848 resultados para semi-arid savanna


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A participatory modelling process has been conducted in two areas of the Guadiana river (the upper and the middle sub-basins), in Spain, with the aim of providing support for decision making in the water management field. The area has a semi-arid climate where irrigated agriculture plays a key role in the economic development of the region and accounts for around 90% of water use. Following the guidelines of the European Water Framework Directive, we promote stakeholder involvement in water management with the aim to achieve an improved understanding of the water system and to encourage the exchange of knowledge and views between stakeholders in order to help building a shared vision of the system. At the same time, the resulting models, which integrate the different sectors and views, provide some insight of the impacts that different management options and possible future scenarios could have. The methodology is based on a Bayesian network combined with an economic model and, in the middle Guadiana sub-basin, with a crop model. The resulting integrated modelling framework is used to simulate possible water policy, market and climate scenarios to find out the impacts of those scenarios on farm income and on the environment. At the end of the modelling process, an evaluation questionnaire was filled by participants in both sub-basins. Results show that this type of processes are found very helpful by stakeholders to improve the system understanding, to understand each others views and to reduce conflict when it exists. In addition, they found the model an extremely useful tool to support management. The graphical interface, the quantitative output and the explicit representation of uncertainty helped stakeholders to better understand the implications of the scenario tested. Finally, the combination of different types of models was also found very useful, as it allowed exploring in detail specific aspects of the water management problems.

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This study reports the results of a water footprint (WF) assessment of five types of textiles commonly used for the production of jeans, including two different fibres (cotton and Lyocell fibre) and five corresponding production methods for spinning, dyeing and weaving. The results show that the fibre production is the stage with the highest water consumption, being cotton production particularly relevant. Therefore, the study pays particular attention to the water footprint of cotton production and analyses the effects of external factors influencing the water footprint of a product, in this case, the incentives provided by the EU Common Agricultural Policy (CAP), and the relevance of agricultural practices to the water footprint of a product is emphasised. An extensification of the crop production led to higher WF per unit, but a lower overall pressure on the basins water resources. This study performs a sustainability assessment of the estimated cotton WFs with the water scarcity index, as proposed by Hoekstra et al. (2011), and shows their variations in different years as a result of different water consumption by crops in the rest of the river basin. In our case, we applied the assessment to the Guadalquivir, Guadalete and Barbate river basins, three semi-arid rivers in South Spain. Because they are found to be relevant, the available water stored in dams and the outflow are also incorporated as reference points for the sustainability assessment. The study concludes that, in the case of Spanish cotton production, the situation of the basin and the policy impact are more relevant for the status of the basin s water resources than the actual WF of cotton production. Therefore, strategies aimed at reducing the impact of the water footprint of a product need to analyse both the WF along the value chain and within the local context.

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The biogeochemical cycles of carbon (C), nitrogen (N) and phosphorus (P) are interlinked by primary production, respiration and decomposition in terrestrial ecosystems. It has been suggested that the C, N and P cycles could become uncoupled under rapid climate change because of the different degrees of control exerted on the supply of these elements by biological and geochemical processes. Climatic controls on biogeochemical cycles are particularly relevant in arid, semi-arid and dry sub-humid ecosystems (drylands) because their biological activity is mainly driven by water availability. The increase in aridity predicted for the twenty-first century in many drylands worldwide may therefore threaten the balance between these cycles, differentially affecting the availability of essential nutrients. Here we evaluate how aridity affects the balance between C, N and P in soils collected from 224 dryland sites from all continents except Antarctica. We find a negative effect of aridity on the concentration of soil organic C and total N, but a positive effect on the concentration of inorganic P. Aridity is negatively related to plant cover, which may favour the dominance of physical processes such as rock weathering, a major source of P to ecosystems, over biological processes that provide more C and N, such as litter decomposition. Our findings suggest that any predicted increase in aridity with climate change will probably reduce the concentrations of N and C in global drylands, but increase that of P. These changes would uncouple the C, N and P cycles in drylands and could negatively affect the provision of key services provided by these ecosystems.

