1.2 % of the regional GDP of the RM corresponds directly to agriculture,

but the exportation goods, like quality fruits, contributes to the financial and merchandise

GDP of the region.

4

TOTAL AGRICULTURAL AREA IN THE METROPOLITAN REGION

According to the latest agricultural census (INE, 2007), the RM accounts for a total of

1136259.97 Ha classified as agricultural lands. Nevertheless, 982867.93 Ha correspond to

shrub land, natural forests, improved and natural pastures and non profitable lands.

Figure 1 presents the distribution amongst these different categories.

13%

14%

14%

20%

36%

3%

Total Agricultural Area in RM

Crops (153392.04 Ha)

Pastures (158468 Ha)

Natural Forest (142222 Ha)

Shrub Land (224796 Ha)

Non Profitable Lands (412653 Ha)

Others (29095 Ha)

Figure 1: Distribution of Total Agricultural Area in the RM (INE, 2007).

The 153392.04 destined to crops are divided in three principal categories, annual crop

and fruit orchards, permanent and rotation fodders and fallow lands. The distribution

amongst the different categories is shown in Figure 2.

5

74%

11%

15%

Distribution of Total Agricultural Area in RM

Annual Crops and Fruit Orchards (113270.29 Ha)

Permanent and Rotation Fodders (16678.20 Ha)

Fallow Lands (23443.55 Ha)

Figure 2: Distribution of Crop surface in the RM.

AGRICULTURAL STRUCTURE

Figure 3 shows the distribution of the Total Agricultural area in the RM with respect to

different holding sizes.

6

0% 1% 1%2%

4%3%

5%

7%

5%

6%66%

Size of the Different Holdings in RM

Less than 1 Ha (813.99 Ha)

From 1 to 5 Ha (8400.61 Ha)

From 5 to 10 Ha (14414.23 Ha)

From 10 to 20 Ha (22181.62 Ha)

From 20 to 50 Ha (43281.67 Ha)

From 50 to 100 Ha (41674.57 Ha)

From 100 to 200 Ha (53419.21 Ha)

From 200 to 500 Ha (76419.89 Ha)

From 500 to 1000 Ha (57974.64 Ha)

From 1000 to 2000 Ha (69179.40 Ha)

More than 2000 Ha (748499.14 Ha)

Figure 3: Size of the Different Holdings in RM.

In Figure 3 we can appreciate the distribution of holdings by size including total

agricultural lands, plus natural end improved pastures, shrub lands and natural forests. It

is possible that holdings of 1000 Ha and more include also natural pastures and high

mountain lands without any agricultural use since they are non profitable lands. On the

other hand, Figure 4 shows how this 1136259.67 Ha are distributed by holdings size.

7

Figure 4: Number of Holdings by size (INE, 2007).

In Figure 4 is shown that the largest amounts of holdings are grouped between 1 and 50 Ha.

Yet, as shown in Figure 3 it is possible to conclude that a big part of the agricultural area of RM,

including pastures and shrub land and non profitable lands, are owned by few farmers.

Each kind of holding, arranged by size, has a different agricultural structure. In table 1, it is

possible to observe the different kind of crops grouped by holding size. The relative area occupied

by each crop (%) is organized as a function of the total cultivated area for each category.

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

Less than 1 Ha

(1512)

From 1 to 5 Ha

(3581)

From 5 to 10 Ha

(2027)

From 10 to 20 Ha

(1594)

From 20 to 50 Ha

(1390)

From 50 to 100 Ha (606)

From 100 to 200 Ha

(385)

From 200 to 500 Ha

(253)

From 500 to 1000 Ha

(85)

From 1000 to 2000 Ha

(52)

More than 2000 Ha

(70)

Nu

mb

er

of

Ho

ldin

gs

Holdings grouped by size

Number of Holdings by size in RM

8

Table 1: Distribution of main crops by holding size

Less than 10 Ha 10-20 Ha

Crop Area (Ha) (%) Crop Area (Ha) (%)

