Léo Fernandes Ávila

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.

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.

PARTIÇÃO DA PRECIPITAÇÃO PLUVIAL EM UMA MICROBACIA HIDROGRÁFICA OCUPADA POR MATA ATLÂNTICA NA SERRA DA MANTIQUEIRA, MG

The analyze of pluvial precipitation and its interaction on the different hydrologic cycle phases in forested watersheds are essential in order to water balance characterization due to its relevant participation in the hydrological processes and to its spatial-temporal variability as function of edaphic, topographic, climatic and vegetation elements. Due to heterogeneity of Atlantic Forest associated to temporal and spatial variability of pluvial precipitation regime, the study of mechanisms that allow describing and linking the hydrological cycle elements are very important. This way, the objective of this study was to analyze the partitioning of pluvial precipitation at a micro-catchment entirely occupied by Atlantic Forest remnant, in Mantiqueira Range, during 2009/2010 and 2010/2011 hydrological years, relating it with the seasonal evolution of this ecosystem which was monitored by the application of normalized difference vegetation indexes (NDVI). It was observed greater percentage of internal pluvial precipitation during the periods with less rainfall. It was also verified greater water storage capacity of the Atlantic Forests canopy throughout rainy season. Yet, a plausible correlation was obtained between water storage capacity of Atlantic Forest and the regeneration of vegetation demonstrated by NDVI what can be associated to the processes responsible for Atlantic Forests growth.

Spatial distribution of top soil water content in an experimental catchment of Southeast Brazil

Soil water content is essential to understand the hydrological cycle. It controls the surface runoff generation, water infiltration, soil evaporation and plant transpiration. This work aims to analyze the spatial distribution of top soil water content and to characterize the spatial mean and standard deviation of top soil water content over time in an experimental catchment located in the Mantiqueira Range region, state of Minas Gerais, Brazil. Measurements of top soil water content were carried out every 15 days, between May/2007 and May/2008. Using time-domain reflectometry (TDR) equipment, 69 points were sampled in the top 0.2 m of the soil profile. Geostatistical procedures were applied in all steps of the study. First, the spatial continuity was evaluated, and the experimental semi-variogram was modeled. For the development of top soil water content maps over time a co-kriging procedure was used having the slope as a secondary variable. Rainfall regime controlled the top soil water content during the wet season. Land use was also another fundamental local factor. The spatial standard deviation had low values under dry conditions, and high values under wet conditions. Thus, more variability occurs under wet conditions.

Padrão espaço-temporal da umidade volumétrica do solo em uma bacia hidrográfica com predominância de latossolos

A umidade volumetrica do solo possui alta variabilidade espacial e temporal devido a influencia de varios fatores ambientais e de uso do solo. Desse modo, seu entendimento assume papel fundamental na modelagem dos processos que envolvem o escoamento superficial, a erosao do solo e o transporte de sedimentos. Nesse contexto, objetivou-se neste estudo avaliar o padrao espacial e temporal da umidade volumetrica na camada superficial do solo, nas diferentes estacoes do ano, em uma bacia hidrografica experimental, com predominância de latossolos, localizada na regiao Sul de Minas Gerais. Para isso, utilizou-se o conceito de estabilidade temporal e escalonamento de semivariogramas, o qual possibilitou a comparacao da estrutura espacial dos modelos de semivariogramas ajustados. Foi possivel detectar forte dependencia espacial da umidade do solo na bacia hidrografica, com grau de dependencia sempre acima de 80 %, e os semivariogramas escalonados mostraram semelhancas no padrao espacial no verao e no outono e diferencas em relacao ao inverno e a primavera. Dessa forma, constatou-se que houve diferenca no padrao espacial da umidade do solo ao longo do ano, contudo maior homogeneidade no periodo chuvoso (verao). Ocorreu variacao no padrao temporal de umidade do solo de acordo com as estacoes do ano, sendo verificada tendencia nos dados de inverno e primavera, demonstrada pelo teste de Spearman. Devido as diferencas verificadas no padrao espacotemporal da umidade do solo ao longo das estacoes do ano, quatro pontos distintos foram identificados, um em cada estacao, para implantacao de monitoramento permanente desse atributo do solo na bacia hidrografica.

