Influencia de la humedad relativa y el viento en el funcionamiento de condensadores radiativos pasivos

El uso de condensadores radiativos pasivos (CRPs) parece ser una técnica adecuada para determinar y cuantificar eventos de condensación natural. En este estudio, dos CRPs se equiparon con dos films de polietileno de diferentes características físico - químicas. Uno de ellos de color blanco, tratado especialmente para favorecer la condensación y otro de color negro típicamente usado en cobertura de invernaderos. El agua condensada se recogió diariamente mediante un depósito instalado en cada CRP y se correlacionó con las principales variables meteorológicas. El CRP con el film negro recogió un 17,8 % más de condensación que el CRP con el film blanco como consecuencia de su mayor enfriamiento radiativo nocturno. Finalmente, la humedad relativa y el viento condicionaron fuertemente la formación de condensación.Asociación de Jóvenes Investigadores de Cartagena, (AJICT). Universidad Politécnica de Cartagena. Escuela Técnica Superior de Ingeniería Industrial UPCT, (ETSII). Escuela Técnica Superior de Ingeniería Agronómica, (ETSIA), Escuela Técnica Superior de Ingeniería de Telecomunicación (ETSIT). Escuela de Ingeniería de Caminos, Canales, y Puertos y de Ingeniería de Minas, (EICM). Fundación Séneca, Agencia Regional de Ciencia y Tecnología. Parque Tecnológico de Fuente Álamo. Grupo Aquilin

Comparative analysis of two polyethylene foil materials for dew harvesting in a semi-arid climate

This paper analyses the dew collection performance of two polyethylene (PE) foils in a semi-arid region (Southern Spain). The dew collecting devices consisted of two commercial passive radiative dew condensers (RDCs) of 1 m2 tilted to 30°. They were fitted with two different high-emissivity PE foils: a white hydrophilic foil (WSF) recommended as standard for dew recovery comparisons by the International Organization for Dew Utilization (OPUR), and a low-cost black PE foil (BF) widely used for mulching in horticulture. Dew yield, foil surface temperature and meteorological variables (air temperature, relative humidity, downward long wave radiation and wind speed) were recorded hourly during a 1-year period from May-2009 to May-2010. The spectral emissivity of the foils was determined in laboratory in the range 2.5–25 μm and the radiance-weighed values were calculated over different intervals, indicating that BF emitted more than WSF, especially in the range 2.5–7 μm. Dew yield was well correlated with the air relative humidity and foil net radiation in both foils and was hardly detected when the relative humidity was lower than 75% or the wind speed higher than 1.5 m s−1. WSF was more sensitive to dew formation due to its hydrophilic properties, registering more dewy nights (175) than BF (163) while the annual cumulative dew yield for BF was higher (20.76 mm) than for WSF (17.36 mm) due to the higher emissivity and emitted radiance of BF. These results suggested that increasing the surface emissivity over the whole IR spectrum could be more effective for improving RDC yield performances than increasing the surface hydrophilic properties. On a practical point of view, BF could be considered as a suitable material for large scale RDCs, as in our study it presented several advantages over the reference material, such as higher dew collection performance, longer lifespan and much lower cost.The authors acknowledge the Foundation Seneca (Murcia, Spain) and the Ministry of Science and Innovation for the financial support of this study through the grants 02978/PI/05 and AGL2010-15001 respectively

Energy balance and evaporation loss of an irrigation reservoir equipped with a suspended cover in a semiarid climate (south-eastern Spain)

The main objective of this study was to assess the impact of a suspended cover on the evaporation loss of an agricultural water reservoir (AWR). To this aim, a detailed data collection was carried out in a typical AWR located in south-eastern Spain during 2 consecutive years. During the first year, the reservoir remained uncovered, while during the second year it was covered with a double black polyethylene (PE) shade cloth. On an annual scale, it was observed that the cover can provide a reduction of evaporation loss of 85%. Two approaches, energy balance and mass transfer, were used to analyse the effect of the cover on the evaporation process. Important modifications were observed on the magnitude, sign, annual trend and relative weight of the components of the energy balance. The changes were ascribed to the strong reduction of net radiation and to the substantial weight of the heat storage and sensible heat flux in the energy balance. A relevant finding was the contrast between the patterns of the annual evaporation curve for open-water and covered conditions. The mass transfer approach allowed discriminating between the wind-and radiation-shelter effects on the evaporation term. The reduction in water-to-air vapour deficit was the main factor explaining the high efficiency of the cover, whereas the reduction of the mass transfer coefficient was a modulating factor that accounted for the wind-shelter effect. Overall, both approaches provided a sound basis to describe and explain the physical mechanisms underlying the high performance of the tested cover.The authors acknowledge the Fundación Séneca (Murcia, Spain) and the Ministerio de Educación y Ciencia (Spain) for the financial support of this study through the grants 02978/PI/05 and 11051/AC/09 and PET2005_0056 respectively