Alfalfa 1920.7 13.30 Alfalfa 1442.2 11.45

Potato 1071.9 7.42 Potato 744.1 5.91

Corn 876.4 6.07 Corn 707.2 5.61

Sweet Corn 781.4 5.41 Lettuce 642.7 5.10

Avocado 753.7 5.22 Sweet Corn 570.7 4.53

Lettuce 639.3 4.43 Walnut 460.4 3.65

Walnut 380.5 2.64 Table Grapes 418 3.32

Tomato 325.1 2.25 Avocado 391.1 3.10

Lemon 318.9 2.21 Pumpkin 292.8 2.32

Bean 301.4 2.09 Fescue 278.1 2.21

Total 7369.3 51.0 Total 5947.3 47.2

Total Cultivated Area

14441.665 100.00 Total Cultivated

Area 12599.5 100.00

20-50 Ha 50-100 Ha


Alfalfa 2173.7 9.07 Alfalfa 2186.4 9.77

Table Grapes 1294.2 5.40 Corn 1599.7 7.15

Corn 1202.4 5.02 Table Grapes 1581.1 7.06

Vineyards 1193.2 4.98 Vineyards 1426.7 6.38

Potato 1064.3 4.44 Walnut 1188.8 5.31

Lettuce 1040.5 4.34 Potato 1170.6 5.23

Walnut 933.6 3.89 Seed Corn 579.2 2.59

Eruropean Plum 784.4 3.27 Pumkin 561.2 2.51

Avocado 647.8 2.70 European Plum 450.7 2.01

Sweet Corn 611.6 2.55 Walnut 448.7 2.00

Total 10945.7 45.7 Total 11193.1 50.0



Area 22382.58 100.00

9

Table 2: Distribution of main crops by holding size (Continued)

100-200 Ha 200-500 Ha


Table Grapes 2516.4 13.03 Vineyard 3611.7 14.62

Alfalfa 2074.2 10.74 Table Grapes 2211.1 8.95

Corn 1376.9 7.13 Corn 2066 8.37

Vineyard 1214.41 6.29 Avocado 2016.4 8.16

Pumkin 618.9 3.20 Alfalfa 1951.6 7.90

Walnut 526.3 2.73 Others Fruit Crops 1804.6 7.31

Fescue 515 2.67 Corn 593 2.40

Avocado 486.4 2.52 Peach 576.5 2.33

Seed Corn 478.1 2.48 Avocado 533.9 2.16

Almond 372.5 1.93 Potato 476.7 1.93

Total 10179.1 52.7 Total 15841.5 64.1



Area 24695.7 100.00

500-1000 Ha 1000-2000 Ha


Avocado 1534.7 16.13 Vineyard 968.9 16.24

Corn 1188.9 12.50 Table Grapes 950.2 15.93

Vineyard 1119.6 11.77 Avocado 363.7 6.10

Alfalfa 765.6 8.05 Almond 327.8 5.50

Table Grapes 705.5 7.42 Japanese Plum 312.2 5.23

Lemon 410.6 4.32 Corn 290.3 4.87

Orange 343.3 3.61 Alfalfa 287.1 4.81

Corn 238.0 2.50 European Plum 177 2.97

Almond 238.0 2.50 Falaris 152 2.55

Olive 155.5 1.63 Corn 151.5 2.54

Total 6699.7 70.4 Total 3980.7 66.7



Area 5965.2 100.00

10

Table 3: Distribution of main crops by holding size (Continued)

More than 2000 Ha

Crop Area (Ha) (%)

Corn 2579.0 26.91

Vineyard 2028.4 21.16

Alfalfa 695.0 7.25

Table Grapes 422.3 4.41

Avocado 322.1 3.36

Oat 280.0 2.92

Forage Mix 201.0 2.10

Potato 197.0 2.06

European Plum 164.3 1.71

Wheat 163.0 1.70

Total 7052.1 73.6


9584.11 100.00

Table 1 shows many important aspects of the RM agricultural organization. In the first place,

we can observe that no crop by it by its one explains most of the cultivated area arranged by

holding size. An important aspect is that in smaller holdings the mayor crop corresponds to

Alfalfa with cattle feeding purposes. Also, fruit orchards don’t represent a large area in this kind

of holdings. Nevertheless, in largest holdings we start to see the strong presence of Table Grapes,

Vineyards and Avocado plantations since the largest holdings are related to more significant

investments and the possibility of exportation.

11

IRRIGATED AREA AND RELATION BETWEEN KIND OF IRRIGATION AND SIZE OF

AGRICULTURAL HOLDINGS

According to the 2007 agricultural census they are a total of 136144.2 Ha irrigated by

different systems. Figure 5 shows the distribution of the different kind of irrigation in the

RM total irrigated area.

