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We use models to simulate the real world mainly for prediction purposes. However, since any model is a simplification of reality, there remains a great deal of uncertainty even after the calibration of model parameters. The model’s identifiability of realistic model parameters becomes questionable when the watershed of interest is small, and its time of concentration is shorter than the computational time step of the model. To improve the discovery of more reliable and more realistic sets of model parameters instead of mathematical solutions, a new algorithm is needed. This algorithm should be able to identify mathematically inferior but more robust solutions as well as to take samples uniformly from high-dimensional search spaces for the purpose of uncertainty analysis. Various watershed configurations were considered to test the Soil and Water Assessment Tool (SWAT) model’s identifiability of the realistic spatial distribution of land use, soil type, and precipitation data. The spatial variability in small watersheds did not significantly affect the hydrographs at the watershed outlet, and the SWAT model was not able to identify more realistic sets of spatial data. A new populationbased heuristic called the Isolated Speciation-based Particle Swarm Optimization (ISPSO) was developed to enhance the explorability and the uniformity of samples in high-dimensional problems. The algorithm was tested on seven mathematical functions and outperformed other similar algorithms in terms of computational cost, consistency, and scalability. One of the test functions was the Griewank function, whose number of minima is not well defined although the function serves as the basis for evaluating multi-modal optimization algorithms. Numerical and analytical methods were proposed to count the exact number of minima of the Griewank function within a hyperrectangle. The ISPSO algorithm was applied to the SWAT model to evaluate the performance consistency of optimal solutions and perform uncertainty analysis in the Generalized Likelihood Uncertainty Estimation (GLUE) framework without assuming a statistical structure of modeling errors. The algorithm successfully found hundreds of acceptable sets of model parameters, which were used to estimate their prediction limits. The uncertainty bounds of this approach were comparable to those of the typical GLUE approach.

Field scale variability of soil texture can influence crop yield and movement of soil water in the field. The objective of this study was to investigate the spatial structure of soil texture in relation to the variability of nitrate-N leaching using geostatistics. Soil textural fractions showed strong spatial autocorrelations from surface to 60 cm depth. Random variability of soil texture increased with depth. Soil water content, as well as total carbon, total nitrogen and soil organic carbon of top 15 cm, also showed spatial autocorrelations similar to soil texture. Elevation, relative slope position and vertical distance to channel network showed significant influence on the distribution of soil texture. Soil texture at 90 cm depth correlated best with cumulative percolated water and cumulative nitrate leached in field lysimeters. Our results showed that soil layers with low hydraulic conductivity control the water and nitrate movement through the soil profile.

