Hydrological approaches to measure or estimate crop water use – A theoretical background

Hydrological methods are used to retrieve actual evapotranspiration (ETa) as an alternative to micrometeorological techniques. This approach consists in performing the mass balance at a well-defined control volume. Despite the apparent theoretical simplicity of these methods, it is very common to witness their incorrect use, due to the lack of consistency in the definition of their terms by different authors, not only in measurements but also and mainly in common estimations for irrigation scheduling. Therefore, this article aims to review the main concepts and basic definitions of the hydrological methods, especially in the context of irrigation applications in climates with dry summer. The main topics addressed consist of: i) Mass balance and control volume; ii) Soil water thresholds for engineering applications; iii) Evapotranspiration or its components as output variables of water balance equation; iv) Applications of the water balance equation using actual evapotranspiration as input variable. This article is meant as a didactic text in the field of irrigation and drainage to support the learning of concepts related to the water balance. It also includes a set of application exercises to improve the comprehension of this subject.N/

Impacte das alterações climáticas nas necessidades de rega das culturas

Conhecidos os valores diários das variáveis meteorológicas evapotranspiração de referência (ETo) e precipitação (P) para a série de controlo e para as séries referentes aos vários cenários das alterações climáticas, pode-se estimar as necessidades de rega relativas a cada um dos cenários referidos através da simulação do balanço hídrico dos solos. Para o efeito, é ainda necessário conhecer os parâmetros hidrológicos dos solos e os parâmetros das culturas. Para a realização do balanço hídrico foi desenvolvido uma ferramenta informática que permite fazer o balanço hídrico sequencial de uma cultura ou de uma rotação de culturas

Production of Preserved Forage for Horses under Water Scarcity Conditions: A Case Study

The Mediterranean region is one of the areas most affected by climate change, which influences the production of forages. This has led producers to change from one to several forage cuttings, aiming to maintain crop productivity in increasingly water-scarce conditions. This study aimed to evaluate the nutrient content and productivity of forage produced for horses when subjected to variable water availability conditions at a Lusitano stud farm located in the central region of Portugal. The soil water content was evaluated throughout the growing season, using the gravimetric method, with soil samples collected every 15 days. Forage samples were collected from three grass cuttings (two for haylage and one for hay production), harvested from the same sward during the 2018/2019 growing season. The nutrient content of the forage samples was determined by chemical analysis. The global productivity throughout the crop-growing season was 8.3 t DM ha1, with the second harvest presenting the highest productivity (3.42 t DM ha1), corresponding to an adequate water supply, whereas the last cut, produced under water deficit conditions, presented the lowest productivity (2.1 t DM ha1). The estimated nutritive value by chemical composition analysis for both haylage and hay fell within the range reported in the literature for preserved forages for horsesinfo:eu-repo/semantics/publishedVersio

Climate change impacts for irrigation requirements of preserved forage for horses under Mediterranean conditions

Pasture and forage production occupies a large part of the utilized agricultural area in Portugal, a country prone to the e ects of climate change. This study aims at evaluating the impacts of climate change on forage irrigation requirements and at defining and assessing di erent adaptation measures. A second objective focuses on evaluating the impacts on water deficit of rainfed forages. This study was performed in a Lusitano horse stud farm located in Azambuja Municipality, Portugal. The climate change impacts on the crop irrigation requirements and crop water deficit were simulated using the soil water balance model, ISAREG. The reference period considered was 1971–2000 and the climate scenarios were the Representative Concentration Pathways (RCPs) 4.5 and 8.5 (2071–2100). The results show that the adaptation measure aiming at maximum production (several cuts) will increase the irrigation requirements in the di erent climate change scenarios between 38.4% and 67.1%. The adaptation measure aiming at reducing the water consumption (only one cut) will lead to a reduction in irrigation requirements in the di erent climate change scenarios, ranging between 31.1% and 64.0%. In rainfed conditions, the water deficit is substantially aggravated in the climate change scenariosinfo:eu-repo/semantics/publishedVersio

Milk production as an indicator of drought vulnerability of cities located in the brazilian semiarid region

Several spectral indices have been used to estimate droughts, however, these indicators only give evidence of a dry spell leaving out its impacts on significant economic activities performed in a given region. In this context, livestock breeding in one of the most important activities to analyze in the Brazilian semiarid region. The aim of this study was to evaluate the relationship between the drought indices, obtained through remote sensory devices, and annual milk production (2004 – 2014), identifying the most affected cities by the drought and were considered the most vulnerable and in need of special attention during dry periods. In order to analyze the data, the hierarchical grouping technique and correlation analyses between milk production and VCI - Vegetation Condition Index, TCI - Temperature Condition Index, VHI - Vegetation Health Index, PCI - Precipitation Condition Index and SDCI - Scaled Drought Condition indices were used. The intense correlation between milk production and the drought indices may be related to the dependency of the cities’ economies on natural resources. On the other hand, the diversification of the cities’ economic activities may enable access to various resources and drought vulnerability reductioninfo:eu-repo/semantics/publishedVersio

Estudo comparativo das alterações climáticas e da sua influência sobre as necessidades de rega no clima Mediterrâneo

