Denise Cybis Fontana

Associação entre El Niño Oscilação Sul e a produtividade do milho no Estado do Rio Grande do Sul

The high interannual variability of corn yield in Rio Grande do Sul State is determined mostly by the variability of rainfall, which is mainly associated to El Nino Southern Oscillation (ENSO). Current availability of seasonal ENSO forecasts shows the possibility of using this information to minimize losses and maximize yield. However, it is necessary to assess the vulnerability of corn yield to this phenomenon. The objective of this work was to quantify the association between corn yield and rainfall variability due to ENSO. In order to perform the analysis, historical series of yields, monthly rainfalls, ENSO (El Nino and La Nina) phases, Sea Surface Temperature (SST) in equatorial Pacific, and the Southern Oscillation Index (SOI) were used. Results show that there is a strong trend for El Nino to favor corn crops, providing opportunities for high yields, while in years when La Nina occurs there is a high frequency of low yields. The rainfall most associated with corn yields is the integrated one from October to March. This information is useful for decision making as to crop management alternatives when there is a forecast of El Nino or La Nina.

Modelo de estimativa de rendimento de soja no Estado do Rio Grande do Sul

Este trabalho teve como objetivo parametrizar e validar o modelo multiplicativo de Jensen modificado para a estimativa do rendimento da cultura da soja no Estado do Rio Grande do Sul, em condicoes de lavoura. O ajuste foi feito usando dados meteorologicos de seis estacoes localizadas na regiao de producao significativa dessa cultura e dados de rendimento medio de todo o Estado, oriundos de estatisticas oficiais do IBGE, no periodo 1974/75 a 1994/95. O modelo apresentou bom ajuste, com coeficientes de determinacao de 0,86 para o modelo completo (novembro a abril) e 0,75 para o modelo reduzido (janeiro a marco). A validacao do modelo, feita com dados das safras 1995/96, 1996/97, 1997/98 e 1998/99, mostrou um bom desempenho, indicando que a agua e o fator isolado que maior influencia exerce na definicao do rendimento da soja no Rio Grande do Sul e, portanto, pode ser incorporado a programas de previsao de safras.

An agrometeorological-spectral model to estimate soybean yield, applied to southern Brazil

Soybean yield is modelled from data gathered from crops in Rio Grande do Sul State, Brazil. The model comprises an agrometeorological term, obtained by adjusting the multiplicative model of Jensen, modified by Berlato, and a spectral term, obtained from National Oceanic and Atmospheric Administration (NOAA) satellite images of the maximum Normalized Difference Vegetation Index (NDVI). The weather data used to calculate the relative evapotranspiration (ET r /ET 0) cover the period from 1975 to 2000, and the NDVI/NOAA images were obtained from 1982 to 2000. Application of the agrometeorological–spectral model produced better yield estimates (of about 5%) than Jensens model, allowing the further generation of yield maps for the most significant soybean production regions within the Rio Grande do Sul State.

Risco de deficiência hídrica decendial na metade sul do Estado do Rio Grande do Sul

Conduziu-se o presente estudo com o objetivo de se avaliar o risco de ocorrencia de deficiencia hidrica decendial da metade sul do estado do Rio Grande do Sul; para tanto, obtiveram-se dados diarios de temperatura maxima e minima, insolacao e precipitacao pluvial de nove localidades, distribuidas nas cinco regioes ecoclimaticas (Campanha, Depressao Central, Grandes Lagoas, Litoral e Serra do Sudeste) da metade sul do Estado, do periodo 1961-1990. Realizaram-se balancos hidricos decendiais seriados pelo metodo de Thornthwaite-Mather com capacidade de armazenamento de agua no solo de 50 e 125 mm. A partir dai, obteve-se o indice hidrico decendial (IH = ETR/ETo). Para analisar o risco de ocorrencia de deficiencia hidrica adotou-se o limite 0,6 como valor critico. Os resultados mostram que a regiao da Campanha e a de maior probabilidade de ocorrencia de deficiencia hidrica decendial, principalmente no periodo compreendido entre o 2o decendio de dezembro e o 2o de janeiro.

Avaliação de fluxos de calor e evapotranspiração pelo modelo SEBAL com uso de dados do sensor ASTER

The objective of this study was to evaluate the efficiency of SEBAL model in estimating soil surface energy fluxes and daily evapotranspiration for a large area of irrigated rice farms, near the municipality of Paraiso do Sul, RS, Brazil, using data from ASTER sensor. The evaluated variables are important weather and climatic parameters for agrometeorological studies and rationalization of water use. The conventional methodologies for estimating these parameters generally present uncertainties, which increase when concern is in the spatial behavior of such parameters. The Surface Energy Balance Algorithm for Land (SEBAL) was applied in an Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) scene and the estimates were compared to micrometeorological data retrieved from a station located in the studied area. The most accurate modeled parameter estimatives were sensitive heat and evapotranspiration, and the one which presented the highest error was soil heat flux. The adopted methodology was able to reproduce surface energy fluxes for agrometeorological and crop yield studies.

