In this paper we assess the economic impact of evaporation losses from great dams (GDs) and on-farm agricultural water reservoirs (AWRs) in the semi-arid Segura River basin, SE Spain. Evaporation losses from water reservoirs reduce the high water use efficiency reached in agriculture by means of other techniques such as well-built water pipes or drip irrigation and have a substantial economic impact. Evaporation losses have been calculated using Class-A pan evaporation data and pan coefficients, whereas their economic impact has been assessed using an economic mathematical programming model that simulates land and water allocation in the different irrigated areas of the basin. Our results show that annual evaporation from GDs and AWRs represents 8.7% of the water currently available for irrigation in the Segura basin. The economic impact of such losses has been estimated in a reduction of 6.3% of the value of agricultural production and 5.4% of the farm net margin. As less water is effectively available for farmers the basin's irrigated area is reduced in a 7.5%. This impact is greater, in both absolute and relative terms, in the areas accommodating the most intensive and profitable irrigated agriculture. The applied methodology and results could be useful to regional water agencies and collective irrigation schemes for future planning and management, including the assessment of alternatives for reducing evaporation from reservoirs.
El valor de uso del agua en el regadío de la cuenca del Segura y en las zonas regables del trasvase Tajo-SeguraJavier Calatrava 1 y David Martínez-Granados 1 1 Departamento de Economía de la Empresa, ETSIA, Universidad Politécnica de Cartagena.Agradecimientos: Los autores agradecen sus valiosos comentarios a dos revisores anónimos. Parte de la información técnico-económica utilizada en el modelo ha sido financiada a través del Proyecto con referencia AGL2006-12293-C02-02/AGR. Durante parte de la realización de esta investigación, David Martínez Granados disfrutó de una beca pre-doctoral financiada con cargo al proyecto europeo IRRIQUAL (STREP FOOD-023120). Dirigir correspondencia a: Javier Calatrava Leyva. E-mail: j.calatrava@upct.es.Recibido en febrero de 2011. Aceptado en septiembre de 2011.RESumEn: Este trabajo analiza el valor económico de uso del agua en la agricultura de regadío de la Cuenca del Segura y en las zonas regables que utilizan recursos procedentes del trasvase Tajo-Segura, para lo que se emplea un modelo de programación matemática no lineal que asigna los recursos hídricos y la superficie regable entre los cultivos de cada una de las 64 Unidades de Demanda Agraria de la cuenca. Los valores marginal y medio del agua obtenidos para el conjunto de la cuenca son 0,52 €/m 3 y 0,81 €/m 3 respectivamente, si bien existen notables diferencias entre zonas. El regadío de la cuenca genera una rentabilidad media privada, medida en términos de margen neto de las explotaciones, de 879 millones de €/año, mientras que el valor de la aportación media anual de los recursos trasvasados desde la cabecera del Tajo se ha estimado en 169 millones de euros.
PALABRAS CLAVES:Economía del agua, valoración económica del agua, uso agrario del agua, programación matemática positiva.Clasificación JEL: Q25, C61.
The use value of water in the irrigated agriculture of the Segura basin and in the irrigated areas of the Tajo-Segura transfer (SE Spain)ABSTRACT: This study calculates the use value of water in the irrigated agriculture of the Segura basin and in the irrigated areas served from the Tajo-Segura transfer. Water is valued using a non-linear mathematical programming model that allocates water and irrigated land among crop activities in each of the 64 Water Demand Units of the basin. The marginal and average value of water for the basin are 0,52 €/m 3 and 0,81 €/m 3 respectively, with marked differences between areas. Irrigation in the Segura basin generates an average annual farm net margin of 879 million €/year, whereas the average annual value of resources transferred from the Tajo basin has been conservatively estimated at 169 million Euros.
The Segura basin in southeastern Spain is one of the most waterscarce regions in Europe. Its water economy has characteristics that constitute very favourable conditions for water market activity, and there are significant trading opportunities. However, the traded volumes have been rather small even though most of the water market activity in continental Spain is concentrated there. This paper describes the few formal water market experiences in the Segura basin since water trading was legislated on and regulated in 1999. As a result of this analysis, some hypotheses are made regarding the causes of the limited operation of this economic instrument.
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