Figure 5: Total RM irrigated area by kind of irrigation.

The total irrigated area from RM is dominated principally by furrow and flood irrigation,

particularly for corn and alfalfa, meanwhile, drip and micro sprinkler irrigation are

supposed to be more present in the fruit orchards of the region.

The next sequence of figures shows the distribution of kind of irrigation by holding size.

41%

24%

27%

4%

2% 1% 1%

Distribution of RM total irrigated Area by kind of irrigation

Furrow Irrigation (56228.18 Ha)

Flood Irrigation (32691.82 Ha)

Drip Irrigation (37442.52 Ha)

Micro Sprinklers Irrigation(4783.77 Ha)

Irrigation by Drag Hoses (3022.7Ha)

Other (1093.72 Ha)

Sprinklers Irrigation (881.53 Ha)

12

Figure 6: Distribution of irrigated area in Holdings with less than 10 Ha.

Figure 7: Distribution of irrigated area in 10 to 20 Ha Holdings.

61%

29%

7%

2% 0% 1%

0%

Distribution of irrigated area in Holdings with less than 10 Ha

Furrow Irrigation (8324.19Ha)




Irrigation by Drag Hoses (3.7 Ha)

Other (118.27 Ha)


56% 32%

9%

2% 0% 1% 0%

Distribution of irrigated area in 10-20 Ha Holdings





Irrigation by Drag Hoses (4.5 Ha)

Other (95.9 Ha)

13



51%

25%

19%

4%

0% 1% 0%






Irrigation by Drag Hoses (16 Ha)

Other (144.35 Ha)


47%

25%

24%

3%

0% 1% 0%





Micro Sprinklers Irrigation (651.6Ha)


Other (155.9 Ha)


14



35%

25%

33%

3% 1% 2% 1%



Flood Irrigation (4589 Ha)



Irrigation by Drag Hoses (255.5Ha)

Other (410.3 Ha)


32%

22%

37%

4% 4%

0% 1%







Other (68 Ha)


15



19%

13%

47%

8%

9%

1%

3%







Other (37.5 Ha)


12%

21%

63%

2% 2% 0% 0%




Drip Irrigation (3803 Ha)

Micro Sprinklers Irrigation (131Ha)


Other (0.5 Ha)

Sprinklers Irrigation (25 Ha)

16

Figure 14: Distribution of irrigated area in Holdings with more than 2000 Ha.

AREA COVERED BY NATURAL VEGETATION

According to the latest agricultural census (INE, 2007), the RM accounts for a total of

1136259.97 Ha classified as agricultural lands. Shown in figure 1, 982867.93 Ha

correspond to shrub land, natural forests, improved and natural pastures and non

profitable lands. The sum of shrub lands and native forests accounts for 367018 Ha.

SHARE OF DIFFERENT CROPS IN THE TOTAL AGRICULTURAL AREA

Table 2 shows the distribution of different crops in the RM. The percentage is given in

function of the total cultivated area of 142469.5 Ha.

33%

21%

34%

2% 8%

1% 1%

Distribution of irrigated area in Holdings with more tha 2000 Ha






Other (63 Ha)

17

Table 2: Distribution of main crops in Metropolitan Region

Crop Area (Ha) (%)

1 Corn 13948.4 9.68

2 Alfalfa 13496.5 9.36

3 Table Grapes 10247.7 7.11

4 Vineyard 10161.02 7.05

5 Avocado 5841.5 4.05

6 Potato 5171.3 3.59

7 Walnut 4058 2.82

8 Sweet Corn 3260.1 2.26

9 Lettuce 3040.542 2.11

10 Lemon 2689.8 1.87

11 European Plum 2588.9 1.80

12 Almond 2574.8 1.79

13 Pumpkin 2391.3 1.66

14 Japanese Plum 2050.1 1.42

15 Orange 1978.2 1.37

TOTAL 83498.162 57.94

SHARE OF DIFFERENT CROPS IN THE IRRIGATED AGRICULTURAL AREA

Because of strong seasonality in precipitation, all crops showed in table 2 are regarded

as irrigated crops in the RM. Although some minor annual crops are grown in rain fed

conditions (Only 579 Ha of wheat and 640.3 Ha of oat for forage, representing only the

18

0.8% of the total agricultural area), it is virtually impossible to get commercial yields under

these conditions.