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There is a need for in-situ soil moisture conservation in arid and semi-arid regions due to insufficient rainfall for agriculture. For this purpose, a combination implement [integrated reservoir tillage system (RT)] comprised of a single-row chisel plow, single-row spike tooth harrow, modified seeder, and spiked roller was developed and compared to the popular tillage practices, viz., minimum tillage (MT) and conventional tillage (CT) in an arid Mediterranean environment in Egypt. The different tillage practices were conducted at tillage depths of 15, 20, and 25 cm and forward speeds of 0.69, 1, 1.25, and 1.53 m s-1. Some soil physical properties, runoff, soil loss, water harvesting efficiency and yield of wheat were evaluated. The different tillage practices caused significant differences in soil physical properties as the RT increased soil infiltration, producing a rate of 48% and 65% higher than that obtained in MT and CT, respectively. The lowest values of runoff and soil loss were recorded under RT as 4.91 mm and 0.65 t ha-1, whereas the highest values were recorded under CT as 11.36 mm and 1.66 t ha-1, respectively. In conclusion, the RT enhanced the infiltration rate, increased water harvesting efficiency, reduced runoff and achieved the highest yield of wheat. The best tillage operating parameters appeared to be at a tillage depth of 20 cm and speed between 1.00 and 1.25 m s-1.

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In the last decade, research on irrigation has mainly been aimed at reducing crop water consumption. In arid and semi-arid environments, in relation to the limited water resources, the use of low quality water in agriculture has also been investigated in order to detect their effects on soil physical properties and on crop production. More recently, even the reduction of energy consumption in agriculture, as well as the effects of external factors, climate change and agricultural policies, have been major research interests. All these objectives have been considered in the papers included in this special issue. However, in the last years, approaches aimed at reducing crop water requirements have significantly changed. Remote sensing with satellites or unmanned vehicles, and vegetation spectral measurements, among others, represent in fact the newest frontier of existing technologies. Knowledge of soil hydraulic properties, often forgotten because of the difficulty of their estimation, can also be considered as a new way to reduce water consumption.

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Irrigated agricultural landscapes generate a valuable set of ecosystem services, which are threatened by water scarcity in many aridand semi‐arid regions of the world. In the Mediterranean region, climate change is expected to decrease water availability through reduced precipitation and more frequent drought spells. At the same time, climate change, demographic and economic development and an agricultural sector highly dependent on irrigation, will raise water demand, increasing experienced water scarcity and affecting the provision of ecosystem services from water resources and agro-ecosystems. In this context, policy makers face the challenge of balancing the provision of different ecosystem services, including agricultural income and production and also water ecosystem protection.

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Evaluate a set of agricultural adaptation strategies to cope with climate change impacts, with focus on the consequences of extreme events on the adaptations proposed in the semi-arid environment of Andalusia (Southern Spain).

