Made available in DSpace on 2014-07-29T15:01:49Z (GMT). No. of bitstreams: 1 METODO PARA A DETERMINACAO DO FATOR.PDF: 2167463 bytes, checksum: 01a16749c59f2e7aa42c668adc5ce053 (MD5) Previous issue date: 2012-06-18 / The main objective of this work was to develop an empirical areal reduction factor - ARF - determination method for urban basins, which is a coefficient applied to average rainfall estimates for projects, given rainfall at a point. After a review about the subject, it was verified the needs of developing regional studies and the existence of some deficienes on current approaches. In this sense, it was tried to create an appropriate methodology given the spatial variability of extreme rainfall on urban basins. Therefore, the new suggested method, differently from the observed in others techniques, is primarily based on objective assessment of the ratio between extreme average rainfall calculated above several areas and the extreme point rainfall observed in gauges located in the center of those areas. After structuring it, the proposed method was tested in a pilot implementation with data obtained from a new raingauge network in the region of Córrego Botafogo Basin's, urban zone of Goiânia. The results were analyzed as to the dependence of ARF to area, duration and exceedance probability. It was found a strong relation with area, a minor with duration and the need of further studies about the exceedance probability influence. Lastly, the ARF values obtained with results fitting were compared with those indicated from other employed empirical models. From this study, it can be concluded that proposed methodology is appropriated to determine ARF, as its results are compatibles with assumptions established. However, new studies are needed, with a greater amounts of data, to obtain practical results. / O objetivo deste trabalho foi desenvolver um método empírico para determinação do fator de redução de área - FRA - em bacias urbanas, coeficiente empregado na estimativa de chuvas de projeto médias a partir de chuvas de projeto pontuais. Após uma revisão sobre o tema na literatura existente, foi verificada a necessidade do desenvolvimento de estudos regionais e a existência de lacunas nas atuais abordagens sobre o tema. Neste sentido, buscou-se elaborar uma metodologia adequada à variabilidade espacial dos eventos extremos usuais em bacias urbanas. Assim sendo a nova metodologia sugerida, diferentemente do observado nas demais técnicas, se baseia fundamentalmente na avaliação objetiva da razão entre as chuvas extremas calculadas sobre diversas áreas e as chuvas extremas observadas nos postos centrais à estas áreas. Após sua estruturação, o modelo proposto foi testado em uma implementação piloto com dados de uma rede pluviográfica recém instalada na região da Bacia do Córrego Botafogo, zona urbana de Goiânia. Os resultados obtidos da aplicação direta da metodologia foram então analisados quanto à dependência do FRA em relação às variáveis área, duração e período de retorno. Dos testes realizados, foi possível identificar uma forte dependência do comportamento estatístico dos resultados em relação à variação da área, uma dependência em relação à duração e a necessidade de estudos mais elaborados em relação ao período de retorno. Por fim, os valores de FRA obtidos após ajustes dos resultados foram comparados com os valores indicados por métodos empíricos mais difundidos. Dos estudos, concluí-se que a metodologia proposta é adequada para a obtenção do FRA, bem como seus resultados são compatíveis com os pressupostos pré-estabelecidos. Há no entanto a necessidade de novos estudos, com maior quantidade de dados, para a obtenção de resultados aplicáveis na prática.

The fine-scale structure of global (30N-30S) tropical rainfall is characterised using 13 years (1998-2010) of 3-hourly and daily, 0.25-degree Tropical Rainfall Measuring Mission (TRMM) 3B42 rainfall product. At the outset, the dominant timescales present in rainfall are identified. Specifically, the Fourier spectrum (in time) is estimated in two ways (a) spectrum of spatially averaged (SoSA) rainfall; and (b) spatial average of the spectrum (SAoS) of rainfall at each grid point. This procedure is applied on rainfall at the 3-hourly and daily temporal resolutions. Both estimates of the spectrum show the presence of a very strong seasonal cycle. But, at subseasonal timescales, the two methods of estimating spectrum show a marked difference in daily rainfall. Specifically, with SoSA the variability peaks at a subseasonal timescale of around 5 days, with a possible secondary peak around 30-40 days (mostly in the southern tropics). With SAoS, the variability is distributed across a range of timescales, from 2 days to 90 days. However, with finer resolution (3-hourly) observations, it is seen that (besides the seasonal cycle) both methods agree and yield a dominant diurnal scale. Along with other subseasonal scales, the contribution and geographical distribution of diurnal scale variability is estimated and shown to be highly significant. Given its large contribution to the variability of tropical rainfall, the diurnal cycle is extracted by means of a Fourier-based filtering and analysed. The diurnal rainfall anomaly is constructed by eliminating all timescales larger than 1 day. Following this, taking care to avoid spurious peaks associated with Gibbs oscillations, the time of day (called the peak octet) when the diurnal anomaly is largest is identified. The peak octet is estimated for each location in the global tropics. This is repeated for 13 years, and the resulting mode of the time of maximum rainfall is established. It is seen that (i) most land regions receive rainfall during the late afternoon/early evening hours; (ii) rainfall over open oceans lack a dominant diurnal signature with a possible combination of early morning and afternoon showers; (iii) coastal regions show a clear south/southwest propagation in the mode of the peak octet of rainfall. In addition to being a comprehensive documentation of the diurnal cycle at very fine scales, the results serve as a critical test for the validation of theoretical and numerical models of global tropical rainfall.