Rainfall over the northeast part of Brazil is highly influenced by several weather systems such as trade winds, the Intertropical Convergence Zone, Easterly Wave Disturbances, Bolivia High and Atlantic Sub-tropical Anticyclone. The objectives of this work were to identify, using cluster analysis, spatial and temporal rainfall patterns for the northeastern Brazilian state of Alagoas, and to relate those patterns with the weather systems that occur over that region, which is the most populated area of semiarid climate in the world. The dataset consists of 30-years long time series of rainfall from 36 stations located on the state. Hierarchical clustering using Ward's algorithm was used to classify the sites into five groups. The stations were grouped according to the distance to the coast and orography. Rainfall is not uniformly distributed in space and time in all regions, such as in two groups within the arid zone, where more than 60% of annual precipitation occurs in a period of 5 months (March to July). Rainfall was highest in the coastal regions and over areas of the state with high altitude, due to orographic rainfall. Overall, rainfall over the state of Alagoas is characterized by strong gradients from the coast to the continent and from north to south due to the physiography of the region and the influence of weather systems with different time scales.

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We evaluated the distribution, percentage, and homogeneous regions of fire foci in Brazil over 1998-2011. Included are numbers of fire foci by regions and states as well as their seasonal and monthly variations, with emphasis on human activities and their relationships with producing systems and rainfall inhibitors. We used data from forest fire meteorological satellites, obtained from the Centro de Previsão do Tempo e Estudos Climáticos. Evaluation of regional fire foci distributions gave 37.15 % for the central west and just 1.75 % in the south. Brazilian regions with the highest densities of forest fires per unit area were the northeast, central west, and north. Lowest densities were in the north, southeast, and south. The states of Mato Grosso, Pará, Maranhão, Bahia, Rondônia, and Tocantins had the greatest numbers of fire foci during our study period. The Federal District and the states of Sergipe, Espírito Santo, Rio de Janeiro, Rio Grande do Norte, and Alagoas had the smallest numbers. Spring (62.2 %) and winter (28.7 %) had higher frequencies than summer (6.7 %) and autumn (2.7 %). A clustering technique showed three homogeneous regions of fire foci in Brazil. The regional grouping technique showed the influence of synoptic systems and large-scale patterns of fires in the country. In addition to the use of NOAA-12 satellite images for monitoring Brazilian fire foci, orbital platforms such as MMODIS-01D and T-AQUA can be used. Finally, anthropogenic activities (deforestation, agriculture, livestock, mining, and industrial) and the variability of meteorological systems affected the fire increase during the study period.

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Resumo -O objetivo deste trabalho foi determinar regiões homogêneas baseadas na sazonalidade da precipitação pluvial mensal e a distribuição de probabilidade que melhor se ajusta à precipitação dessas regiões no Estado de Táchira, Venezuela. Utilizaram-se valores da precipitação mensal de 25 estações climatológicas, que apresentam séries entre 24 e 62 anos. Aplicou-se o método de Ward no agrupamento dos meses com precipitação pluvial mensal similar e também no das localidades com precipitação similar (regiões homogêneas). Avaliaram-se os ajustes das funções de densidade exponencial, gama, Gumbel, normal, log-normal a três parâmetros, e Weibull aos dados observados de precipitação mensal. A variação sazonal da precipitação no Estado de Táchira apresenta três períodos estatisticamente definidos como: seco, transição e úmido. Os períodos seco e úmido apresentam quatro regiões homogêneas de precipitação mensal similar e o de transição três. No período seco, a distribuição de probabilidade recomendada para as estimativas mensais é a exponencial, com exceção da região homogênea com os maiores valores de precipitação pluvial do período, onde a gama se sobressai. No período chuvoso, em todas as regiões homogêneas, a distribuição normal predomina, com exceção de agosto, em que a gama prevalece. Já nos meses de transição, destacam-se as distribuições gama, em abril, e normal, em novembro.Termos para indexação: chuva, funções densidade de probabilidade, análise de agrupamento, Ward. Homogeneous regions and probability density functions of pluvial precipitation in Táchira State, VenezuelaAbstract -The objective of this work was to determine regions of monthly pluvial precipitation based on the seasonal and the probability distribution that best fit to precipitation of those areas in the State of Táchira, Venezuela. Long-term series of 24 throughout 62 years of monthly precipitation data of 25 climatological stations were used. The Ward's clustering methods of analyses was used to group the months with similar monthly pluvial precipitation and also the climatological locations with similar precipitation (homogeneous regions). The adjust of the probability density functions exponential, Gamma, Gumbel, normal, log-normal were evaluated with three parameters as well as Weibull distributions in order to observe monthly precipitation data. The precipitation seasonal variation at the State of Táchira presents three periods statistically defined as: dry, transition, and wet.

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