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Las alteraciones del sistema climático debido al aumento de concentraciones de gases de efecto invernadero (GEI) en la atmósfera, tendrán implicaciones importantes para la agricultura, el medio ambiente y la sociedad. La agricultura es una fuente importante de emisiones de gases de efecto invernadero (globalmente contribuye al 12% del total de GEI), y al mismo tiempo puede ser parte de la solución para mitigar las emisiones y adaptarse al cambio climático. Las acciones frente al desafío del cambio climático deben priorizar estrategias de adaptación y mitigación en la agricultura dentro de la agenda para el desarrollo de políticas. La agricultura es por tanto crucial para la conservación y el uso sostenible de los recursos naturales, que ya están sometidos a impactos del cambio climático, al mismo tiempo que debe suministrar alimentos para una población creciente. Por tanto, es necesaria una coordinación entre las actuales estrategias de política climática y agrícola. El concepto de agricultura climáticamente inteligente ha surgido para integrar todos estos servicios de la producción agraria. Al evaluar opciones para reducir las amenazas del cambio climático para la agricultura y el medio ambiente, surgen dos preguntas de investigación: • ¿Qué información es necesaria para definir prácticas agrarias inteligentes? • ¿Qué factores influyen en la implementación de las prácticas agrarias inteligentes? Esta Tesis trata de proporcionar información relevante sobre estas cuestiones generales con el fin de apoyar el desarrollo de la política climática. Se centra en sistemas agrícolas Mediterráneos. Esta Tesis integra diferentes métodos y herramientas para evaluar las alternativas de gestión agrícola y políticas con potencial para responder a las necesidades de mitigación y adaptación al cambio climático. La investigación incluye enfoques cuantitativos y cualitativos e integra variables agronómicas, de clima y socioeconómicas a escala local y regional. La investigación aporta una recopilación de datos sobre evidencia experimental existente, y un estudio integrado sobre el comportamiento de los agricultores y las posibles alternativas de cambio (por ejemplo, la tecnología, la gestión agrícola y la política climática). Los casos de estudio de esta Tesis - el humedal de Doñana (S España) y la región de Aragón (NE España) - permiten ilustrar dos sistemas Mediterráneos representativos, donde el uso intensivo de la agricultura y las condiciones semiáridas son ya una preocupación. Por este motivo, la adopción de estrategias de mitigación y adaptación puede desempeñar un papel muy importante a la hora de encontrar un equilibrio entre la equidad, la seguridad económica y el medio ambiente en los escenarios de cambio climático. La metodología multidisciplinar de esta tesis incluye una amplia gama de enfoques y métodos para la recopilación y el análisis de datos. La toma de datos se apoya en la revisión bibliográfica de evidencia experimental, bases de datos públicas nacionales e internacionales y datos primarios recopilados mediante entrevistas semi-estructuradas con los grupos de interés (administraciones públicas, responsables políticos, asesores agrícolas, científicos y agricultores) y encuestas con agricultores. Los métodos de análisis incluyen: meta-análisis, modelos de gestión de recursos hídricos (modelo WAAPA), análisis multicriterio para la toma de decisiones, métodos estadísticos (modelos de regresión logística y de Poisson) y herramientas para el desarrollo de políticas basadas en la ciencia. El meta-análisis identifica los umbrales críticos de temperatura que repercuten en el crecimiento y el desarrollo de los tres cultivos principales para la seguridad alimentaria (arroz, maíz y trigo). El modelo WAAPA evalúa el efecto del cambio climático en la gestión del agua para la agricultura de acuerdo a diferentes alternativas políticas y escenarios climáticos. El análisis multicriterio evalúa la viabilidad de las prácticas agrícolas de mitigación en dos escenarios climáticos de acuerdo a la percepción de diferentes expertos. Los métodos estadísticos analizan los determinantes y las barreras para la adopción de prácticas agrícolas de mitigación. Las herramientas para el desarrollo de políticas basadas en la ciencia muestran el potencial y el coste para reducir GEI mediante las prácticas agrícolas. En general, los resultados de esta Tesis proporcionan información sobre la adaptación y la mitigación del cambio climático a nivel de explotación para desarrollar una política climática más integrada y ayudar a los agricultores en la toma de decisiones. Los resultados muestran las temperaturas umbral y la respuesta del arroz, el maíz y el trigo a temperaturas extremas, siendo estos valores de gran utilidad para futuros estudios de impacto y adaptación. Los resultados obtenidos también aportan una serie de estrategias flexibles para la adaptación y la mitigación a escala local, proporcionando a su vez una mejor comprensión sobre las barreras y los incentivos para su adopción. La capacidad de mejorar la disponibilidad de agua y el potencial y el coste de reducción de GEI se han estimado para estas estrategias en los casos de estudio. Estos resultados podrían ayudar en el desarrollo de planes locales de adaptación y políticas regionales de mitigación, especialmente en las regiones Mediterráneas. ABSTRACT Alterations in the climatic system due to increased atmospheric concentrations of greenhouse gas emissions (GHG) are expected to have important implications for agriculture, the environment and society. Agriculture is an important source of GHG emissions (12 % of global anthropogenic GHG), but it is also part of the solution to mitigate emissions and to adapt to climate change. Responses to face the challenge of climate change should place agricultural adaptation and mitigation strategies at the heart of the climate change agenda. Agriculture is crucial for the conservation and sustainable use of natural resources, which already stand under pressure due to climate change impacts, increased population, pollution and fragmented and uncoordinated climate policy strategies. The concept of climate smart agriculture has emerged to encompass all these issues as a whole. When assessing choices aimed at reducing threats to agriculture and the environment under climate change, two research questions arise: • What information defines smart farming choices? • What drives the implementation of smart farming choices? This Thesis aims to provide information on these broad questions in order to support climate policy development focusing in some Mediterranean agricultural systems. This Thesis integrates methods and tools to evaluate potential farming and policy choices to respond to mitigation and adaptation to climate change. The assessment involves both quantitative and qualitative approaches and integrates agronomic, climate and socioeconomic variables at local and regional scale. The assessment includes the collection of data on previous experimental evidence, and the integration of farmer behaviour and policy choices (e.g., technology, agricultural management and climate policy). The case study areas -- the Doñana coastal wetland (S Spain) and the Aragón region (NE Spain) – illustrate two representative Mediterranean regions where the intensive use of agriculture and the semi-arid conditions are already a concern. Thus the adoption of mitigation and adaptation measures can play a significant role for reaching a balance among equity, economic security and the environment under climate change scenarios. The multidisciplinary methodology of this Thesis includes a wide range of approaches for collecting and analysing data. The data collection process include revision of existing experimental evidence, public databases and the contribution of primary data gathering by semi-structured interviews with relevant stakeholders (i.e., public administrations, policy makers, agricultural advisors, scientist and farmers among others) and surveys given to farmers. The analytical methods include meta-analysis, water availability models (WAAPA model), decision making analysis (MCA, multi-criteria analysis), statistical approaches (Logistic and Poisson regression models) and science-base policy tools (MACC, marginal abatement cost curves and SOC abatement wedges). The meta-analysis identifies the critical temperature thresholds which impact on the growth and development of three major crops (i.e., rice, maize and wheat). The WAAPA model assesses the effect of climate change for agricultural water management under different policy choices and climate scenarios. The multi-criteria analysis evaluates the feasibility of mitigation farming practices under two climate scenarios according to the expert views. The statistical approaches analyses the drivers and the barriers for the adoption of mitigation farming practices. The science-base policy tools illustrate the mitigation potential and cost effectiveness of the farming practices. Overall, the results of this Thesis provide information to adapt to, and mitigate of, climate change at farm level to support the development of a comprehensive climate policy and to assist farmers. The findings show the key temperature thresholds and response to extreme temperature effects for rice, maize and wheat, so such responses can be included into crop impact and adaptation models. A portfolio of flexible adaptation and mitigation choices at local scale are identified. The results also provide a better understanding of the stakeholders oppose or support to adopt the choices which could be used to incorporate in local adaptation plans and mitigation regional policy. The findings include estimations for the farming and policy choices on the capacity to improve water supply reliability, abatement potential and cost-effective in Mediterranean regions.

