The water footprint and virtual water exports of Spanish tomatoes

18 THE WATER FOOTPRINT OF TOMATO PRODUCTIONplanted in early September and harvested from Decemberuntil May or June. For the calculations theplanting date was assumed to be the 1 st of Septemberwith a growing period of 240 days (Table 2).The soils used in the case of greenhouse production whereassumed to be the same as in open-air production, exceptfor the cases of Almería, Granada and the two provinces inthe Canary Islands, since in these provinces, most of thegreenhouse production is done on artificial soils. These soilsare constructed by extending a layer of 2 cm deep of manure,clay and sand mulch above them. The parameters ofthese soils were obtained from the study of F.I.A.P.A. Foundation(Foundation for Agricultural Research in eh Provinceof Almería) on the soils of greenhouses in the Poniente regionof Almería province (Gil de Carrasco, 2001), and fromBertuglia (2008) for the province of Granada. In the CanaryIslands, the production is carried out also in a wide rangeof soils: natural, (local or transported) modified natural soilsor artificial (Nuez, 1995).The atmospheric demand inside the greenhouse was considered70-80% of that outside (Orgaz et al., 2005) and noprecipitation was taken into account. Many of the greenhouseshave rainwater collectors (Fernández, 2001). Mostly,rainwater harvesting refers to the collection of rain thatotherwise would become runoff. Since consumptive use ofharvested rainwater will subtract from runoff, we considersuch water use as a blue water footprint.2.3. Calculation of the water apparentproductivity and exported virtual waterThe water apparent productivity was calculated using themonthly tomato prices from the Agricultural and Statistics