É geralmente aceite que o aumento das emissões de gases com efeito de estufa, e a utilização extensiva de combustíveis fósseis está a provocar uma alteração climática ao nível mundial. O crescimento das culturas é muito afectado pelo clima e as suas alterações podem afectar seriamente a segurança alimentar a nível global. Por outro lado, as reservas de água para a rega estão a diminuir e é importante avaliar os efeitos das alterações climáticas sobre o consumo de água pelas plantas. Estudos anteriores indicam que na Ibéria as temperaturas médias do ar aumentaram ao ritmo de 0,3-0,7 ºC década-1 em Espanha e 0,4 ºC década-1 no Sul de Portugal. O presente estudo utiliza séries de dados de 20 anos da Califórnia, região que também tem um clima Mediterrâneo, para estudar as implicações das alterações climáticas sobre as necessidades de rega. Os dados referem-se a 20 estações climáticas distribuídas pelo Estado da Califórnia. Os resultados indicam que as temperaturas aumentaram ao ritmo de 0,15 ºC década-1 nos últimos 20 anos, o que está de acordo com a tendência de aumento da temperatura do ar verificada em estudos realizados em Portugal e Espanha. Adicionalmente, a radiação solar aumentou em 8 W m-2 durante os vinte anos do estudo, o que representa um aumento de 4% na energia total recebida através da radiação. Este aumento no input de energia solar, associado ao aumento da temperatura resultou num aumento de 0,11 mm dia-1 década-1 na evapotranspiração calculada pelo método de CIMIS Penman e de 0,12 mm dia-1 década-1 na evapotranspiração quando calculado pela equação de Penman Monteith. Estes valores representam um aumento de, respectivamente, 6,6 e 7,2% no período 1991-2011

Climate change adaptation measures in the irrigation of a super-intensive olive orchard in the south of Portugal

The south of Portugal is one of the regions that will be most affected by the impacts of climate change (CC), with an expected increase in water scarcity. Irrigated super-intensive olive orchards occupy a large area of the used agricultural surface in the Alentejo region, south of Portugal, making it necessary to adapt this crop to the effects of CC. This study assessed the impacts of CC and defined adaptation measures concerning irrigation management of the super-intensive olive orchard. To compute the crop irrigation requirement (CIR), the soil water balance model ISAREG was combined with climate data relative to the reference period 1971–2000 and to the representative concentration pathways RCP4.5 and RCP8.5 for the periods 2011–2040, 2041–2070, and 2071–2100. The growing degree-days (GDD) approach was used to estimate olive phenology for these CC scenarios. Unchanged irrigation management with an average CIR increase up to 16% in RCP4.5 and 31% in RCP8.5 is expected. By adopting higher levels of water deficit, water savings of up to 22% can be realized. The results showed that the anticipated CIR increase for the CC scenarios can be mitigated through regulated deficit irrigation strategiesinfo:eu-repo/semantics/publishedVersio

ESTUDO DE ALGUNS IMPACTOS DAS ALTERAÇÕES CLIMÁTICAS SOBRE O REGADIO NO ALENTEJO

A actividade humana, associada a uma utilização desmedida de combustíveis fósseis, tem produzido efeitos negativos sobre a fauna, a flora e o ciclo hidrológico. Para avaliar os efeitos sobre o ciclo hidrológico na região do Alentejo, foram estudados os registos meteorológicos disponíveis na base de dados do INAG de todas as estações da região. O estudo baseou-se em médias mensais e anuais de precipitação, temperatura, radiação, vento e evapotranspiração calculada pelos métodos de Penman-Monteith ou Hargreaves. A variabilidade dos dados foi atenuada utilizando médias móveis com diferentes durações. Os resultados mostram um aumento gradual das temperaturas médias da região, que em algumas zonas atinge um ritmo de 0,4ºC por década. Por outro lado, também se verificam alterações sazonais sobre os restantes parâmetros climáticos, com importância para a evapotranspiração e consumos hídricos das culturas. Human activity, associated with an unprecedented use of fossil fuels has had a negative effect on the plants, animals and the hydrological cycle. In order to assess the effect of these changes on the hydrological cycle in the Alentejo region, meteorological records available at INAG were studied. The study was based on the monthly and annual averages of rainfall, temperature, radiation, wind speed, and evapotranspiration calculated by the Penman-Monteith and Hargreaves methods. The variability of the data was attenuated using moving averages with different lengths. The results demonstrate a gradual increase of the average temperatures of the region, where some areas show a decanal increase of 0,4ºC. On the other hand, there are also seasonal changes in the remaining climate parameters, that are important for evapotranspiration and crop water consumption

Framework for assessing collective irrigation systems resilience to climate change—The Maiorga case study

In order to increase water productivity at the Collective Irrigation System (CIS) level it is crucial to adapt the existing irrigation infrastructure, enhancing water intake at the source, as well as its transport and delivery efficiency. Rehabilitation may involve structural changes and thus, a large capital investment. This investment should be proportionate to the increase in climate resilience associated to different rehabilitation alternatives. A methodology framework was developed to evaluate CIS resilience to climate change considering different rehabilitation alternatives. The assessed components were: (i) crop production systems; (ii) on-farm irrigation systems; and (iii) project rehabilitation alternatives for the conveyance and distribution of the irrigation water from the source to the farmer fields. This framework was applied to the Maiorga CIS, in central Portugal, to test the methodology performance in assessing the impacts of climate change on the supply-demand balance of the proposed rehabilitation alternatives and to evaluate their climate resilience, for the representative concentration pathways, RCP4.5 and RCP8.5, and two time periods, 2041–2070 and 2071–2100. For each scenario, period, and rehabilitation alternative, irrigation requirements at the source (demand) and stream flows (supply) were computed and the supply-demand balance was performed. Projected increases in irrigation water demand varied between 5.5% for RCP4.5/2071–2100 and 35.7% for RCP8.5/2071–2100. For RCP4.5, 11% (2050) and 9% (2080) reductions in irrigation water supply were projected, while for RCP8.5 the reduction ranges between 13% (2050) and 30% (2080). The proposed framework determined that the rehabilitation alternatives considering just one type of water source, without flow regularization and with open channel distribution to the farmer’s field, have proved to be unviable due to low resilience to climate change.info:eu-repo/semantics/publishedVersio