O radioisótopo cosmogênico \'ANTPOT.7Be\' é produzido por interações de partículas cósmicas com átomos da atmosfera, e vem sendo usado como traçador em estudos de erosão do solo e de processos climáticos. Após a formação, o \'ANTPOT.7Be\' liga-se as partículas dos aerossóis presentes na atmosfera e é depositado na superfície terrestre com outras espécies de isótopos cosmogênicos pelas chuvas. Devido à grande afinidade com as partículas do solo e a meia vida curta de 53,2 dias, este radioisótopo acompanha os processos erosivos do solo e pode ser usado como traçador para estimar taxas de erosão e deposição de sedimentos durante um evento de chuva isolado ou conjunto de eventos de chuva erosivos de curta duração. Uma hipótese fundamental para a avaliação da redistribuição do solo através do \'ANTPOT.7Be\' é a uniformidade da distribuição espacial do seu fallout. O método do \'ANTPOT.7Be\' foi elaborado recentemente e por isso aplicado em poucas situações, de forma que muitos assuntos em relação ao método ainda não foram propriamente estudados, e algumas hipóteses, como da uniformidade do fallout do \'ANTPOT.7Be\', precisam ser avaliadas. O principal objetivo deste estudo foi avaliar a distribuição espacial do fallout do \'ANTPOT.7Be\' analisando-se as atividades dos 5 mm iniciais da água da chuva de eventos isolados. Os eventos de chuva foram amostrados em doze pontos de coleta distribuídos em uma área experimental de aproximadamente 300 m² e localizada no campus da Universidade de São Paulo, em Piracicaba. As medidas de atividade do \'ANTPOT.7Be\' foram realizadas em um espectrômetro gama de eficiência relativa de 53%, pertencente ao laboratório de Radioisótopos do CENA. As atividades de \'ANTPOT.7Be\' na água da chuva dos eventos no período estudado variaram de 0,26 e 1,81 Bq.L-1, com as maiores atividades obtidas no verão e as menores na primavera. A variabilidade espacial das atividades na água da chuva apresentou valor elevado em cada um dos 5 eventos isolados, evidenciando a alta aleatoriedade da distribuição espacial dos valores de atividade. Através de uma simulação com os dados de variabilidade espacial obtidos neste trabalho e de inventários de referência citados na literatura, determinou-se a taxa de erosão mínima detectável pelo método do \'ANTPOT.7Be\'. Verifica-se a importância em se considerar um número representativo de amostras no levantamento do inventário médio de referência do \'ANTPOT.7Be\' no solo, essencial para precisão dos resultados de taxas de redistribuição do solo pelo método / The cosmogenic radionuclide beryllium-7 (\'ANTPOT.7Be\') is produced in the atmosphere by cosmic particle reactions and is being used as a tracer for soil erosion and climatic processes research. After the production, \'ANTPOT.7Be\' bonds to aerosol particles in the atmosphere and is deposited on the soil surface with other radionuclide species by rainfall. Because of the high adsorption on soil particles and its short half-life of 53.2 days, this radionuclide follows of the erosion process and can be used as a tracer to evaluate the sediment transport that occurs during a single rain event or short period of rain events. A key assumption for the erosion evaluation through this radiotracer is the uniformity of the spatial distribution of the \'ANTPOT.7Be\' fallout. The \'ANTPOT.7Be\' method was elaborated recently and due to its few applications, some assumptions related to the method were not yet properly investigated yet, and the hypothesis of \'ANTPOT.7Be\' fallout uniformity needs to be evaluated. The aim of this study was to evaluate the \'ANTPOT.7Be\' fallout spatial distribution through the rain water \'ANTPOT.7Be\' activity analysis of the first five millimeters of single rain events. The rain water was sampled using twelve collectors distributed on an experimental area of about 300 m², located in the campus of São Paulo University, Piracicaba. The \'ANTPOT.7Be\' activities were measured using a 53% efficiency gamma-ray spectrometer from the Radioisotope laboratory of CENA. The \'ANTPOT.7Be\' activities in rain water varied from 0.26 to 1.81 Bq.L-1, with the highest values in summer and lowest in spring. In each one of the 5 single events, the spatial variability of \'ANTPOT.7Be\' activity in rain water was high, showing the high randomness of the fallout spatial distribution. A simulation using the \'ANTPOT.7Be\' spatial variability values obtained here and \'ANTPOT.7Be\' average reference inventories taken from the literature was performed determining the lowest detectable erosion rate estimated by \'ANTPOT.7Be\' model. The importance of taking a representative number of samples to determine the average reference \'ANTPOT.7Be\' inventory was verified, which is essential to improve the precision of the soil redistribution rate estimates

