Groundwater level decline

The observation of a trend of continuous significant decline in groundwater levels is frequently considered an indicator of imbalance between abstraction and recharge. While this may be most frequently the case, the approach may be somewhat simplistic and misguided. Custodio (2000) and Sophocleous (2000) remind us that any groundwater withdrawal causes an increasing piezometric depletion until a new equilibrium is achieved between the pumpage and the

Table 13.3. Descriptive elements of Irrigation in Spain (in hectares). (From MAPYA, 2001.)

Predominant irrigation technique (%)

Table 13.3. Descriptive elements of Irrigation in Spain (in hectares). (From MAPYA, 2001.)

Autonomous Community

Surface water

Groundwater

Inter-basin transfers

Water returns

Reuse

Desalinized

Total

Flood

Sprinkler

Drip irrigation

Andalusia

546,703

224,670

2,783

85

5,639

779,880

42

21

37

Aragón

373,886

20,315

21

394,222

80

18

2

Castilla-León

361,055

113,164

12,428

29

486,676

61

39

-

Castilla-La

Mancha

124,262

228,528

1,011

353,801

32

55

13

Cataluña

205,031

53,043

6,377

342

264,793

69

12

19

Extremadura

207,337

3,151

210,488

69

26

5

Galicia

85,061

92

85,153

64

36

-

Murcia

42,553

93,810

51,104

360

1,600

271

189,698

60

3

37

Navarra

79,941

1 ,682

50

81,673

89

10

1

Rioja

45,771

3,564

49,335

66

29

5

C. Valenciana

146,691

154,821

40,258

4,178

4,534

350,482

80

1

19

Total

2,218,291

896,840

95,156

23,499

12,144

271

3,246,201

59

24

new recharge (or capture). This transient situation can be long depending on aquifer characteristics.

With respect to the climatic cycles, in arid and semiarid countries significant recharge can occur only after a certain number of years, which may easily be from 5 to 10 years. Therefore, continuous decline in the water table during a dry spell of a few years, when recharge is low and abstraction is high, may not be representative of long-term trends. Declines in water levels should indicate the need for further analysis. In any case, declines in the water table can result in a decrease in the production of wells and in pumping costs. This economic impact can be more or less significant depending on the value of the crops obtained. For instance, in some zones of Andalusia, the value of crops in greenhouses may reach $50,000-70,000/ha/year. The water volume used is between 4000 and 6000 m3/ha. The energy needed to pump 1m3 100 m high is 0.3-0.4 kWh. If a $0.03 kWh energy cost is assumed, this means an increase in energy costs in the order or $0.01-0.02/m3.

Analyses on water irrigation costs are rather scarce. The WFD mandates that Member States should collect these and all relevant economic information related to the water services. A preliminary assessment has been done in Spain, which is mentioned by Estrela (2004). Table 13.4 compiles a few studies that have attempted to evaluate the impact of tariff increases as a result of the implementation of Article 9 of WFD.

Table 13.4 provides indication that the application of the full cost recovery (FCR) water rates may have a significant impact in farmers' rents and water demand. Yet, by no means should it be expected that the WFD would entail catastrophic results to the farming sector. This is proven by the evidence supported by the irrigation sector relying on groundwater resources. Generally, water costs are much closer to the FCR prices indicated in Table 13.4 than to the current prices of surface water. Yet, irrigation relying on surface sources will need to adopt more efficient water conveyance and application technologies.

Hydraulic year

Fig. 13.7. Temporal evolution of évapotranspiration from the water table in the Upper Guadiana basin, caused by water table depletion. (From Martinez-Cortina, 2001, as cited in Llamas et al., 2001.)

1959/60

1963/64

1967/68

1971/72

1975/76

1979/80

1983/84

1987/88

1991/92

1995/96

Hydraulic year

Fig. 13.7. Temporal evolution of évapotranspiration from the water table in the Upper Guadiana basin, caused by water table depletion. (From Martinez-Cortina, 2001, as cited in Llamas et al., 2001.)

1959/60

1963/64

1967/68

1971/72

1975/76

1979/80

1983/84

1987/88

1991/92

1995/96

Table 13.4 also shows the relevance of water conservation, resulting from FCR prices. Conventional wisdom about water demand for irrigation in Spain should be profoundly revised, in view of the likely reductions that will be achieved by better pricing.

In 2003 the Ministry for the Environment (MIMAM, 2004), in agreement with Article 5 of the WFD, did a preliminary analysis of the cost of groundwater in Spain. This preliminary analysis estimates the cost of groundwater for irrigation and for urban water supply in each of the 400 Spanish hydrogeologic units. The average groundwater irrigation cost for the whole of Spain is about $0.15/m3, but there exists a great dispersion of values from $0.04/m3 to $0.40/m3. This assessment has been done without specific field surveys, and should therefore be considered only as a preliminary approach. The analysis does not include an estimation of the average value of the crops guaranteed with the groundwater abstraction. Experience shows that in Spain the ratio between the value of the crop and the cost of groundwater irrigation is usually very small, usually smaller than 5-10%. In other words the silent revolution of groundwater intensive use is mainly driven by output markets (Llamas and Martínez-Santos, 2005a,b), and will not be deterred by the increasing pumping costs of lower water tables.

A significant fact is that a large sea water desalination plant (40 million cubic metres per year) has been completed in Almería (south Spain) in 2004. The main use of this treated water was supposed to be greenhouse irrigation. The price of this desalinated sea water offered by the government to the farmers is in the order of $0.40/m3. This is a political price subsidized by the EU and by the Spanish Government. The real cost might be about double. The farmers are reluctant now to accept the price of $0.40/m3, although in that area the value of the greenhouse crops obtained is in the order of $60,000/ha/year and the cost of the necessary 4000-6000 m3/ha/year would be smaller than $2000-3000/ha/year or less than 5% of the crop value. Probably the main reason for their reluctance is that in some cases they can buy or obtain groundwater at an even lower price. They do not care about the right to abstract such groundwater because, as it has been previously stated, the administrative and legal situation of groundwater rights is usually chaotic; in other words, most of the water wells in operation are illegal and the government is unable to control them. The preliminary economic analyses in the Jucar basin (Estrela, 2004) seem to confirm that the market drives the silent revolution of groundwater intensive use. For instance, in the small aquifer Crevillente in that basin, farmers are pumping their groundwater from a depth of almost 500 m at a cost of $0.40/m3. They grow special grapes for export with a value of about $20,000-30,000/ha. They use groundwater at about 3500 m3/ha/year. Therefore the ratio of groundwater irrigation cost to the crop is less than 5%. The sustain-ability of this groundwater abstraction is not threatened by the groundwater level depletion but because of groundwater quality degradation.

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