Análise da distribuição temporal das chuvas em eventos hidrológicos extremos / The analysis of time distribution of rainfall in heavy storms

RESUMO: O objetivo da pesquisa foi analisar a influência da distribuição temporal das chuvas em eventos hidrológicos extremos na bacia do Córrego do Gregório (São Carlos, São Paulo). Foram aplicadas duas metodologias de distribuição temporal das chuvas e adotados períodos de retorno de 25, 50 e 100 anos: o método de Huff 1º quartil e o método dos blocos alternados; e simularam-se as manchas de inundação com o software HEC-GeoRAS. A alteração do método de distribuição temporal das chuvas resultou em hidrogramas com diferenças de até 46% na vazão de pico, 57% nas áreas da mancha de inundação da região e 1,5 m na altura de inundação.

ABSTRACT: The research objective was to analyze the time distribution of rainfall caused by flash floods in Gregorio watershed (São Carlos, São Paulo, Brazil). Two methodologies of temporal distribution of rainfall were applied for adopted return periods of 25, 50 and 100 years: the Huff 1st quartile method and the alternating blocks method; wherein the flood inundation areas were simulated with HEC-GeoRAS software. The time distribution of both rainfall methods exhibit 46% discrepancy in peak flow, 57% in flood inundation area and 1.5 m in water depth.

Two-Dimensional Hydrodynamic Modelling of Flood Inundation for a Part of the Mekong River with TELEMAC-2D.

Aims: This paper presents a study on the development of a 2-dimensional (2D) hydrodynamic model based on TELEMAC-2D for the flood simulation of the river from Kratie to Kampong Cham in Cambodia, a part of the Mekong River. The motivation behind the research was to study the feasibility of TELEMAC-2D in flood forecasting, and specifically to determine its adequacy in flood simulations with a focus on the reduction in model run-time through parallelization. Place and Duration of Study: DHI-NTU Centre, Nanyang Environment and Water Research Institute (NEWRI), Nanyang Technological University, between November 2013 and March 2014. Methodology: We simulated an actual flood event which occurred between June to November in 2001 for the stretch of the Mekong River from Kratie to Kampong Cham and compared the model simulations with MODIS satellite Images for specific days in the pre-, peak- and post-flood period. Results: It was found that during the peak-flood period, there was high percentage (> 90%) match between the simulation results and observation obtained from satellite images while the match was below 50% for the pre- and post- flood periods. Conclusion: The 2D simulation results were consistent with observations from satellite imaging. The discrepancy at pre- and post-flood may be due to the fact that (i) the model takes into account only hydrodynamic processes of flows in the river and flood plain, it does not consider other hydrological processes such as infiltration or evaporation which may be important during the preand post- flood periods, and (ii) the resolution of MODIS satellite image at 500m x 500m may be too coarse and therefore not sufficient to identify flooded areas when the area is small or water depth low. Finally, it was found that the computing time can be reduced significantly with parallelization using multi-core processors, albeit with lesser advantage in speedup when the number of cores increased beyond 4.

Nest plasticity of Cornitermes silvestrii (Isoptera, Termitidae, Syntermitinae) in response to flood pulse in the Pantanal, Mato Grosso, Brazil

Nest plasticity of Cornitermes silvestrii (Isoptera, Termitidae, Syntermitinae) in response to flood pulse in the Pantanal, Mato Grosso, Brazil. The Pantanal is one of the largest wetlands in the world. Since many areas in Pantanal are flooded during part of the year, it is expected that plants and animals would have mechanisms for their survival during the flooded period. This study investigated the existence of differences in nest shape and inquilines of Cornitermes silvestrii in areas influenced by the flood pulse. We measured the volume, height, width, and height/width ratio of 32 nests in flooded areas and 27 in dry areas, and performed an one-way-Anova with the quasi-Poisson distribution to determine if there were differences in the nest measurements between the points. To analyze the relationship of nest inquilines to flood pulse and nest shape, we performed a regression with a Poisson distribution with the inquiline richness and flood pulse, and the above measurements. The nests of C. silvestrii in flooded areas were significantly higher than nests in dry areas, and had a larger height/width ratio. Colonies in periodically flooded areas would probably make a larger effort to extend their nests vertically, to maintain at least some portion of the structure out of the water and prevent the entire colony from being submerged. Neither the size of the nest nor the flood pulses influenced the assemblage of 11 species found in nests of C. silvestrii.