Spatial variability of rainfall is a significant factor in hydrologic and water quality modeling. In recent years, characterizing and analyzing the effect of spatial variability of rainfall in hydrologic applications has become vital with the advent of remotely sensed precipitation estimates that have high spatial resolution. In this study, the effect of spatial variability of rainfall in hourly runoff generation was analyzed using the Soil and Water Assessment Tool (SWAT) for Big Sandy Creek and Walnut Creek Watersheds in North Central Texas. The area of the study catchments was 808 km2 and 196 km2 for Big Sandy Creek and Walnut Creek Watersheds respectively. Hourly rainfall measurements obtained from raingauges and weather radars were used to estimate runoff for the years 1999 to 2003. Results from the study indicated that generated runoff from SWAT showed enormous volume bias when compared against observed runoff. The magnitude of bias increased as the area of the watershed increased and the spatial variability of rainfall diminished. Regardless of high spatial variability, rainfall estimates from weather radars resulted in increased volume of simulated runoff. Therefore, weather radar estimates were corrected for various systematic, range-dependent biases using three different interpolation methods: Inverse Distance Weighting (IDW), Spline, and Thiessen polygon. Runoff simulated using these bias adjusted radar rainfall estimates showed less volume bias compared to simulations using uncorrected radar rainfall. In addition to spatial variability of rainfall, SWAT model structures, such as overland flow, groundwater flow routing, and hourly evapotranspiration distribution, played vital roles in the accuracy of simulated runoff.

This thesis investigates variability in airway caliber and the distribution of ventilation within the human lung as thought to occur in asthma. Currently, the understanding of how an integrated network of airways can lead to temporal and spatial variation as found in the human lung is unclear. Throughout this thesis, a multibranch airway tree model was used in a forward modeling approach. In a variability study, the mean airway resistance (RL) was observed to be proportional to the standard deviation in airway resistance (SDRL) as reported in the literature under several conditions of airway diameter indicating the strong robustness of this behavior. The model predicted previously reported RL distributions and the reported proportionality of SDRL and RL, but only when we included coherency between airways. In a second study, patient specific ventilation was investigated using an image functional approach by closing specific airways (creating defects) identified by hyperpolarized 3He MRI from asthmatic subjects. Impedance predictions from the imposed heterogeneous ventilation were then calculated and correlated to 3He MRI ventilation defect percent (VDP), plethysmography, and spirometry data. These predictions suggest the forced oscillation technique (FOT) to be a superior metric toward the evaluation of the VDP. In a third study, we investigated how asymmetric branching could play a role in ventilation defect emergence and persistence. At high muscle activation levels simulating an asthmatic episode, airway trees with greater asymmetry reached steady state sooner, with defects that were more persistent in location, had lower RL values (~50%), and greater EL values (~25%) after bronchoconstriction. These results suggest the initial formation of ventilation defects was dependent on airway instability; however, the location and persistence of ventilation defects may be due to geometric airway structure. By modeling the contribution of ventilation defects to lung impedance, we were able to show that defects can play a role in governing the relationship between RL and its variation, and the effect of defects through VDP could be better assessed using FOT. Moreover, lung structure contributed to the emergence and persistence of ventilation defects, meaning that defects could be potentially ameliorated through structural intervention.