GENERAL TRENDS SINCE 1960

Evaluating the IV (1965), V (1978), VI (1997) and VI (2007) agricultural census it is

possible to observe the general evolution since 1960 to nowadays regarding total

agricultural area, agricultural structure, total irrigated area and natural vegetation for the

RM.

a) Total RM Agricultural Area.

Figure 15: General trend for Total Agricultural Area.

We can observe a trend concerning a constant reduction of the total agricultural

area. However, since 1997 to 2007 it is possible to see a little augmentation. This could be

referred to a change in census classification for the “Agricultural Area” item. It seems that

0

200000

400000

600000

800000

1000000

1200000

1400000

1600000

1800000

1965 1978 1997 2007

He

ctar

es

Year

Total Agricultural Area (Ha)

19

during the last decade (1997-2007) there is a change in the general trend pointing to a

stabilization in the total agricultural area in RM.

b) Agricultural Structure.

Figure 16: General trend for agricultural area arranged by holding size.

For the agricultural area arranged by holding size we can expect a very little reduction

in the smallest holdings (less than 10 Ha) and a strong decrease in the biggest holdings

(more than 1000 Ha). Again, a little augmentation from 1997 to 2007 could be explained

by changes in the census agricultural area classification and a slight tendency towards the

consolidation of medium size agriculture to achieve a reasonable scale of production.

0

200000

400000

600000

800000

1000000

1200000

LessThan 10

Ha

From 10to 20 Ha

From 20to 50 Ha

From 50to 100

Ha

From100 to200 Ha

From200 to500 Ha

From500 to

1000 Ha

From1000 to2000 Ha

Morethan

2000 Ha

He

ctar

es

Different kind of Holding

Agricultural Area by Holding size

1965

1978

1997

2007

20

Figure 17: General trend for number of holding arranged by size.

The most important change concerning number of holdings arranged by their size is in

holdings with less than 10 Ha. For holdings within 10 and 50 Ha we can appreciate a little

augmentation in the number of holdings, but in bigger holdings the number of holdings

seems not to change a lot.

Due to the information available in the last census is not possible to separate the

different kind of irrigation by holding size. Only trend in the general irrigated area is

shown.

0

5000

10000

15000

20000

25000N

um

be

r o

f H

old

ings

Different kind of Holding

Trend in number of Holdings

1965

1978

1997

2007

21

Figure 18: General Trend for Irrigated area arranged by holding size.

It is possible to see a general reduction in the irrigated area, as it was observed in

agricultural area.

PROGNOSIS FOR FUTURE SCENARIOS

Land use change is a complex, multifactorial process, which can only be represented

with models that allow for non linear factors and learn from past experiences (examples

are artificial neural networks). These models are not available for the agricultural sector.

We can however provide some projections based on observed trends. Taken the

information of the latest four agricultural censuses we could get a general trend for the

agricultural area, agricultural structure, irrigation area and natural vegetation. From these

0

20000

40000

60000

80000

100000

120000

140000

160000

180000

200000

Irrigated area by Holding size

1965

1978

1997

2007

22

data new could model the future scenarios for year 2030, 2060 and 2100. The best fit was

with an exponential model given by:

Where Y represents the surface value of the variable of interest, X is the year since

1960, and “a” and “b” represent the parameters of the equations.

The different factors (ln(a) and b) and the respective R2 are given in table 3 for all the

regression used for the construction of the future scenarios. Each regression was made

from the respective data of the IV, V, VI and VII agricultural census, only four observations.

When the fit of the model was not good, we try with a linear fit improving the

approximation.

Table 3: Coefficient used for the Modeling of different Future Scenarios

Agricultural Area by Holding Size

Ln(a) b R^2

Less Than 10 Ha 10.81 -0.16 0.55

From 10 to 20 Ha 9.30 0.19 0.85

From 20 to 50 Ha 10.01 0.16 0.82

From 50 to 100 Ha 10.07 0.12 0.70

From 100 to 200 Ha 10.54 0.07 0.31

From 200 to 500 Ha 11.30 -0.04 0.17

From 500 to 1000 Ha 11.37 -0.12 0.86

23

From 1000 to 2000 Ha 12.50 -0.35 0.97

More than 2000 Ha 14.22 -0.19 0.96

Total 14.51 -0.16 0.96

Less Than 10 Ha 10.81 -0.16 0.55

Number of Holdings arranged by their Size

Ln(a) b R^2

Less Than 10 Ha 10.71 -0.42 0.80

From 10 to 20 Ha 6.69 0.19 0.86

From 20 to 50 Ha 6.56 0.16 0.83

From 50 to 100 Ha 5.81 0.13 0.74

From 100 to 200 Ha 5.56 0.08 0.36

From 200 to 500 Ha 5.52 -0.02 0.05

From 500 to 1000 Ha 4.79 -0.10 0.82

From 1000 to 2000 Ha 5.18 -0.32 0.97

More than 2000 Ha 5.36 -0.29 1.00

Total 10.61 -0.29 0.83

24

Table 3: Coefficient used for the Modeling of different Future Scenarios (Continued)