Spatial continuity and distribution of soil moisture in a watershed of the Mantiqueira Range

The knowledge related to the spatial continuity of the soil moisture is essential for understanding and prediction of the hydrological processes. The geostatistical methodology has often been applied in such studies. In this context, the semi-variogram is used to model the spatial continuity of a specific variable for its mapping. This work aimed to model the spatial continuity of soil moisture in an experimental watershed located in Mantiqueira Range, MG, and then to generate map of soil moisture through the year. Exponential, spherical and gaussian semi-variogram models were fitted applying the Ordinary Least Square, Weighted Minimum Square and Maximum Likelihood methodologies, testing their adherence based on the Spatial Dependence Degree and database from Cross-Validation procedure. The exponential model presented better performance in 59% of the situations. The mean Spatial Dependence Degree was 88%, showing a strong dependence degree to the spatial continuity structure. The soil moisture mapping demonstrated behavior strongly associated to the land use and topographical conditions.

Spatial continuity of soil attributes in an Atlantic Forest remnant in the Mantiqueira Range, MG

The spatial characterization of soil attributes is fundamental for the understanding of forest ecosystems. The objective of this work was to develop a geostatistical study of chemical and physical soil attributes at three depths (D1 - 0-20 cm; D2 - 20-50 cm; D3 - 50-100 cm), in an Experimental Hydrographic Micro-catchment entirely covered by Atlantic Forest, in the Mantiqueira Range region, Minas Gerais. All the considered variables presented spatial dependence structure in the three depths, and the largest degrees of spatial dependence were observed for pH in the three depths, soil cation exchange capacity potential in D3, soil organic matter in D1 and D3 and clay and soil bulk density in D2. The method most used for the adjustments of semi-variogram models was the Maximum Likelihood and the most selected model was the Exponential. Furthermore, the ordinary kriging maps allowed good visualization of the spatial distribution of the variables.

Water quality indicators in the Mantiqueira Range region, Minas Gerais state

Maintaining the quality of water resources is of great importance for environmental preservation and the quality of life of consumers, and is one of the greatest challenges facing humanity today. Land-use for agriculture and animal farming significantly changes the biological, physical and chemical characteristics of natural systems. This study comprised monitoring of two subbasins located in the Mantiqueira Range region, from which water samples were collected on a monthly basis between June 2010 and May 2011 for analysis. Each subbasin has a distinct vegetation cover, one being predominantly covered by pastureland and the other being entirely covered by Atlantic Forest. The following water quality indicators were analyzed: turbidity, pH, electrical conductivity, total dissolved solids, dissolved oxygen, temperature, nitrate, phosphate, BOD,COD, total and fecal coliforms, and respective discharge measurement. The results showed that water quality degradation in both environments coincided with the local rainy season and was influenced by transport of organic material to watercourses by direct surface runoff. The high concentrations of fecal coliforms found affected the water quality, particularly in the rainy season, and are associated with agriculture and animal farming, the main economic activities in the region. The Atlantic Forest environment, however, had statistically better water quality over time in relation to the pastureland environment, due to the buffering it provides to direct surface runoff.

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.

Tendências de temperaturas mínimas e máximas do ar no Estado de Minas Gerais

The objective of this work was to evaluate the trends in minimum and maximum air temperatures in the state of Minas Gerais, Brazil. Data from 43 municipalities were analyzed, considering annual and seasonal scales - January, April, July, and October, which represent the middle months of summer, autumn, winter, and spring, respectively. Historical series of minimum and maximum daily air temperatures, from at least 30 year, were analyzed by the Mann-Kendall test and linear regressions. Trends were considered significant only if both evaluations were significant; in this case, the rates of temperature shift were determined. There was good agreement between the statistical tests for detecting trends in the historical series, for most municipalities. An increasing temperature trend of up to 1.5 o C per decade was observed for minimum temperatures in July, with generalized increasing trends in the greatest part of the state in January and October, and also in the annual scale. Exceptions were verified mainly in municipalities at higher altitudes, in which minimum air temperatures decreased in winter. There is a predominance of municipalities with significant increasing temperature trend, regardless of the evaluation scale. Increasing temperature trends are expected to be more common in the south to north direction, in the state of Minas Gerais.