O radioisótopo cosmogênico \'ANTPOT.7Be\' é produzido por interações de partículas cósmicas com átomos da atmosfera, e vem sendo usado como traçador em estudos de erosão do solo e de processos climáticos. Após a formação, o \'ANTPOT.7Be\' liga-se as partículas dos aerossóis presentes na atmosfera e é depositado na superfície terrestre com outras espécies de isótopos cosmogênicos pelas chuvas. Devido à grande afinidade com as partículas do solo e a meia vida curta de 53,2 dias, este radioisótopo acompanha os processos erosivos do solo e pode ser usado como traçador para estimar taxas de erosão e deposição de sedimentos durante um evento de chuva isolado ou conjunto de eventos de chuva erosivos de curta duração. Uma hipótese fundamental para a avaliação da redistribuição do solo através do \'ANTPOT.7Be\' é a uniformidade da distribuição espacial do seu fallout. O método do \'ANTPOT.7Be\' foi elaborado recentemente e por isso aplicado em poucas situações, de forma que muitos assuntos em relação ao método ainda não foram propriamente estudados, e algumas hipóteses, como da uniformidade do fallout do \'ANTPOT.7Be\', precisam ser avaliadas. O principal objetivo deste estudo foi avaliar a distribuição espacial do fallout do \'ANTPOT.7Be\' analisando-se as atividades dos 5 mm iniciais da água da chuva de eventos isolados. Os eventos de chuva foram amostrados em doze pontos de coleta distribuídos em uma área experimental de aproximadamente 300 m² e localizada no campus da Universidade de São Paulo, em Piracicaba. As medidas de atividade do \'ANTPOT.7Be\' foram realizadas em um espectrômetro gama de eficiência relativa de 53%, pertencente ao laboratório de Radioisótopos do CENA. As atividades de \'ANTPOT.7Be\' na água da chuva dos eventos no período estudado variaram de 0,26 e 1,81 Bq.L-1, com as maiores atividades obtidas no verão e as menores na primavera. A variabilidade espacial das atividades na água da chuva apresentou valor elevado em cada um dos 5 eventos isolados, evidenciando a alta aleatoriedade da distribuição espacial dos valores de atividade. Através de uma simulação com os dados de variabilidade espacial obtidos neste trabalho e de inventários de referência citados na literatura, determinou-se a taxa de erosão mínima detectável pelo método do \'ANTPOT.7Be\'. Verifica-se a importância em se considerar um número representativo de amostras no levantamento do inventário médio de referência do \'ANTPOT.7Be\' no solo, essencial para precisão dos resultados de taxas de redistribuição do solo pelo método / The cosmogenic radionuclide beryllium-7 (\'ANTPOT.7Be\') is produced in the atmosphere by cosmic particle reactions and is being used as a tracer for soil erosion and climatic processes research. After the production, \'ANTPOT.7Be\' bonds to aerosol particles in the atmosphere and is deposited on the soil surface with other radionuclide species by rainfall. Because of the high adsorption on soil particles and its short half-life of 53.2 days, this radionuclide follows of the erosion process and can be used as a tracer to evaluate the sediment transport that occurs during a single rain event or short period of rain events. A key assumption for the erosion evaluation through this radiotracer is the uniformity of the spatial distribution of the \'ANTPOT.7Be\' fallout. The \'ANTPOT.7Be\' method was elaborated recently and due to its few applications, some assumptions related to the method were not yet properly investigated yet, and the hypothesis of \'ANTPOT.7Be\' fallout uniformity needs to be evaluated. The aim of this study was to evaluate the \'ANTPOT.7Be\' fallout spatial distribution through the rain water \'ANTPOT.7Be\' activity analysis of the first five millimeters of single rain events. The rain water was sampled using twelve collectors distributed on an experimental area of about 300 m², located in the campus of São Paulo University, Piracicaba. The \'ANTPOT.7Be\' activities were measured using a 53% efficiency gamma-ray spectrometer from the Radioisotope laboratory of CENA. The \'ANTPOT.7Be\' activities in rain water varied from 0.26 to 1.81 Bq.L-1, with the highest values in summer and lowest in spring. In each one of the 5 single events, the spatial variability of \'ANTPOT.7Be\' activity in rain water was high, showing the high randomness of the fallout spatial distribution. A simulation using the \'ANTPOT.7Be\' spatial variability values obtained here and \'ANTPOT.7Be\' average reference inventories taken from the literature was performed determining the lowest detectable erosion rate estimated by \'ANTPOT.7Be\' model. The importance of taking a representative number of samples to determine the average reference \'ANTPOT.7Be\' inventory was verified, which is essential to improve the precision of the soil redistribution rate estimates

Spatial variations in soil properties can directly affect Nitrogen status of corn (Zea mays L.) and decrease efficiency of uniform fertilizer N applications. The objective of this study was to assess the spatial variations of soil properties and measure the effect on corn Nitrogen status through canopy reflectance. Field trials were conducted in 2010 and 2011 on a producer’s field west of Yazoo City, MS that contained high in field variability. Soil physical and chemical properties all exhibited moderate to high spatial dependency during both years of this study. Vegetative indices were derived from canopy reflectance values and indices utilizing the red-edge were the strongest and most consistent descriptors of tissue N percent and whole plant N uptake. The Canopy Chlorophyll Content Index (I) shows the greatest potential of assessing variations of corn Nitrogen status among the indices tested.

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