Identificação da dinâmica espaço-temporal para estimar área cultivada de soja a partir de imagens MODIS no Rio Grande do Sul

The objective of this study was to define a method for estimating soybean crop area in the Northern Rio Grande do Sul state (Brazil). Overall, six different remote sensing methods were proposed based on spectral-temporal profile and minimum and maximum values of NDVI/MODIS related to the stages of sowing, maximum development and harvesting of soybean areas. The resulting estimates were compared to official crop area data provided by the Brazilian government, using statistical analysis and the fuzzy similarity method. The performance of each method depended on information such as crop size, type of crop management, and sowing/harvesting dates. Regression coefficients of determination and fuzzy agreement values were above 0.8 and 0.45, respectively, for all methods. For operational monitoring of soybean crop area, the empirical threshold applied to the image difference with inclusion of harvest image method was the most effective, producing estimates that matched closely the official data. For spatial analysis the application of multitemporal images classification method is recommended that generated a map of better quality. The efficiency of these methods should be evaluated in the areas of soybean expansion in the state.

Modelo agrometeorológico-espectral de estimativa de rendimento de grãos de trigo no Rio Grande do Sul

Este trabalho teve como objetivo construir uma regressao linear multipla, empregando variaveis agrometeorologicas e espectrais, para estimativa de rendimento de graos de trigo, em municipios pertencentes a regiao de atuacao da Cooperativa Cotrijal (norte do Rio Grande do Sul). Para isso, foram empregados dados de rendimento (1991 a 2006), dados agrometeorologicos mensais (1991 a 2006) e dados espectrais (imagens NDVI/MODIS, 2000 a 2006). Foi analisada existencia de aumento significativo no rendimento de graos, decorrente da incorporacao de novas tecnologias (tendencia tecnologica). Para escolha das variaveis independentes da regressao linear, foi analisada a correlacao dos dados agrometeorologicos e espectrais com os dados de rendimento. Definidas as variaveis, foi construida uma regressao linear multipla de estimativa de rendimento de graos de trigo. Os resultados mostraram que nao houve aumento significativo no rendimento de graos de trigo da Cotrijal, no periodo analisado. Foram escolhidas as seguintes variaveis independentes para construcao da regressao linear multipla: precipitacao pluvial (outubro), indice de dano por geadas (setembro), graus-dia (acumulados de maio a outubro) e indice de vegetacao por diferenca normalizada (integrado de junho a outubro). As regressoes lineares multiplas apresentaram resultados satisfatorios, com erros de estimativa inferiores a 10%, na maior parte dos anos analisados. As caracteristicas de precisao, facil execucao e baixo custo das regressoes apontaram para possibilidade de uso conjunto de dados agrometeorologicos e espectrais, na estimativa de rendimento de graos de trigo. Mais estudos sao necessarios para verificacao dos resultados dos modelos, quando da incorporacao de uma serie mais longa de dados espectrais.

Indicadores de produção de soja no Rio Grande do Sul comparados ao zoneamento agrícola

The State of Rio Grande do Sul is responsible for approximately 20% of the national soybean production. For this reason better knowledge about pointers of this crop production in this State becomes necessary. The objective of this work was to analyse, comparing to the agricultural zoning, some soybean production pointers in the counties that are part of the signicant production region of this crop in Rio Grande do Sul. The grouping analysis was carried by the Wards method. Counties were grouped according to the yield, the production and the ratio of the soybean harvested area and the total county area. The yield grouping analysis result was compared to the soybean agroclimatic zoning for the State. There is narrow relation among the groups formed by the three variables analysis. The soybean agroclimatic zoning in the State of Rio Grande do Sul presents a possible inconsistency in the grouping of the counties by yield. In the other groupings, this inconsistency is not observed.

Desenvolvimento das culturas de cereais de inverno no Rio Grande do Sul por meio de perfis temporais do índice de vegetação por diferença normalizada

This research aimed to elaborate temporal NDVI profiles through the crop masks building, and find the interannual variations of profiles associated with variation of wheat grain yield in Rio Grande do Sul, Brazil. The data set were composed by MODIS13 images (NDVI product from May to November, 2000 to 2006), ground control points (collected in wheat, oat and barley fields) and official wheat grain yield (IBGE and Cotrijal). The results showed that using the proposed methodology for crop masking it is possible to generate consistent NDVI temporal profiles, which allows monitoring the development of winter cereal crops and can be used to evaluate the interannual variations of grain yield. The profiles showed that wheat grain yield was related to the maintenance of high NDVI values (above 0.7) for a larger period of time. However, the methodology did not allow the wheat, oats and barley discrimination, pointing for subsequent studies.

Série temporal de índice de vegetação sobre diferentes tipologias vegetais no Rio Grande do Sul

The objective of this study was the identification of the phenology dynamics of the main types of vegetation of Rio Grande do Sul state, for the period from 2000 to 2010, using Enhanced Vegetation Index data through the wavelet transform. The identification of cycles or seasonal patterns in time series of vegetation indices obtained by orbital sensors allows the observation of anomalies and effects of climate and environmental change. A temporal profile of Enhanced Vegetation Index was built for the Rio Grande do Sul region, where samples of the four main plant typologies were selected: native grassland, mixed ombrophilous forest, soybean and rice crop. These samples were submitted to the wavelet transform, which allowed the decomposition of the series and presentation of data in relation to time and frequency with which the phenological events have occurred. The data showed regularity in the dynamics of vegetation types tested, with annual cycles of plant growth and higher Enhanced Vegetation Index values in spring and summer and lower Enhanced Vegetation Index values in autumn and winter.