Marcelo Ribeiro Viola

Métodos de interpolação espacial para o mapeamento da precipitação pluvial

A espacializacao de variaveis climaticas, notadamente a precipitacao pluvial, necessita de estudos constantes, visando ao aperfeicoamento de interpoladores e desenvolvimento de mapas sem tendencia. Objetivou-se, neste contexto, avaliar o desempenho dos interpoladores krigagem (KG), a partir do melhor modelo de semivariograma, cokrigagem (CA), introduzindo a altitude como variavel secundaria, modelagem estatistica (ME), na qual a precipitacao media pode ser estimada a partir de coordenadas geograficas, e inverso do quadrado da distância (IQD), para espacializacao da precipitacao media mensal, precipitacao media do periodo seco e precipitacao media anual, em Minas Gerais; para isto se utilizaram informacoes de 232 postos pluviometricos para modelagem e de 70 para validacao, com base no erro medio absoluto, alem de um modelo digital de elevacao com resolucao de 270 m. Quanto a avaliacao dos metodos de interpolacao, constatou-se bom desempenho das metodologias abordadas, com erro absoluto medio variando de 12,84 a 19,96%, com destaque para a cokrigagem, que obteve menor erro em 50% das situacoes analisadas.

Hydrologic modeling in the Aiuruoca river basin, Minas Gerais State.

A simulacao do comportamento hidrologico de bacias hidrograficas consiste em uma das principais ferramentas na gestao dos recursos hidricos, devido a possibilidade de predicao do regime fluvial. A bacia em estudo esta localizada na regiao Alto Rio Grande, Sul de Minas Gerais, com area de drenagem de 2.094 km², constituindo uma das bacias fundamentais de drenagem para o reservatorio da Usina Hidreletrica de Camargos (UHE - Camargos/CEMIG). Neste contexto se objetivou desenvolver e aplicar um modelo hidrologico semi-conceitual, na forma semi-distribuida, para simular o comportamento hidrologico da bacia do Rio Aiuruoca, com apoio dos SIGs e sensoriamento remoto, disponibilizando uma ferramenta util para o gerenciamento e planejamento dos recursos hidricos na regiao. Os resultados do coeficiente estatistico de Nash-Sutcliffe (CNS) foram de 0,87 e 0,92 para as etapas de calibracao e verificacao, respectivamente, o que, de acordo com a classificacao proposta para modelos hidrologicos de simulacao, permite qualifica-lo para simulacao do comportamento hidrologico na bacia hidrografica do Rio Aiuruoca.

Variabilidade espacial de atributos físicos do solo associados ao uso e ocupação da paisagem

This work aimed to diagnose current agricultural soil use as well as its implications for the spatial variability of soil bulk density (Ds), organic matter (OM), particle-size distribution and water dispersible clay (WDC), in Ribeirao Marcela watershed, belonging to Alto Rio Grande region, using geostatistics tools, in order to observe occurrence patterns of these attributes in the landscape. Disturbed and undisturbed soil samples were collected in 0-0.15 m layer, in a grid of 240 x 240 m (macro-scale) and 60 x 60 m (micro-scale), resulting in 165 samples. Current soil use is not in accordance to soil class agricultural suitability. Soil bulk density presented values between 1.05 and 1.15 g cm-3, this range being above characteristic values for Oxisol (close to 0.95 g cm-3), with the highest values found in lands under pasture. Organic matter values ranges from 1.5 to 4.5 dag kg-1, detecting higher concentrations in lands under eucalyptus, cerrado and wetlands. Particle-size distribution presented behavior following the drainage pathways and WDC presented low values in the entire watershed. Kriging maps were shown to be important tools for the understanding of spatial variability of physical soil attributes in the watershed, indicating critical management areas.

Applicability of the LASH Model for Hydrological Simulation of the Grande River Basin, Brazil

AbstractThe Lavras Simulation of Hydrology (LASH) hydrological model is classified as a deterministic, semiconceptual, and spatially distributed model. This model was developed to make available a tool for hydrological analysis in watersheds with a limited database, and it has presented good streamflow predictions. The aim of this study was to calibrate and validate the LASH model for hydrological simulation of the following watersheds which make up the headwaters of the Grande River basin (southern Minas Gerais state, Brazil): the Aiuruoca, Grande, Sapucai, and Verde river basins. The LASH model simulated adequately the hydrological regimes of the previously mentioned watersheds, presenting satisfactory performances for all the watersheds, which can be emphasized by the Nash-Sutclifffe coefficient (CNS) values greater than 0.70. The analysis of the main hydrological processes simulated by the LASH model confirmed that the results were consistent with the hydrological characteristics observed on the respe...

Probable minimum precipitation mapping for the Southern Minas Gerais, Brazil

The probable minimum precipitation associated to the period, location and frequency of occurrence represents an important tool to support agricultural practices. The objective of this work was to map the probable minimum monthly and fortnightly precipitation for Southern Minas Gerais State, applying geostatistical procedures. The probability level considered was 75% and the period evaluated was the rainy season. The values of probable minimum precipitation were estimated by Log-Normal Probability Distribution, following Kolmogorov-Smirnov adequacy test and using long-term daily precipitation data set of 69 pluviometric stations in the region and its surroundings. Exponential and spherical semi-variogram models, adjusted by Maximum Likelihood (ML) and Minimum Weighted Square (MWS), were modelled to choose the best to represent the experimental semi-variogram. Based on Spatial Dependence Degree and Cross-Validation, the exponential model adjusted by MWS presented better performance. The probable minimum precipitation maps have shown considerable variability during the rainy season. The greatest values were estimated for the region close to Mantiqueira and Canastra Ranges.