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In crop insurance, the accuracy with which the insurer quantifies the actual risk is highly dependent on the availability on actual yield data. Crop models might be valuable tools to generate data on expected yields for risk assessment when no historical records are available. However, selecting a crop model for a specific objective, location and implementation scale is a difficult task. A look inside the different crop and soil modules to understand how outputs are obtained might facilitate model choice. The objectives of this paper were (i) to assess the usefulness of crop models to be used within a crop insurance analysis and design and (ii) to select the most suitable crop model for drought risk assessment in semi-arid regions in Spain. For that purpose first, a pre-selection of crop models simulating wheat yield under rainfed growing conditions at the field scale was made, and second, four selected models (Aquacrop, CERES- Wheat, CropSyst and WOFOST) were compared in terms of modelling approaches, process descriptions and model outputs. Outputs of the four models for the simulation of winter wheat growth are comparable when water is not limiting, but differences are larger when simulating yields under rainfed conditions. These differences in rainfed yields are mainly related to the dissimilar simulated soil water availability and the assumed linkages with dry matter formation. We concluded that for the simulation of winter wheat growth at field scale in such semi-arid conditions, CERES-Wheat and CropSyst are preferred. WOFOST is a satisfactory compromise between data availability and complexity when detail data on soil is limited. Aquacrop integrates physiological processes in some representative parameters, thus diminishing the number of input parameters, what is seen as an advantage when observed data is scarce. However, the high sensitivity of this model to low water availability limits its use in the region considered. Contrary to the use of ensembles of crop models, we endorse that efforts be concentrated on selecting or rebuilding a model that includes approaches that better describe the agronomic conditions of the regions in which they will be applied. The use of such complex methodologies as crop models is associated with numerous sources of uncertainty, although these models are the best tools available to get insight in these complex agronomic systems.