Irrigated Area by Holding Size

Ln(a) b R^2

Less Than 10 Ha 10.55 -0.21 0.36

From 10 to 20 Ha 8.56 0.27 0.75

From 20 to 50 Ha 8.97 0.31 0.82

From 50 to 100 Ha 9.25 0.20 0.77

From 100 to 200 Ha 10.19 -0.08 0.80

From 200 to 500 Ha 10.71 -0.20 0.67

From 500 to 1000 Ha 10.62 -0.47 0.81

From 1000 to 2000 Ha 10.75 -0.60 0.84

More than 2000 Ha 10.62 -0.40 0.90

Total 12.30 -0.12 0.98

Natural Vegetation Area

Ln(a) b R^2

Natural Vegetation Area -290.746392 39.9087507 0.73

25

Figure 19 shows the prognosis for total agricultural area.

Figure 19: Estimated surface of total agricultural area by year.

The future decrease in agricultural area could be explained by changes in land use

change and the expansion of Santiago city.

The prognosis for agricultural structure arranged by agricultural area by holdings size is

shown above.

0

200000

400000

600000

800000

1000000

1200000

2007 2030 2060 2100

Surf

ace

(H

a)

Year

26

Figure 20: Estimated surface by holding size.

We can observe an important decrease in the agricultural area in holdings with more

than 1000 Ha. Nevertheless there is an increase in the agricultural area in holdings ranged

between 10 and 200 Ha.

Figure 21 shows the number of farms arranged by holding size.

0

200000

400000

600000

800000

1000000

1200000Su

rfac

e (

Ha)

Holding Size

Prognosis for Agricultural Area by Holding Size

2007

2030

2060

2100

27

Figure 21: Estimated number of farms by Holding Size

There is a clear reduction in the number of holdings with less than 10 Ha, on the

contrary the number of holdings ranged between 10 and 100 Ha seems to increase.

According to the model, a change in the number of holdings between 200 and 2000 Ha is

not expected.

Total irrigated area follows a similar trend that the agricultural area. Next figure shows

the estimated value for total irrigated area in RM.

0

2000

4000

6000

8000

10000

12000

14000

Number of Holdings by their Size

2007

2030

2060

2100

28

Figure 22: Estimated value of irrigated area and Irrigated area by holding size.

0

20000

40000

60000

80000

100000

120000

140000

160000

Prognosis of RM Irrigated Area

2007

2030

2060

2100

29

Figures 23 shows the evolution of natural vegetation expected in the future.

Again, a change in natural vegetation classification in the census could undermine the

future changes in the forest and shrub land areas.

VEGETATION PERIODS FOR RM MAIN CROPS

According to table 2 the main crops in RM are: alfalfa, corn, table grapes, vineyards and

avocados. The central valleys of Chile are well known by their good condition for the

production of quality fruits for exportation to USA, Europe and Asia. In the case of alfalfa

and corn, it is expected that this two goods in RM are produce for animal feeding.

In table 3 it is possible to appreciate the difference between the phenology of RM main

crops. Periods of vegetation growth will be associated with an increase on water demand

by the crop.

0

500000

1000000

1500000

2000000

2500000

2007 2030 2060 2100

He

ctar

es

Year

Prognosis for Natural Vegetation Area

30

a) Alfalfa

For the specific case of alfalfa in RM it is important to note that typically the farmers

are use to make for cuts of the plant during the season thanks to capacity to growth again

during the warmest part of the year.

Table 4: Vegetation Periods for Alfalfa

Crop Sept Oct Nov Dec Jan Feb Mar Apr May Jun Jul Ago

Alfalfa Shoot Growth

First Cut

Shoot Growth

Second Cut

Shoot Growth

Third Cut

Shoot Growth

Fourth Cut

Dormancy

After each cut the alfalfa starts to grow up again, changing its leaf area index and

increasing its water demand.

b) Corn:

They are different kinds of corn with differences in planting and haversting dates.

