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Orientadores: Stanley Robson de Medeiros Oliveira, Ana Maria Heuminski de Avila / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Agrícola / Made available in DSpace on 2018-08-22T14:12:46Z (GMT). No. of bitstreams: 1 Dourado_CamiladaSilva_M.pdf: 21521693 bytes, checksum: d0c749dfa3c77ac47a96acd234b8d3c3 (MD5) Previous issue date: 2013 / Resumo: O conhecimento das condições climáticas, identificando regiões com maiores riscos de ocorrências de eventos extremos, que possam impactar os diversos setores socioeconômicos e ambientais, tornou-se um grande desafio. No Brasil as maiores ocorrências de eventos extremos estão relacionadas aos fenômenos hidrológicos. Em particular, o estado da Bahia apresenta alta variabilidade temporal e espacial no clima, desde áreas consideradas áridas ou com risco de aridização (ao Norte) a regiões com clima úmido na faixa litorânea. O estado tem sido alvo nesses últimos anos de diferentes eventos extremos de chuva, com enchentes em algumas áreas e secas severas em outras. Neste contexto, o objetivo deste trabalho foi utilizar técnicas de mineração de dados para analisar a frequência das ocorrências dos eventos extremos de precipitação durante o período de 1981 a 2010 no estado da Bahia, com o propósito de subsidiar a tomada de decisão referente a ações preventivas e mitigadoras dos impactos socioeconômico e ambientais. Para isto, foram utilizados dados climáticos de precipitação fornecidos pelo Sistema de Informações Hidrológicas da Agência Nacional de Águas. Aplicando-se a tarefa de agrupamento (clusterização), por meio do algoritmo k-means, as séries históricas de dados climáticos foram agrupadas em cinco zonas pluviometricamente homogêneas. Posteriormente, foram realizadas análises em diferentes escalas temporais (anual, mensal e diária) identificando através da Técnica dos Quantis limiares superiores e inferiores de intensidade de chuva em cada região homogênea, para cada escala temporal. Na escala mensal, foram identificados padrões sequenciais das ocorrências dos eventos extremos positivos e negativos ao longo dos trinta anos. Os resultados reforçam a potencialidade da técnica de mineração de dados em agrupar zonas homogêneas por similaridade pluvial, com o uso do algoritmo k-means. Revelam ainda, para todas as escalas temporais utilizadas, uma alta variabilidade pluviométrica. Os anos registrados com maior ocorrência de eventos extremos negativos estão na década de 90 e os anos registrados com mais eventos extremos positivos na década de 2000 / Abstract: The knowledge of climate conditions, identifying areas with the greatest risk of occurrence of extreme events, that may impact the various socioeconomic and environmental sectors, has become a major challenge. In Brazil the largest occurrences of extreme events are related to hydrological phenomena. In particular, the state of Bahia presents a high temporal and spatial variability of climate, from areas considered arid or with risk to become arid - (in the North) to regions with humid along the coast. The state has been targeted of different extreme rainfall events recently, with floods in some areas and severe droughts in others. In this context, the aim of this study was to use data mining techniques to analyze the frequency of occurrences of extreme precipitation events during the period from 1981 to 2010 in the state of Bahia, in order to support decision making regarding the preventive and mitigative environmental and socioeconomic impacts. To accomplish that, it was used climate data of precipitation supplied by the Hydrological Information System of the National Water Agency. By applying the task of grouping (clustering) by means of the k-means algorithm, the time series of climate data were grouped into five homogeneous rainfall zones. Subsequently, analyzes were performed on different time scales (annually, monthly and daily) identifying by quantile methods the upper and lower thresholds of rainfall intensity in each homogeneous region, for each time scale. At the monthly scale, sequential patterns of occurrences of extreme positive and negative events were identified over the thirty years. The results reinforce the potential of the data mining technique to group homogeneous zones by similarity of rain, using the k-means algorithm. They also reveal, for all time scales used, high rainfall variability. The years with the highest recorded extreme negative events are in the 90's and those registered with more extreme positive events are in the 2000's / Mestrado / Planejamento e Desenvolvimento Rural Sustentável / Mestra em Engenharia Agrícola

The effect of altitude on individual storm precipitation in some of the San Dimas experimental watersheds is investigated. It is found that there is a well- defined increase of storm precipitation with altitude for storms greater than one inch. This increase is a linear function of storm depth. Using 41 storms of different magnitudes, a precipitation -altitude relationship is derived for a small area in the San Dimas Experimental Forest. The regionalization of this relationship and its transferability are tested by analyzing differences (errors) between computed and observed storm precipitation values in each case. In testing the regionalization of the precipitation- altitude relationship by computing mean areal storm precipitation over a larger area the standard error of estimate is around 11 percent. In transfering the same relationship the results are not as good and give a standard error of 16 percent. For individual points, however, the error is much higher. A rainfall- runoff model is used as a tool for evaluating the effect of precipitation errors, on simulated streamflow, in a watershed of 4.5 square miles. For annual flows, errors range between 3.4 and 12.3 percent while errors in simulated monthly flows are as high as 22 percent. It is also evident that there is a strong dependence of the error magnitude on the state (wet, dry, etc.) of the preceding year or months, whichever is applicable. An error propagation is observed as a result of consistently over -estimating the precipitation input to the model. This evaluation is more of a qualitative nature and the values of error given should be viewed in this sense.