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A exibição do comportamento vocal em muitas espécies de anfíbios anuros é relacionada aos níveis de hormônios esteroides gonadais e interrenais. Esses hormônios poderiam mediar a relação entre intensidade de sinais e imunidade, pois estão envolvidos no desenvolvimento das características sexuais secundárias, comportamento de corte e mobilização de reservas energéticas durante a atividade reprodutiva, enquanto apresentam também efeitos imunomoduladores. Nesse sentido, o objetivo deste trabalho foi explorar as relações entre comportamento reprodutivo, imunidade e níveis plasmáticos de testosterona e corticosterona em machos do sapo do semiárido brasileiro, Rhinella granulosa, em atividade reprodutiva e após manipulação hormonal. A precipitação foi o principal determinante ambiental para o aumento dos níveis de testosterona e corticosterona circulantes em machos de R. granulosa, estimulando o comportamento de vocalização. As relações fisiológicas encontradas indicam que os altos níveis plasmáticos de testosterona nos primeiros dias após a chuva devem promover o início do turno vocal, porém a corticosterona deve modular o esforço de vocalização. De forma geral, a exacerbação do comportamento vocal de R. granulosa tem efeitos negativos sobre a imunocompetência, porém alguns indivíduos que apresentam maiores concentrações plasmáticas de corticosterona apresentam concomitantemente alto esforço vocal e alta imunidade. De acordo, a aplicação transdérmica de corticosterona promoveu elevação aguda dos níveis plasmáticos deste glicocorticoide, bem como um aumento da função imune. Assim, apesar de a atenção principal ser comumente colocada no papel da testosterona na mediação de sinais honestos, nossos resultados corroboram a importância da corticosterona na mediação da expressão do comportamento de corte e imunocompetência em machos R. granulosa

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No semiárido brasileiro, a vegetação predominante é a Caatinga, bioma ainda pouco explorado, que apresenta plantas e micro-organismos com alta resistência aos períodos de seca imposto pelo clima. Os micro-organismos associados às plantas deste bioma, são capazes de desenvolver mecanismos de proteção celular contra o estresse hídrico, assim como proteção vegetal contra a dessecação. O presente estudo buscou compreender as rizobactérias associadas a Mimosa artemisiana a fim de selecionar bactérias tolerantes à seca com características de promover o crescimento de plantas sob condições de estresse hídrico, diminuindo assim, os efeitos adversos impostos pela seca. As amostras de solo rizosférico foram coletadas ao longo da Caatinga, englobando os estados da BA e PE, totalizando quatro pontos de coleta. Com o uso de metodologias dependentes de cultivo, foi isolado bactérias com algumas características de promoção de crescimento de plantas diretos e/ou indiretos, como produção de AIA e fixação de nitrogênio. Além disso, linhagens capazes de crescer em meio com reduzida atividade de água e com mecanismos de proteção contra a dessecação, como, produção de EPS, biofilme, produção da ACC deaminase e indução de resistência sistêmica através das enzimas peroxidase e polifenoloxidase. Uma linhagem de Paenibacillus sp. e outra de Bacillus sp. foram capazes de promover o crescimento de soja sob condições de estresse hídrico, aumentando alguns parâmetros vegetais como, parte aérea e sistema radicular analisados.