However in RM the most used corn is it an intermediate variety which is planted at

September and harvested during March, when the grain reaches 14% oh humidity. Table 4

shows the most important events regarding the vegetation periods for corn.

Table 5: Vegetation Periods for Corn


Corn Planting Leaf

development Flowering

Senescense

Grain Harvest

c) Table Grapes and Vineyards:

The most important crops in RM are the one related with grapes either for fresh

consumption or for the elaboration of quality wines. Nevertheless the phenology for both

is very similar, changing only for harvesting date depending on the variety of table grapes

or in the case of the wine if they are white or red grapes. Red grapes trends to be

harvested in March-April meanwhile white grapes are harvested during February and

31

March. In RM the most important kind of grapes corresponds to the ones for red wine

elaboration. Table 4 shows the corresponding phenology for grapes.

Table 6: Vegetation Periods for Table Grapes and Vineyards


Vineyards Bud Breack Shoot

Growth Cane Maturation Leaf Fall Dormancy Flowering Fruit Harvest

d) Avocado:

The avocado tree corresponds to an evergreen, so at any time of the year their leaves

fall, causing a permanent evapotranspiration during all the season. Spite of its evergreen

nature avocado has two flushes of vegetative growth and a little leaf fall next to autumn.

In table 6 it is possible to appreciate the vegetation periods of the avocado.

Table 7: Vegetation Periods for Avocadoes


Avocado

First Shoot Growth

Second Shoot Growth Small Leaf Fall

Flowering/ Harvest Harvest Harvest Harvest %%%%%%%%%%%% Fruit Maturation %%%%%%%%

32

EVAPOTRANSPIRATION OF THE MIAN CROPS IN RM

For the determination of the evapotranspiration of RM main crops a reference

evapotranspiration (ET0) was taken for the region made from Penmann-Monteith’s

equation. The evolution of ET0 for the RM is show in figure 24.

Figure 24: Evolution of the Seasonal ET0 in RM

As expected the ET0 for the summer months were higher than the ones during the

winter.

Adjusting the different crops coefficient given by FAO (Allen et al., 1998) for each crop

and vegetation period it is possible to get the seasonal and total water demand for alfalfa,

corn, table grapes, vineyards and avocadoes.

0

1

2

3

4

5

6

7

8

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

ET0 (

mm

day

-1)

Month

Seasonal ET0 in RM

33

Taking the ET0 average by day for each month and multiplying it by the numbers of day

of each month it is possible to obtain the water demand by hectare express as m3 Ha-1

month-1. The sum of all months will give the total demand for each crop by year in terms

of cubic meters of water by hectare. This is indeed a proxy for irrigation water demands

since most of precipitation falls in winter and the use of irrigation is mandatory between

October and March in order to obtain economically feasible yields.

In figure 25 it is possible to see the variation of the water demand for alfalfa during the

all season.

Figure 25: Water demand for Alfalfa during the year.

The different picks correspond to changes in the crop coefficient driving mainly by the

cuts of the alfalfa. The yearly water demand of the alfalfa corresponds to an average of

13083 m3 of water by Ha.

For the case of the corn we start with an initial Kc at the planting date. In comparison to

alfalfa there is not winter water demand for corn, only from September to late February it

0

500

1000

1500

2000

2500

3000


m3 H

a -1

mo

nth

-1

Month

Water Demand (m3 Ha -1) by Month for Alfalfa

34

is necessary the irrigation of the crop. Figure 26 shows the variation of the corn’s water

demand through the year.

Figure 26: Water demand for Corn during the year.

During the season an Hectare of corn in the RM consumes an average of 10000 m3 of

water.

The seasonal change in water consumption for table grapes is shown in figure 27.

During winter the water demand by vines drop to zero, however, ones the bud break

arrives the water consumption begin to increase.

0

500

1000

1500

2000

2500

3000


m3 H

a -1

mo

nth

-1

Month

Water Demand (m3 Ha -1) by Month for Corn

35

Figure 27: Water demand for Table Grapes during the year.

The total water demand for table grapes corresponds to an average of 8024 m3 of

water by Ha by year.