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Nutrient ion exchange was examined between simulated acid rain solutions and northern red oak (Ouercus rubra L.) leaves of trees growing in fertile, limestone-derived soil and less fertile, sandstone/shale-derived soil. Leaves harvested from trees growing on the fertile site had greater concentrations of total N, P, K, Ca, and Mn but less total Mg than leaves of trees on the less fertile site. Cation losses from leaves of both sites were similar when exposed T3 to simulated rain solutions of pH 5.6, 4.3, and 3.0. Simulated rain solutions of pH 3.0 leached the greatest amount of total cations from leaves of both sites. Differences in acidity between leachates and starting rain solutions increased as the acidity of starting solutions contacting leaves of either site increased. Differences in leaf nutrient status between sites typically did not affect leachate acidity. Hydrogen ion exchange, believed to be the main mechanism of cation loss from leaves of both sites, accounted for 30 to 44% of all cations leached from leaves of both sites. Concentrations of inorganic ions were measured in bulk rainfall and bulk throughfall collected beneath northern red oak trees growing on the fertile and less fertile sites. Rainfall passing through crowns at both sites was enriched with S0₄²⁻, P0₄³⁻, Ca²⁺, Mg²⁺, K⁺, Mn²⁺, and Fe²⁺, but lost NH₄⁺ to the crowns. There was little difference in the inorganic chemistry of incident rainfall between sites. Large-particle dryfall ionic concentrations, rainfall volume, and leaf area were all larger at the fertile than at the less fertile site. Higher concentrations of Ca²⁺, Mg²⁺, NH₄⁺, Mn²⁺, and S0₄²⁻in throughfall at the fertile site compared to that of the less fertile site are likely due to the combination of these three factors. Historical northern red oak crown areas were estimated for the fertile and less fertile sites by a two step procedure using annual growth ring chronologies and published regression equations. These equations related total crown area to total crown dry weight. The usefulness of crown area estimates in throughfall studies was demonstrated by applying nutrient ion exchange data, collected beneath northern red oak crowns in 1984, to 1982 and 1930 crown area estimates. Smaller nutrient ion exchange estimates in 1930 were due to smaller crown area estimates. / Ph. D.

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A comprehensive hydrological study of large watersheds in Africa e.g. the Congo basin and the Nile basin has not been vigorously pursued for various reasons. One of the major reasons is the lack of adequate modeling tools that would not be very demanding in terms of input data needs and yet inclusive enough to cover such wide extents (over 3 million square kilometers for the Congo basin). Using a coupled run of the Community Atmospheric model (CAM3) and Community Land Model (CLM3) components of the Community Climate System of Models (CCSM), this study looks into the spatial and temporal variation of precipitation and river runoff in the Congo basin in the light of increasing trends in deforestation of the tropical forests. The effect of deforestation on precipitation and runoff is investigated by changing the land cover-type from the current configuration of broadleaf evergreen/deciduous, non-Artic grass and corn to a mostly grass type of vegetation. Discharge simulation for the river Congo is centered at the point of entrance to the Atlantic Ocean. Although the CLM3 does not presently simulate the observed river runoff to within at least one standard deviation it gives an opportunity to iteratively improve on the land surface parameterization with a possibility of future accurate prediction of mean monthly river runoffs under varying climate scenarios and land use practices. When forced with the National Center for Environment and Prediction (NCEP) re-analysis data the CLM3 runoff simulation results are relatively more stable and much closer to the observed. An improved CLM3 when coupled to CAM3 or other Global Climate Models is definitely a better tool for investigative studies on the regional hydrological cycle in comparison to the traditional methods. There was a slight reduction in rainfall in the first experiment which mimicked a severe form of deforestation and a slight increase in rainfall following low level of deforestation. These changes in rainfall were however statistically insignificant when compared to the control simulation. There was notable heterogeneity in the spatial distribution of the changes in rainfall following deforestation.

Mémoire (M.Eng.)-- Université du Québec à Chicoutimi, 1994. / Document électronique également accessible en format PDF. CaQCU

MENVSC / Department of Geography and Geo-Information Sciences / Out of all rain-producing weather systems, cut-off lows (COLs) are linked with the occurrence of high impact rainfall and in some cases short-lived floods which can last for 24 hours over South Africa. This study examined the characteristics associated with the present occurrence of the severe COL systems over South Africa from 2011 to 2017. The accuracy of the 4.4 km Unified Model (UM) which is currently in use for simulating areas of deep moist convection in South Africa was evaluated. The UM simulated geopotential height at 500 hPa as well as the associated 24 hours precipitation which were compared against the daily fields of geopotential height and 6-hourly precipitation from the European Centre for Medium-Range Weather Forecasts (ECMWF). COL events were categorized and analyzed according to the associated surface circulation patterns at 850 hPa. The seasonal distribution and duration of the systems over northern (10°E-33°E //22°-32°S) and southern (10°E-33°E //32°-35°S) regions of the study area were also analyzed. Results show COL systems shifting with season towards the north eastern parts of the country, with an increased number of events during the austral winter season during the study period. Systems which lasted for long time were observed during the austral winter and spring seasons. The UM tends to simulate areas of heavy precipitation accurately with poor simulation during the initial stages of the systems. The UM provided a more realistic-looking closed geopotential height and rainfall fields for systems which are coupled with a cold front at the surface. Application of the knowledge about the evolution in the characteristics of COL events from this study can improve the operational forecasting of these weather systems over the country. / NRF

M. S.