Distribución geográfica de casos de fiebre de dengue en zonas anegadas de Villahermosa, Tabasco, México, 2010 / Geographic distribution of dengue fever cases in flooded zones from Villahermosa, Tabasco, in 2010

Objective: To describe the geographical distribution of dengue fever cases in flooded areas of Villahermosa, Tabasco, in 2010. Methods: Cross-sectional, descriptive study. Universe: Colonies with antecedents of flooding during the inundation of the State, located in Villahermosa, Tabasco: Gaviotas Norte, Gaviotas Sur, La Manga 1th Section, La Manga 2nd Section and La Manga 3th Section. Convenience sample without randomization. Variables: location, dengue fever case. Analysis: descriptive statistic. Software: SPSS version 11.0. Results: 540 individuals were included. The distribution was: Gaviotas Norte, 36.1%; Gaviotas Sur, 24.8%; La Manga 1th Section, 13.8%; La Manga 2nd Section, 13.2%; and La Manga 3th Section, 12.1%. We found three cases with positive serology of IgG (0.6%) and five cases of positive IgM (0.9%). The geographical distribution was associated with the proximity to two water bodies: Rio Grijalva and Laguna El Encanto. Conclusions: It is necessary to reinforce preventive interventions in the proximity of bodies of fresh water.

Objetivo: Describir la distribución geográfica de los casos de fiebre de dengue en zonas anegadas de Villahermosa, Tabasco, México, en el año 2010. Métodos: Estudio transversal, descriptivo. Universo en estudio: colonias con antecedentes de anegación durante las inundaciones del Estado, ubicadas en Villahermosa, Tabasco: Gaviotas Norte, Gaviotas Sur, La Manga 1ª Sección, La Manga 2ª Sección y La Manga 3ª Sección. Muestra: no probabilís-tica por conveniencia. Variables: ubicación, caso de fiebre de dengue. Análisis: estadística descriptiva. Software: SPSS versión 11.0. Resultados: Se incluyeron 540 sujetos, distribuidos en Gaviotas Norte 36,1%; Gaviotas Sur 24,8%; La Manga 1a Sección 13,8%; La Manga 2a Sección 13,2%; La Manga 3a Sección 2,1%. Se encontraron tres casos con serología positiva a IgG (0,6%) y cinco casos con serología positiva a IgM (0,9%). La distribución geográfica de los casos guardó relación con la cercanía a dos cuerpos de agua: Río Grijalva y Laguna El Encanto. Conclusiones: Es necesario reforzar las intervenciones preventivas en zonas cercanas a cuerpos de agua dulce.

Resistência á submersão de ácaros (Acari: Ribatida) terrestres de florestas inundáveis e de terra firme na Amazônia central em condições experimentais de laboratório

Specimens of Rostrozetes foveolatus were obtained from two inundated forest areas ("várzea" and "igapó") and from two nonflooded secondary forests in the Central Amazon Region. The survival rates of their populations under submerged and nonsubmerged conditions were compared in laboratory conditions. The "igapó" population was sampled during three periods in 1992: before (February: litter nonsubmerged), in the beginning (April: litter submerged) and in the peak of the inundation phase (July: litter submerged). At "igapó", the animals survived better when submitted to nonsubmerged conditions, meaning that submersion is a stress factor. The same result did not occur at "várzea", signifying a better adaptation of this population to the submersion stress. The lowest flood resistance (27 days) was found in animals from "terra firme" secondary forest, away from the igapó. A considerable submersion resistance in the population sampled in the secondary forest, near the igapó forest, was comparable to the populations of the inundated areas and greater than the resistence at "terra-firme", far away from the "igapó". Animals sampled in February of 1996 (reared individually in plastic containers), from the flooded forests had significantly higher survival rates than those from secondary forests. Three situations in relation to the submersion period were registered: a) one of "várzea", with a more resistant population, b) one of "igapó", with a intermediate resistance and c) one of "terra-firme", away from the "igapó", with a lower resistant population. In twelve of the fifteen species studied, a high resistance to submersion was also registered.