Estimativa do escoamento superficial em uma bacia hidrográfica com base em modelagem dinâmica e distribuída

Knowledge on the surface runoff in watersheds is very important for a good conservation of natural resources. However, surface runoff is a complex and dynamic process, especially in the context of spatial variability. An application of the Geographical Information System (GIS) tools in small grid cells is therefore adequate. This way, it is possible to consider the spatial behavior of variables associated to the origin of surface runoff. This study aimed to program the Hydrological Models SCS-CN (SCS-Curve Number) and CN - MMS (CN - Modified) based on the PC Raster Programming Language and a reduced dataset, in distributed and dynamic approaches, to estimate the direct surface runoff in a watershed of Oxissols, in the county of Nazareno, region of Campos das Vertentes, Minas Gerais State. SCS-CN model was applied structuring a CN-map linked to the soil infiltration capacity in the PCRaster GIS format. For the CN - MMS model, we used other maps: saturated volumetric soil moisture content, initial volumetric soil moisture content and soil depth. For the simulation and evaluation of both models, 18 rainfall events that produced surface runoff in the hydrologic year 2004-2005 were used, and their respective surface runoff depths observed. The model performance was evaluated by sensitivity analyses, based on the mean error and Root Square Error. Based on these accuracy statistics, the calibration of the CN - MMS model was better than in the original SCS-CN model, since the initial soil moisture was taken into account. Nevertheless, the adjustment of the models in the SIG PCRaster allowed the development of an effective and useful computer tool to simulate surface runoff, due to the possibility of establishing computer routines considering the problems elated to the spatial variability of data entries of the model.

Mapeamento de chuvas intensas no estado de Minas Gerais

Studies of heavy rainfall are of practical interest for the conservation management of natural resources such as watersheds and soil and water. The spatial distribution of these natural rainfall events allows conclusions about regions where the occurrence of heavy rain is more frequent and to estimate their magnitude for locations without rainfall data sets. Thus, the purpose of this study was to map heavy rainfall data from 177 meteorological stations, using a geostatistical approach, for Minas Gerais, identifying the most vulnerable regions in terms of the occurrence of heavy rain. The highest values were estimated for the East and Northwest regions of the state, which can be explained by the influence of the South Atlantic Converge Zone (SACZ), aside from convective rainfall events. In addition, the lowest and intermediate values were found and mapped, respectively, for the North/Northeast and Mid/South regions of the state. For the rainfall events with longest duration, intensities were high in the Southern region, which can be explained by the more frequent cold weather fronts that induce long-lasting rains.

Continuidade espacial da condutividade hidráulica saturada do solo na bacia hidrográfica do Alto Rio Grande, MG

Spatial distribution of the saturated hydraulic conductivity (k0) is essential in the study of soil erosion and surface runoff. The purpose of this study was to investigate the spatial continuity of the soil hydrologic characteristic k0 in the watershed Alto Rio Grande, state of Minas Gerais, and to map k0 based on geostatistical procedures, using data without and with logarithmic transformation. Exponential and spherical semi-variogram models were fitted to the experimental semi-variograms in two approaches: ordinary minimum square (MQO) and weighted minimum square (MQP). Cross validation and predictive validation were both applied to choose the best model. The results showed that the use of log (k0) improved the geostatistical applicability due to a reduction in the number of outliers and anisotropy; however, the spatial dependency degree was highest for k0 data without log-transformation. The spherical model fitted by MQO preformed best in the spatial continuity modeling of k0. The spatial distribution in the basin, indicated by the maps developed from data without and with log transformation was not the same; the map developed on the basis of log-transformed data showed a more detailed spatial distribution.

Distribuição espacial de valores prováveis de precipitação pluvial para períodos quinzenais, em Guiné-Bissau

The aim of this study was to estimate the probable values of rainfall in the first and second halves of the months and its spatial distribution in Guinea-Bissau. Distribution functions Log-normal 2 parameters were used to estimate the probable values of rainfall adopting the probability level of 75%. The spatial interpolation (kriging) was applied by semi-variogram modeling demonstrating that the probable rainfall estimates have high spatial variability, except in the month of September, when the behavior is homogeneous for both first and second halves. The lowest probable values of rainfalls under 50 mm occur in June and October throughout the country, supporting the use of supplemental irrigation to avoid compromising the periods of sowing (June) and minimize damage at harvest (October, November) for long cycle crops.

Distribuição e potencial erosivo das chuvas no Estado do Tocantins

O objetivo deste trabalho foi determinar os valores de erosividade e gerar os mapas da distribuicao espaco-temporal das chuvas no Estado do Tocantins. Analisaram-se series historicas pluviometricas de 97 postos pluviometricos, compreendendo o periodo de 1985 a 2009. A erosividade foi estimada por meio de equacoes nas quais a variavel independente foi a precipitacao media mensal ou o coeficiente de chuva de Fournier (Rc). A geoestatistica foi aplicada para o mapeamento da erosividade tanto na escala mensal quanto na anual. A erosividade anual apresentou valores entre 6.599 e 14.000 MJ mm ha-1 h-1, com auge em dezembro, quando atingiu valores de ate 2.800 MJ mm ha-1 h-1 por mes. De maio a setembro, a erosividade apresentou valores inferiores ao critico, tido como 500 MJ mm ha-1 h-1 por mes. Foram identificadas tres regioes prioritarias para acoes de planejamento visando a conservacao do solo e da agua: regiao centro-oeste do Estado, nas imediacoes do Parque Estadual do Cantao, com maior erosividade anual; regiao norte do Estado, especialmente no primeiro trimestre; e regiao sudeste do Estado, no quarto trimestre.