Water demand for vineyards was also obtained with FAO’s Kc. Nevertheless the

quantity of water irrigated could vary greatly depending on the type and quality of wine

that is expected by each holding. Figure 28 shows the seasonal variation in water

vineyard’s water demand.

0

200

400

600

800

1000

1200

1400

1600

1800


m3 H

a -1

mo

nth

-1

Month

Water Demand (m3 Ha -1) by Month for Table Grapes

36

Figure 28: Water demand for Vineyards during the year.

The total water demand of vineyards corresponds to 7045 m3 of water by Ha by year.

Avocado, as an evergreen specie has a water demand during all the year. After the little

leaf fall during autumn it Kc drops until spring were a new flash of growth increases the

water demand with respect to ET0.

Figure 29 shows the variation of the water demand by avocadoes trees during the year.

0

200

400

600

800

1000

1200

1400

1600


m3 H

a -1

mo

nth

-1

Month

Water Demand (m3 Ha -1) by Month for Vineyards

37

Figure 29: Water demand for Avocadoes during the year.

The total water demand for an hectare of avocado corresponds to 11152 m3 of water

by year.

ECONOMIC BENEFITS IN TERMS OF WATER CONSUMPTION

For the determination of the economic benefits derived from the use of water by each

crop it was necessary to estimate an average irrigation efficiency ones the total water

demand of plants, in terms of water cubic meters by hectare was determined. For each

kind of irrigation a given efficiency was taken from FAO. Then it was possible to calculate

an average of irrigation efficiency for the different holdings that cultivate one of our crops

of interest: alfalfa, corn, table grapes, vineyards and avocadoes.

Information about commercial prices for alfalfa, corn and wine grapes and FOB (Free

On Board) values by tons for table grapes and avocadoes were taken from the National

Bureau of Agricultural Policies (ODEPA, 2011). It is important to remember that the fruit

0

200

400

600

800

1000

1200

1400

1600

1800

2000


m3 H

a -1

mo

nth

-1

Month

Water Demand (m3 Ha -1) by Month for Avocado

38

production in RM centers in an exportation market. However alfalfa and corn are

cultivated for animal feeding. For the specific case of wine grapes it is very difficult to

determine a specific price, since it will vary greatly depending on its quality. We have

expressed net benefits for table grapes for internal market as well as for export. Table 4

shows the different factors used in the estimation of economic performance in terms of

water consumed by each crop. Note that cost expressed here are operational cost only.

The irrigation efficiency varies within each irrigation method. Drip irrigation presents a

high efficiency rate, close to 90%. That means that closely 90% of the water given by drip

irrigation rest available for the plant. Next table shows the different irrigation efficiencies

for each irrigation technology. This table was obtain from Allen et al. 1998.

Table 8: Irrigation efficiencies for each Irrigation System

Irrigation System Field application

efficiency

Surface irrigation (border, furrow, basin) 60%

Sprinkler irrigation 75%

Drip irrigation 90%

In RM typically, fruit orchards, as Table Grapes and Avocadoes, and vineyards counts

with drip irrigation systems with an efficiency close to 90%. Nevertheless minor orchards

present sprinkler irrigation and surface irrigation. For the assessment of the irrigation

efficiency for each crop raw data from national agricultural census was obtained from

Windows Access. It is impossible to determine the specific irrigation efficiency for each

crop, but it is possible to determine a weighted average irrigation efficiency for each

holding that has one of the five main crops. However, alfalfa is normally irrigated by flood

irrigation, corn by furrow and Table Grapes, avocadoes and vineyards are irrigated by drip

irrigation.

The weighted average irrigation efficiencies expressed in Table 9 do not differ very

much from the traditional irrigation technologies used for each crop (Flood, Furrow and

Drip Irrigation, expressed before).

39

Table 9: Water Demand and Economical Profit for each Crop

Irrigation efficiency

Irrigation (m3 Ha-1)

Yield (Ton Ha-1)

Crop Value (US$ Ton-1)

Mean Cost (US$/Ha)

Net Benefit (US$ Ha-1)

Water Profit (US$

m-3)

Water demand

(m3 y-1 Ha-1)

Alfalfa 13088 0.6 21813.33 17 143.14 1200 1233.38 0.056

Corn 10099 0.62 16288.71 13 270.59 1900 1617.67 0.099 Table Grapes 8023 0.88 9117.05 32 2500 60000 20000 2.193

Vineyards1 7045 0.86 8191.86 15 352.94 3800 1494.1 0.182

Avocado 11153 0.89 12531.46 10 1423.1 3500 10731 0.856

VIRTUAL WATER EXCHANGE

As mentioned before the fruit production in RM is meanly thought as exportation good.