Espécimens de Rostrozetes foveolatus foram obtidos de duas florestas inundáveis (várzea e igapó) e de duas florestas secundárias (terra firme) da Amazônia Central. As populações foram comparadas para a obtenção da taxa de sobrevivência em experimentos de laboratório nas condições submersas e não submersas. As coletas no igapó foram efetuadas em três períodos de 1992: antes (fevereiro: serapilheira não submersa), no início (abril: serapilheira submersa) e no pico da inundação (julho: serapilheira submersa). No igapó, os animais sobreviveram melhor em condição não submersa, significando que a submersão é um fator de estresse. O mesmo não ocorreu na várzea, indicando que esta população está melhor adaptada ao estresse da submersão. A menor resistência à submersão (27 dias) foi registrada nos animais de uma floresta secundária da terra firme, situada longe do igapó. Na população da terra firme próxima ao igapó, a resistência a submersão foi comparável à registrada para as populações das áreas inundáveis e maior do que a registrada em terra firme longe do igapó. Em experimentos com animais coletados em fevereiro de 1996 (mantidos individualmente em recipientes plásticos), as populações das florestas inundáveis tiveram taxa de sobrevivência significativamente maior em relação aos das florestas não inundáveis. Três situações foram registradas quanto a resistência à submersão: a) a da várzea, com população mais resistente, b) a do igapó, com uma população intermediária e c) a da terra-firme longe do igapó, com uma população menos resistente. Em doze das outras quinze espécies estudadas foi registrada alta resistência às condições de submersão.

Estratégias de sobrevivência de invertebrados terrestres em florestas inundáveis da amazônia central: uma resposta à inundação de longo período

Inundation forests in Central Amazonia and their adjacent shores are covered by several meters of flood water for 5-7 months each year, due to the monomodal periodic flood pulse of rivers. Terrestrial invertebrates have adapted to this ecosystem by evolving several survival strategies. The fauna comprises both, terricolous and arboricolous animals. Both groups include non-migrants and migrants. Migratory reaction of terricolous animals is horizontal (following the high-water line), vertical (temporal ascent to trunk or canopy of trees) or includes a temporal flight to upland forests. Non-migrants have active or dormant stages under water. The latter pass inundation in naturally available retreats, in self-made retreats or as eggs. Non-migrant arboricolous animals reproduce and live exclusively in the trunk and canopy region, whereas migrants include life stages that live on the ground as well. Characteristics and examples of species are given for each of these categories. The flood pulse is regarded as the original determinant of migration. However, most invertebrates have become sensitive to secondary, mainly abiotic factors. Only in a few species is migration still directly related to the cycle of flooding.

As florestas inundáveis na Amazônia Centrai e suas margens adjacentes sofrem alagações de vários metros de altura por 5-7 meses cada ano, devido ao pulso monomodal de inundação dos rios. Os invertebrados terrestres adaptaram-se à este ecossistema, envolvendo várias estratégias de sobrevivência. A fauna compõe-se de animais terrícolas e arborícolas. Ambos os grupos incluem não migrantes e migrantes. A reação migratória dos animais terrícolas é horizontal (à frente da linha d'água), vertical (subida temporária para troncos ou copas de árvores) ou inclui um vôo temporário para florestas de terra firme. Não migrantes têm estágios ativos ou dormentes abaixo d'agua. Os dormentes passam a inundação em abrigos disponíveis em condições naturais, em abrigos fabricados ou cm estágio de ovo. Animais arborícolas não migrantes vivem e se reproduzem exclusivamente em troncos e copas das árvores, enquanto que os migrantes tem estágios de desenvolvimento os quais vivem também no chão. São dadas as características e exemplos de espécies para cada uma destas categorias. O pulso de inundação é considerado como determinante original da migração. Entretanto, a maioria dos invertebrados se tornaram sensíveis aos ecofatores secundários, na sua maioria abióticos. Somente em algumas espécies, a migração ainda é diretamente relacionada com o pulso de inundação.