Joseilson Oliveira Rodrigues

Biophysics variables seasonality on surface in semiarid regions by using remote sensing

To investigate the rainfall regime effects over the albedo, NDVI (normalized difference vegetation index), net radiation and soil heat flux in a semiarid region (Northeast of Brazil), a study in the Trussu watershed was developed by using remote sensing. The study focuses on two images (Landsat 7 ETM+) provided by Instituto Nacional de Pesquisas Espaciais (INPE), from October 25, 2000 and July 24, 2001, each of them having a different rainfall regime (dry and wet seasons). The images were analyzed by using the SEBAL algorithm (surface energy balance algorithm for land). The results showed that the amount of rainfall affected the investigated variables, and the highest values of albedo were registered during the dry season. The NDVI presented high sensibility to rainfall regime, pointing out a high vegetation potential recover during the rainfall season. The NDVI along the Trussu River was up to 0.39, expressing the repair zone preservation. The watershed vegetation showed a high resilience power expressed by NDVI values in the year of 2001. Net radiation and soil heat flux were greater in the dry season, in this way expressing the effect of humidity on the energy balance.

Impacto da lixiviação de nitrato e cloreto no lençol freático sob condições de cultivo irrigado

Environmental impacts of nitrogenous fertilizers, pesticides and salts contained in irrigation are becoming an increasing concern, because they may move with soil water from root zone to groundwater. The aim of this research was to identify the irrigation management and the rainfall depth influence over nitrate and chloride concentration in the soil profiles, as well as the risk of water table pollution in the Irrigated District of Baixo Acarau (DIBAU), Ceara, Brazil. Soil samples were taken each 50cm deep soil profiles until to saturated zone (7m) in two different types of land use: irrigated area (S1) and native area (S2). Samples occurred during irrigation activities (Nov/06) and rainfall season (May/07). The water table was measured, monthly, from Dec/2003 to Nov/2005, Nov/2006, Mar and April/2007 in four shallow wells, two located in irrigated fields and the others in native. The greatest chloride concentration in the soil profiles was registered during rainfall season, suggesting the effect of sea-salt aerosols influence on chloride soil content. The greatest nitrate concentration occurred under irrigation period. Also, the results show that irrigation caused the groundwater concentration of NO3-N to increase from 1.52 to 19.3mgL-1, thereby, exceeding the standards on Regulation MS number 518/2004 and 357/2005 Resolution.

Produção de sedimentos em microbacias hidrográficas semiáridas sobre manejos diferenciados

The aim of this study was to evaluate and compare the sedimentological behavior in two small rural watersheds in the semiarid Northeast of Brazil, examining the influence of human activity on the sediment yields. The studied area is sited in the Alto Jaguaribe basin, more precisely in the Iguatu County, Ceara State. The experimental area was composed of two small watersheds denominated B1 and B2. In watershed B1 a treatment (thinning) was applied, eliminating the plant species with diameters lower than 10 cm. The results showed that the Caatinga clearing practice did have an influence in changing the sediment yield during the first events. It was also found that the magnitude of previous events contributed to an increase in the sediment yields by the subsequent events as a consequence of the sediment deposit in the drainage network. The accumulated sediment yields reached at the end of the 2009 rainfall season values of 1.45 and 1.39 tons ha -1 year -1 for B1 and B2, respectively, with no significant difference at 5%. It was concluded that, even when the effect of treatment on the sediment yields at the beginning of the rainy season is measured, the total sediment yields was not changed by the adoption of clearing. Therefore, it is a management system that can be employed in the land use at semiarid regions.

Respostas hidrológicas em pequenas bacias na região semiárida em função do uso do solo

The main goal of this study was to evaluate and to compare the hydrological behavior of small watersheds investigating the influence of the anthropogenic activities and the hydrologic responses due to these activities. The experimental area was composed of two small watersheds denominated B1 and B2. In watershed B1, a treatment (thinning) was applied, eliminating the species with diameters less than 10 cm. The experimental watershed B2 was not submitted to any treatment maintaing the original vegetation. In this investigation a total of 24 rainfall-runoff events were considered, corresponding to the 2009 rainy season as a whole. The results revealed that the thinning of the caatinga generated modifications in the runoff only in the initial rainy season. The growing of herbaceous vegetation attenuated the water flow and reduced the runoff in B1, promoting small changes in response to the applied treatment. There were, however, higher peak discharges in watershed B1 compared with the preserved watershed.

Runoff curve number for a small forested watershed in a semiarid region of Brazil

Although the Runoff Curve Number method has been developed in the 1950’s, and extensively used worldwide, it has not been so in Brazil, yet. The present study was conducted in a small experimental watershed in the southern central region of Ceara State, Brazil (6°32’S, 39°5’W). The watershed is representative of caatinga, a type of scrubby forest, characteristic of the semiarid northeast in Brazil. The watershed has a mean annual rainfall of 800 mm, being 85% concentrated in the January to May period. All streams are ephemeral, and runoff persists until 24 hours after the causing rainfall event is over. Rainfall and streamflow records (64 rainfall-runoff events) were collected at a station located at the watershed outlet from 2008 to 2011. The representative watershed curve number, was determined by the following methods: a) arithmetic mean; b) geometric mean; c) median and c) asymptotic curve fit. For curve number computation, both unranked and ranked paired rainfall-runoff depth of each event was used. Results showed that the arithmetic mean value of curve number (78.8) is very close to the median value (79.4) and both are larger than the geometric mean (78.0). A smaller value of curve number (76.3), however, was obtained when using the asymptotic approach. The observed curve numbers, ranging from 73.0 to 86, decrease with increasing rainfall depth, and tend to a constant value towards larger rainfall events, which are the events that lead to flooding. The watershed presented a standard response.

Desenvolvimento de equações Intensidade-Duração-Frequência sem dados pluviográficos em regiões semiáridas

Neste estudo foram feitas a validacao da metodologia de desagregacao de chuvas das isozonas e sua utilizacao no desenvolvimento de equacoes IDF (Intensidade-Duracao-Frequencia) para tres municipios da Regiao Metropolitana do Cariri, Ceara, desprovidos de pluviografos. Na validacao utilizaram-se dados de estacoes localizadas em zonas climatologicas distintas da Regiao Metropolitana do Cariri e de uma estacao localizada na mesma zona. As precipitacoes maximas diarias anuais foram ajustadas e testadas pelas distribuicoes de probabilidade de Gumbel, Log-Normal II-P, Log-Normal III-P, Gama II-P e Gama III-P. As intensidades de chuvas estimadas pelo metodo das isozonas apresentaram altos indices de concordância e desempenho de Willmott, quando comparadas com as estimadas pelas respectivas equacoes IDF. As precipitacoes maximas diarias anuais utilizadas na aplicacao do metodo das isozonas se ajustaram, respectivamente, as distribuicoes Gama III, Log-Normal II e Gama II; entretanto, verificou-se que outras funcoes podem ser utilizadas sem perda significativa na precisao das estimativas; esses resultados indicam a viabilidade da utilizacao do metodo das isozonas como alternativa na elaboracao das equacoes IDF em regioes nao monitoradas.