No data is available to determine the water virtual exchange from RM. However it is

supposed that most part of table grapes and avocadoes are produce for exportation. For

wine grapes, depending on its quality, the pattern is the same.

For the case of alfalfa and corn, both with animal feeding purposes, it is supposed that

all the production stays in the RM. Again information is not available.

1. We have not considered here the possibility of wine making. We have assumed that

farmers produce grapes that are sold to wine making companies

40

WATER USE RIGHTS

Detailed information about water use rights in the Maipo basin is difficult to obtain. Some

general reports allow us to determine that there are, for instance, approximately 8100

shares distributed in the first section of Maipo.

As a general statement we can say that almost 75% of water use rights are allocated to

irrigated agriculture in the Maipo area.

A study of DGA (2003), whose objective was to determine the availability of water rights,

concluded that there are no more permanent rights to be allocated in the basin.

If we assume as the 15% percentile as the level for the distinction between permanent

and contingent water use rights we can estimate the flow allocated for different purposes

as showed in Table 10.

41

Table 10: Allocated Flow m3 s-1

Section Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar

Maipo

Las Hualtatas 18.15 14.41 12.92 12.65 12.22 12.8 18.56 36.08 36.29 36.26 32.84 25.59

Maipo

Las Melozas 24.78 19.56 18.44 17.83 16.93 18.85 29.29 60.11 78.5 64.56 47.81 35.82

Maipo

San Alfonso 3.68 6.97 6.11 7.86 8.69 9.58 12.6 15.9 11.1 8.2 10.2 4.38

Maipo

Manzano 178.4 178.4 178.4 178.4 178.4 178.4 178.4 178.4 178.4 178.4 178.4 178.4

Rio Volcan 2.93 2.93 2.93 2.93 2.93 2.93 2.93 2.93 2.93 2.93 2.93 2.93

Rio Yeso 3.24 2.75 2.55 2.36 2.37 2.41 3.11 4.86 5.32 5.22 4.58 3.92

Rio

Colorado 3.26 2.27 2.06 1.98 2.04 2.07 3.02 4.81 7.81 9.91 10.34 6.58

Maipo

Angostura 14.59 14.59 14.59 14.59 14.59 14.59 14.59 14.59 14.59 14.59 14.59 14.59

Maipo

Naltahua 5.77 5.87 5.96 6.03 6.02 5.91 5.56 6.9 5.93 5.76 5.76 6.03

Mapocho Almendros 6.33 5.87 5.87 5.87 5.87 6.36 6.82 7.35 7.96 7.52 7.42 6.75

Mapocho

Rinconada 42.98 42.98 42.98 42.98 42.98 42.98 42.98 42.98 42.98 42.98 42.98 42.98

Maipo

Puangue 50.5 97.9 103. 119.6 111.2 55.4 46.4 50.5 51.3 52.4 50.1 51.1

Maipo

Cabimbao 15 24 24 24 24 19 22 20 18 18 46 39

42

Total agricultural demands in the Maipo area can be estimated as

Month Demand (m3/s)

April 83.9

May 70.4

June 65.9

July 66.1

August 64.9

September 82.7

October 113.6

November 135.95

December 150.2

January 148.0

February 141.4

March 99.05

Average 101

43

REFERENCES

ALLEN R.G., PEREIRA L.S., RAES D., SMITH M., 1998. Crop evapotranspiration-guidelines for computing crop water requirements. Irrigation and Drainage No. 56, FAO, Rome 300 pp.

Banco Central, 2006. Estadísticas Económicas. Santiago de Chile. www.bcentral.cl

(Consulted: March 3th, 2011). INE, IV Censo Nacional Agrícola, 1965. Santiago of Chile. INE, V Censo Nacional Agrícola, 1978. Santiago of Chile. INE, VI Censo Agropecuario Nacional, 1997. Santiago de Chile. INE, VI Censo Agropecuario Nacional, 2007. Santiago de Chile ODEPA, Estadísticas por rubros, 2011. Santiiago de Chile. www.odepa.gob.cl (Consulted: April 5th, 2011)

http://www.bcentral.cl/

http://www.odepa.gob.cl/

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