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En este estudio se pretende caracterizar las comunidades vegetales presentes en ambientes litorales en el SE de la provincia de Alicante, mediante el cartografiado de zonas homogéneas de vegetación, mediante el empleo de los catálogos propuestos por el RAC-SPA y Medwet. De este modo, se han determinado 7 unidades ambientales en cada uno de los sectores analizados en el estudio (saladar de Urbanova y el Fondet de la Senieta), pudiendo comparar las diferencias entre ambas técnicas. Así, se seleccionaron 10 parcelas al azar y su vegetación fue muestreada según la metodología, basada en transectos, denominada «quadrat technique» y se identificaron las diferentes especies vegetales en el campo. Por otro lado, la medida de la cobertura vegetal total también fue tomada según la metodología de «Braun Blanquet». Se han empleado los programas informáticos CartaLinx® y ArcView® para el cartografiado de las unidades vegetales. Así, trabajo se pretende proporcionar herramientas técnicas y garantizar la gestión sostenible de los humedales y sus recursos naturales.

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The combined effects of drought stress and grazing pressure on shaping plant–plant interactions are still poorly understood, while this combination is common in arid ecosystems. In this study we assessed the relative effect of grazing pressure and slope aspect (drought stress) on vegetation cover and soil functioning in semi-arid Mediterranean grassland–shrublands in southeastern Spain. Moreover, we linked these two stress factors to plant co-occurrence patterns at species-pair and community levels, by performing C-score analyses. Vegetation cover and soil functioning decreased with higher grazing pressure and more south-facing (drier) slopes. At the community level, plants at south-facing slopes were negatively associated at no grazing but positively associated at low grazing pressure and randomly associated at high grazing pressure. At north-facing slopes, grazing did not result in a shift in the direction of the association. In contrast, analysis of pairwise species co-occurrence patterns showed that the dominant species Stipa tenacissima and Anthyllis cytisoides shifted from excluding each other to co-occurring with increasing grazing pressure at north-facing slopes. Our findings highlight that for improved understanding of plant interactions along stress gradients, interactions between species pairs and interactions at the community level should be assessed, as these may reveal contrasting results.

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Desalinated brackish groundwater is becoming a new source of water supply to comply with growing water demands, especially in (semi-) arid countries. Recent publications show that some chemical compounds may persist in an unaltered form after the desalination processes and that there is an associated risk of mixing waters with different salinity for irrigation. At the university of Alicante campus (Spain), a mix of desalinated brackish groundwater and water from the existing aquifer is currently applied for landscape irrigation. The presence of 209 emerging compounds, surfactants, priority substances according to the 2008/105/EC Directive, 11 heavy metals and microbiological organisms in blended water and aquifer samples was investigated. Thirty-five compounds were detected (pesticides, pharmaceuticals and surfactants) among them two priority substances α-endosulfan and Ni were found above the permitted maximum concentration. Blended water used for landscape irrigation during the summer period is supersaturated with respect to carbonates, which may ultimately lead to mineral precipitation in the soil-aquifer media and changes in hydraulic parameters.

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Irrigated agriculture is usually performed in semi-arid regions despite scarcity of water resources. Therefore, optimal irrigation management by monitoring the soil is essential, and assessing soil hydraulic properties and water flow dynamics is presented as a first measure. For this purpose, the control of volumetric water content, θ, and pressure head, h, is required. This study adopted two types of monitoring strategies in the same experimental plot to control θ and h in the vadose zone: i) non-automatic and more time-consuming; ii) automatic connected to a datalogger. Water flux was modelled with Hydrus-1D using the data collected from both acquisition strategies independently (3820 daily values for the automatic; less than 1000 for the non-automatic). Goodness-of-fit results reported a better adjustment in case of automatic sensors. Both model outputs adequately predicted the general trend of θ and h, but with slight differences in computed annual drainage (711 mm and 774 mm). Soil hydraulic properties were inversely estimated from both data acquisition systems. Major differences were obtained in the saturated volumetric water content, θs, and the n and α van Genuchten model shape parameters. Saturated hydraulic conductivity, Ks, shown lower variability with a coefficient of variation range from 0.13 to 0.24 for the soil layers defined. Soil hydraulic properties were better assessed through automatic data acquisition as data variability was lower and accuracy was higher.