Lineu Neiva Rodrigues

Valores de tensão na determinação da curva de retenção de água de solos do Cerrado

A curva de retencao de agua do solo e essencial para o estudo das relacoes solo-agua. A escolha do numero e da combinacao de pontos a serem levantados para o seu tracado normalmente e feita de forma arbitraria. O objetivo deste trabalho foi definir o menor numero e a melhor combinacao de pontos de tensao que resultem na descricao da curva de retencao de agua de solos do Cerrado. Utilizaram-se cinco curvas de retencao de diferentes solos como referencia, cada uma com 15 pontos medidos pelo metodo da centrifuga e ajustada ao modelo de Genuchten. A partir desses 15 pontos, 385 curvas foram geradas para cada solo, com seis, sete, oito e nove pontos, a fim de serem comparadas com a curva de referencia. A analise da distribuicao estatistica da soma de quadrados dos erros padronizados, entre as curvas geradas e as respectivas curvas de referencia, permitiu definir um modelo de probabilidade que serviu como instrumento para a escolha das melhores combinacoes de pontos de tensao. A combinacao definida pelos oito valores de tensao de 1, 3, 6, 10, 35, 84, 611 e 1.515 kPa e a recomendada para o levantamento das curvas de retencao de agua de solos do Cerrado.

Economic impacts of regional water scarcity in the Sao Francisco River Basin, Brazil: an application of a linked hydro-economic model

This paper presents a linked hydro-economic model and uses it to examine the regional effects of water use regulations and product price changes on the agriculture of the Sao Francisco River Basin, Brazil. The effects of weather on surface water availability are explicitly addressed using the hydrological model MIKE-Basin. Farmers’ adjustments to changes in precipitation, surface water availability, and other factors are quantified using an economic model based on non-linear programming techniques. The models are externally linked. Results show that regional impacts, at the sub-basin level, vary depending on the location of each sub-basin relative to river flows. The effects of water use regulations and of exogenous price shocks on agriculture depend on weather, location, product mix and production technology. Implications of these results for policies designed to manage agriculture and water use are discussed.

Comparação de modelos matemáticos para o traçado de curvas granulométricas

A distribuicao granulometrica de particulas solidas e essencial para as areas de material de construcao, mecânica dos solos, fisica dos solos, hidrossedimentologia, entre outras. As tecnicas utilizadas na avaliacao da distribuicao granulometrica de amostras resultam em valores pontuais, dependendo de posterior interpolacao para o tracado da curva granulometrica e a obtencao de diâmetros caracteristicos especificos. A transformacao de valores pontuais em funcoes continuas pode ser realizada por meio de modelos matematicos. Entretanto, ha poucos estudos com a finalidade de determinar o melhor modelo para o ajuste de curvas granulometricas. O objetivo deste trabalho foi testar e comparar 14 diferentes modelos passiveis de utilizacao no tracado da curva granulometrica de particulas solidas com base em quatro pontos medidos. O parâmetro de comparacao entre os modelos foi a soma de quadrado dos erros entre os valores medidos e calculados. Os modelos mais recomendados no tracado da curva granulometrica, a partir de quatro pontos, sao os de Skaggs et al. 3P, Lima & Silva 3P, Weibull 3P e Morgan et al. 3P, todos com tres parâmetros de ajuste.

Proposição de um modelo matemático para a avaliação do desempenho de sistemas de irrigação

Mathematical models have been proposed to represent the applied irrigation water distribution profile, which is fundamental to evaluate the performance of irrigation systems. Even though there have been advances, so far, there is not a universally accepted model as the most adequate to fit water distribution profiles from irrigation systems. The objectives of this work were to propose a model for evaluating the performance of irrigation systems, and to develop an irrigation adjusting factor for calculating the gross water depth that takes into account both water application uniformity and efficiency measures. The fitting parameters of the proposed model were determined by using the routine Solver from the spreadsheet Excel and the water application uniformity and efficiency measures were calculated from mathematical expressions derived for this model. According to data from the evaluation of a center pivot irrigation system, the proposed model is adequate for analyzing irrigation performance and for obtaining the devised irrigation adjusting factor, by gathering the required system performance indicators. It also simplifies the analysis procedures and allows a direct calculation of the water depth demand for irrigation.

Assessing agriculture–water links at the basin scale: hydrologic and economic models of the São Francisco River Basin, Brazil

This article uses a basin-wide hydrologic model to assess the hydrologic and economic effects of expanding agriculture in the São Francisco River Basin, Brazil. It then uses a basin-wide economic model of agriculture to examine the effects of implementing water use regulations. Preliminary results suggest that substantially expanding agriculture would put pressure on some of the rivers environmental flows. Agricultural output and rural employment would increase, though not in spatially uniform ways. The economic model demonstrates how cropping area, crop mix and production technology respond simultaneously to water shortages. While farmers can adjust, the costs of doing so may be beyond the reach of resource-poor farmers.

Spatial patterns of rural poverty: an exploratory analysis in the São Francisco River Basin, Brazil

This paper uses recently released municipio-level data on rural poverty in Brazil to identify and analyze spatial patterns of rural poverty in the Sao Francisco River Basin (SFRB). Moran’s I statistics are generated and used to test for spatial autocorrelation, and to prepare cluster maps that locate rural poverty “hot spots” and “cold spots.” Our results indicate that poverty reduction policies in the SFRB should take into account the spatial distribution of poverty. Not only is poverty in the SFRB clustered spatially, but the bulk of the basin’s poor resides in municipios that comprise the poverty ‘hot spots’ we identified. These clusters did not correspond to state-level boundaries (the political delineations often used to measure poverty and to manage poverty reduction programs), so scope may exist for geographically refocusing poverty reduction efforts to make them more efficient. Maybe more importantly the results set the stage for the use of spatial econometrics for a future multivariate analysis of rural poverty in the basin.

Truncated location-scale non linear regression models

ABSTRACT We present a class of truncated non linear regression models for location and scale where the truncated nature of the data is incorporated into the statistical model by assuming that the response variable follows a truncated distribution. The location parameter of the response variable is assumed to be modeled by a continuous non linear function of covariates and unknown parameters. In addition, the proposed model also allows for the scale parameter of the responses to be characterized by a continuous function of the covariates and unknown parameters. Three particular cases of the proposed models are presented by considering the response variable to follow a truncated normal, truncated skew normal, and truncated beta distribution. These truncated non linear regression models are constructed assuming fixed known truncation limits and model parameters are estimated by direct maximization of the log-likelihood using a non linear optimization algorithm. Standardized residuals and diagnostic metrics based on the cases deletion are considered to verify the adequacy of the model and to detect outliers and influential observations. Results based on simulated data are presented to assess the frequentist properties of estimates, and a real data set on soil-water retention from the Buriti Vermelho River Basin database is analyzed using the proposed methodology.

Evaluation of hydrocyclone as pre-filter in irrigation system

The objective of this work was to evaluate the efficiency of a hydrocyclone to separate sand in irrigation water. To do this, it an experiment was conducted where the hydrocyclone was operated with pressures and discharge that varied from 10 to 60 kPa and from 1,159.90 L h-1 to 2,603.60 L h-1, respectively. During the tests, the sand concentration in suspension varied from 2.81 g L-1 to 7.01 g L-1. The results showed that the best efficiency was obtained with pressure differentials of 10 and 30 kPa, with cut size (d70) of 50 µm.