Evaluation of evaporation estimation methods for a covered reservoir in a semi-arid climate (south-eastern Spain)

The main purpose of this study was to evaluate different methods of evaporation estimation for covered water reservoirs. A reservoir equipped with a suspended cover was fully monitored to register the evaporation rate and microclimate below the cover. The datasets were used to evaluate the performance of commonly used evaporation methods, namely energy budget, mass-transfer, combination (Penman and FAO-56 Penman-Monteith) and floating class-A pan. The mass-transfer formula based on the Sherwood number proposed for free convection conditions, which were observed to prevail below the cover, supplied reasonably good estimates of covered reservoir evaporation and it is a good option from a practical point of view, with low input data requirements. Detailed input data and modifications in the calculation of energy fluxes are required to get good evaporation estimations of covered surfaces with the energy budget and FAO-56 Penman-Monteith methods. Besides, some of the standard meteorological input data (such as wind speed at 2 m height) cannot be registered below the cover. Penman equation presented a poor performance related to the overestimation of the advective component for free convection conditions. The pan evaporation was found to be substantially higher than the reservoir evaporation, due to the particular characteristics of the tank, that increased surface temperature and hence evaporation rate. A simplified empirical mass-transfer formula was also proposed to estimate evaporation of covered water bodies from the only knowledge of the surface-to-air mixing ratio gradient.The authors acknowledge the Ministerio de Ciencia e Innovación (Spain) and FEDER (Fondo Europeo de Desarrollo Regional) for the financial support of this study through the grant AGL2010-15001

Irriblend-DSW: A decision support tool for the optimal blending of desalinated and conventional irrigation waters in dry regions

Desalinated sea water (DSW) is increasingly being used as an alternative source of irrigation in dry coastal areas. Owing to its high price and singular composition, it is often blended with other water resources to curb costs. Although this is a common practice, limited resources are available to manage the increased agro-economic complexity required to balance several water sources with heterogeneous quality, price, and availability restrictions. To support the management of fertigation with DSW, in this study, we present an open-source decision support tool (DST), Irriblend-DSW. The DST has been designed to identify potentially profitable fertigation options for different water and fertiliser availability scenarios. To demonstrate the key features of the tool, we applied it to two actual case study scenarios in south-eastern Spain, where severe water scarcity led to massive seawater desalination for agricultural supply. The information provided by the DST enabled the assessment of the viability of different water blending options and the selection of an optimal combination of water and fertilisers. The simulation results showed that the fertigation costs of the studied crops, hydroponic lettuce, and greenhouse tomato substantially increased with the integration of DSW. The DST output showed how water price rises, and how additional types and amounts of fertilisers are required when more DSW is used. However, because the salinity of the blend is also reduced with the use of DSW, the yield outcome improves and, thus, to some extent, compensates for the increased cost. In fact, despite higher costs, the studied crops were found to be very profitable when the optimised solutions computed by the DST were selected. Moreover, the optimum fertigation solutions not only reduced costs but also decreased nutrient leaching in areas of severely polluted aquifers.This study was supported by the Ministerio de Economía, Industria y Competitividad (MINECO, Spain), the Agencia Estatal de Investigación (AEI, Spain), and the Fondo Europeo de Desarrollo Regional (FEDER, Europe), which funded the project RIDESOST (AGL2017-85857-C2-1-R and AGL2017-85857-C2–2-R). Additional support was provided by the European Commission (Europe) (grant LIFE16 ENV/ES/000341, DESEACROP Project). The collaboration of Cátedra Trasvase y Sostenibilidad – Jose Manuel Claver Valderas is also acknowledged. B. Gallego-Elvira acknowledges support from the Ministry of Science, Innovation and University of Spain (“Beatriz Galindo” Fellowship BEAGAL18/00081)

Producing lettuce in soil-based or in soilless outdoor systems. Which is more profitable?

[SPA] Este trabajo presenta una evaluación económica de dos sistemas de producción de lechuga, Cultivo en Suelo (CS) y Técnica de Película Nutritiva (TPN). En el sistema TPN, el rendimiento, la productividad del agua, el costo total, los ingresos y el beneficio fueron 5.5, 2.6, 6.2, 5.7 y 3.1 veces superior que en el sistema CS, respectivamente. La evaluación financiera mostró un valor presente neto en el sistema TPN 3.1 veces superior que el sistema CS, sin embargo, la tasa interna de retorno en el sistema CS fue 4 veces superior que en el sistema TPN. En este sentido, los mayores costos operacionales y de inversión en el sistema TPN permiten una menor proporción de ganancias/costos totales (0.079 contra 0.134). [ENG] This work presents an economic assessment of two lettuce production systems, soil cultivation (SC) and nutrient film technique (NFT). In the NFT system, the yield, the water productivity, the total cost, the revenue and the profit were 5.5, 2.6, 6.2, 5.7 and 3.1 times higher than in the SC system, respectively. The financial assessment showed a net present value in the NFT system 3.1 times higher than in the SC system, however, the internal rate of return in the SC system was 4 times higher than in the NFT system. In this sense, the higher investment and operational costs in the NFT system led to a lower ratio of profit/total costs (0.079 versus 0.134).Fundación Séneca – Agencia de Ciencia y Tecnología de la Región de Murcia [19280/PI/14] y la Comisión Europea (LIFE16 ENV/ES/000341, DESEACROP Project) por su apoyo

Characterization of the agricultural supply of desalinated seawater in Southeastern Spain

The increasing shortage of water for crop irrigation in arid and semiarid regions is encouraging the use of non-conventional resources. In the last decade, seawater desalination has consolidated its position as an alternative source to increase the supply for agricultural irrigation in Spain and Israel, where the farmers’ acceptance is progressively rising, despite the supply price being much higher than that of other conventional water sources. This article describes the current situation of desalinated seawater production and supply to agriculture in the southeast of Spain, and analyzes key questions such as its role in regional water planning, the infrastructure needed for conveyance and distribution, the energy requirements, the production and distribution costs, and the final price to farmers. The study is based on descriptive and quantitative data collected from desalination plants and irrigation district managers through technical questionnaires and personal interviews. The results show how seawater desalination is effectively alleviating the regional constraints in the irrigated agriculture supply, and why it is becoming strategic to maintaining food production and socioeconomic development. However, the high-energy requirements and associated costs in comparison with other water sources limit a more widespread use for agriculture, and for this reason desalinated water still only plays a complementary role in most irrigation districts.The authors would like to thank all the desalination plants and the irrigation district managers for providing the data on which the study has been carried out. The collaboration of partners in DESEACROP Project (Universidad de Almería, Valoriza Agua, and Comunidad de Usuarios de Aguas de la Comarca de Nijar) is also acknowledged

Recycling drainage effluents using reverse osmosis powered by photovoltaic solar energy in hydroponic tomato production: Environmental footprint analysis

Greenhouse cultivation in the Mediterranean region has undoubtedly enhanced the economic growth and has generated social benefits by making an efficient use of resources. However, these production systems caused undesirable environmental impacts. In order to move towards cleaner production in greenhouse areas, this study has assessed the potential environmental benefits and trade-offs of the integration of an on-farm reverse osmosis system powered by photovoltaic solar energy to recycle the drainage effluents from greenhouses. To that end, we compare the environmental footprint of a greenhouse tomato crop using this technology in a hydroponic system (HS), versus the conventional sanded soil ‘enarenado’ (CS) with free-drainage to soil. Additionally, for comparison, three independent irrigation sources (desalinated seawater with low electrical conductivity and two different mixes of underground and desalinated water, with moderate and high electrical conductivity, respectively) were evaluated. The use of desalinated seawater can help reduce the overexploitation of aquifers, although if the desalination process is not done with clean energy it also comes with a negative impact on the carbon footprint. Life Cycle Assessment (LCA) was used to analyse and evaluate six environmental impact indicators associated with these production systems and water treatments. In addition, a sensitivity analysis was conducted to explore the potential environmental benefits of increasing the use of renewable energy for desalinated water production, whilst also curbing the common over-fertilisation malpractice reported in the study area. Based on our findings, the HS with leachate treatment technology showed, compared to the CS system, a significant reduction in the eutrophication (72 %), although it did inevitably increase the depletion of fossil fuels (43 %) global warming (37 %) and acidification (32 %) impacts, due to the need for additional infrastructure and equipment. Among the inputs considered for the cultivation systems, the greenhouse structure, and the production of fertilisers and electricity for fertigation represented the highest environmental burdens. When comparing the three irrigation treatments, it was observed that the partial substitution of desalinated seawater by brackish groundwater substantially mitigated (27 %) the global warming footprint. The sensitivity analysis revealed that a significant reduction in the environmental impact is feasible.This study was funded by the LIFE Program of the European Union through the DESEACROP project (LIFE16-ENV-ES-000341). Gallego-Elvira acknowledges the support from The Ministry of Science, Innovation and University (“Beatriz Galindo” Fellowship BEAGAL18/00081)

Implementación en el espacio de usuario del protocolo de encaminamiento AODVv2

El protocolo AODV es un protocolo reactivo de encaminamiento para redes MANET que se utiliza frecuentemente como referencia tanto para desarrollar nuevos protocolos de encaminamiento en redes ad hoc como para evaluar su rendimiento. Aunque el protocolo está presente en varios simuladores de red (por ejemplo, ns2, OMNeT++, etc.), existen pocas implementaciones que puedan emplearse en condiciones reales para la investigación de campo o de evaluación. Este documento presenta una implementación en el espacio de usuario de la última versión del protocolo, el AODVv2, que se puede utilizar en cualquier dispositivo capaz de ejecutar Linux. El objetivo del proyecto ha sido el desarrollo de una implementación de AODVv2 de codigo abierto y fácil mantenimiento, para ser utilizada con fines experimentales por la comunidad científica. El presente documento proporciona una descripción de los principales criterios de diseño y codificación considerados para implementar el protocolo, y expone además las principales pruebas que se han realizado con el fin de verificar su correcto funcionamiento.Postprint (published version

Balance de carbono de las zonas regables del trasvase Tajo-Segura

[SPA] La demarcación hidrográfica del Segura se caracteriza por presentar un importante déficit estructural de agua, que afecta fundamentalmente al regadío, ya que se trata del uso con mayor demanda y se considera de menor prioridad que el suministro a poblaciones. La incorporación de Agua Marina Desalinizada (AMD) es una de las principales estrategias para hacer frente al persistente déficit hídrico que afecta al regadío del sureste español. Con el fin de mejorar el conocimiento sobre la sostenibilidad de la agricultura que se desarrolla en las Zonas Regables del Trasvase Tajo-Segura, en este trabajo se estima la huella de carbono de estos regadíos, para tres escenarios de incremento de AMD. Se realiza el balance de carbono como diferencia entre las emisiones de Gases de Efecto Invernadero (GEI) de las actividades agrícolas, y la remoción de CO2 asociada a los cultivos implantados. Los resultados globales indican que los regadíos del trasvase Tajo-Segura (TTS) representan un importante sumidero de carbono en cualquiera de los escenarios analizados, disminuyendo su capacidad como sumidero de carbono conforme se intensifica la energía específica del suministro de agua de riego, variando de -1.208.084 t CO2/año en el Escenario Concesional hasta -707.276 t CO2/año en Escenario de Sustitución del TTS por desalación, pasando por -1.081.080 t CO2/año en el Escenario Actual. La progresiva sustitución de agua del TTS por AMD reduciría en un 30% la capacidad de ser sumidero de CO2 de la agricultura. Los resultados por cultivos muestran que todos los cultivos son sumideros de CO2, siendo los leñosos 9 veces más eficientes que los hortícolas. Las UDAs en las que predominan los cultivos hortícolas serían las más perjudicadas por la sustitución de TTS por AMD. [ENG] The Segura river basin is characterized by a structural water deficit, which fundamentally affects irrigation, since it is the use with the highest demand and considered to be of lower priority than the urban supply. The use of desalinated sea water (DSW) is one of the main strategies to deal with the persistent water deficit that affects irrigated agriculture in south-east Spain. In order to improve the knowledge about the sustainability of crops in the Tajo-Segura Irrigated area, this study evaluates the carbon footprint (CF) of the main crops in the area for three scenarios with increasing DSW. The CF was obtained as difference between the greenhouse gas emissions (GHG) of agricultural activities, and the CO2 fixed by crops. Overall, the results show that Tajo-Segura irrigation area represents an important carbon sink in all scenarios, and that the carbon sink capacity is reduced when the specific energy of the irrigation water supply intensifies, varying from -1,208,084 t CO2/year in the Concessional Scenario up to -707,276 t CO2/year in the TTS water substitution for DSW Scenario, going through -1,081,080 t CO2/year in the Current Scenario. The progressive replacement of TTS water by DSW could potentially reduce CO2 sink capacity of agriculture by 30%. The results show that all crops are CO2 sinks, but the woody crops are 9 times more efficient tan horticultural crops. Therefore, the UDAs in which horticultural crops dominate are expected to be affected the most by the replacement of TTS water by DSW.Las distintas actividades necesarias para el desarrollo de este trabajo han sido financiadas por (1) el Ministerio de Economía y Competitividad y el Fondo Europeo de Desarrollo Regional a través del proyecto RIDESOST (AGL2017-85857-C2-2-R), y (2) por la Cátedra Universidad-Empresa “Trasvase y Sostenibilidad – José Manuel Claver Valderas”, creada por el Sindicato Central de Regantes del Acueducto Tajo-Segura (SCRATS) y la Universidad Politécnica de Cartagena (UPCT)