Rafaela Silveira Rodrigues Almeida

Shannon information entropy for assessing space-time variability of rainfall and streamflow in semiarid region.

The principle of maximum entropy can provide consistent basis to analyze water resources and geophysical processes in general. In this paper, we propose to assess the space-time variability of rainfall and streamflow in northeastern region of Brazil using the Shannon entropy. Mean values of marginal and relative entropies were computed for a 10-year period from 189 stations in the study area and entropy maps were then constructed for delineating annual and seasonal characteristics of rainfall and streamflow. The Mann-Kendall test was used to evaluate the long-term trend in marginal entropy as well as relative entropy for two sample stations. High degree of similarity was found between rainfall and streamflow, particularly during dry season. Both rainfall and streamflow variability can satisfactorily be obtained in terms of marginal entropy as a comprehensive measure of the regional uncertainty of these hydrological events. The Shannon entropy produced spatial patterns which led to a better understanding of rainfall and streamflow characteristics throughout the northeastern region of Brazil. The total relative entropy indicated that rainfall and streamflow carried the same information content at annual and rainy season time scales.

Estudo da variabilidade anual e intra-anual da precipitação na região Nordeste do Brasil

This study analyzed rainfall and number of rainy days time series over northeastern region of Brazil with the aim of identifying areas that are more vulnerable to long periods of droughts. The data used in this study were obtained from the National Water Agency (ANA) and Superintendencia do Desenvolvimento do Nordeste (SUDENE) for the period from 1935 to 2000. The variation coefficient and rainy days maps were provided for dry, wet and annual periods of the rainfall and number of rainy days. The results showed that the semiarid region have a higher variation coefficient for both rainfall and rainy days than those located at east coast, tropical thorn forest and northwest of northeastern Brazil. The highest values of the variation coefficient are associated to the lowest values of rainfall and rainy days. The rainfall variability in northeastern Brazil is higher during dry season than rainy season. The high variability in rainfall and rainy days are limiting factors to the rainfed agriculture in semiarid environments.

Entropy theory for analysing water resources in northeastern region of Brazil

ABSTRACT Using the Shannon entropy, the space–time variability of rainfall and streamflow was assessed for daily rainfall and streamflow data for a 10-year period from 189 stations in the northeastern region of Brazil. Mean values of marginal entropy were computed for all observation stations and entropy maps were then constructed for delineating annual and seasonal characteristics of rainfall and streamflow. The Mann-Kendall test was used to evaluate the long-term trend in marginal entropy as well as relative entropy for two sample stations. The marginal entropy values of rainfall and streamflow were higher for locations and periods with the highest amounts of rainfall. The entropy values were higher where rainfall was higher. This was because the probability distributions of rainfall and the resulting streamflow were more uniform and less skewed. The Shannon entropy produced spatial patterns which led to a better understanding of rainfall and streamflow characteristics throughout the northeastern region of Brazil. The total relative entropy indicated that rainfall and streamflow carried the same information content at annual and rainy season time scales.

An analysis of rainfall based on entropy theory

The principle of maximum entropy can provide consistent basis for analyzing rainfall and for geophysical processes in general. The daily rainfall data was assessed using the Shannon entropy for a 10-years period from 189 stations in the northeastern region of Brazil. Mean values of marginal entropy were computed for all observation stations and isoentropy maps were then constructed for delineating annual and seasonal characteristics of rainfall. The Mann-Kendall test was used to evaluate the long-term trend in marginal entropy for two sample stations. The marginal entropy values of rainfall were higher for locations and periods with highest amount of rainfall. The results also showed that the marginal entropy decreased exponentially with increasing coefficient of variation. The Shannon theory produced spatial patterns which led to a better understanding of rainfall characteristics throughout the northeastern region of Brazil. Trend analysis indicated that most time series did not have any significant trends.

General aspects of the climate in the Cabo verde archipelago

O clima das ilhas do arquipelago de Cabo Verde sempre impos muitas restricoes ao desenvolvimento da atividade agricola, devido a um regime pluviometrico com baixos volumes e concentrado numa unica estacao, chamada estacao das aguas (agosto - outubro). O presente estudo utiliza as metodologias apresentadas por Thornthwaite e o sistema de classificacao de Koppen para avaliar e caracterizar o clima no arquipelago de Cabo Verde. Foram utilizadas series temporais mensais de precipitacao e de temperatura do ar mais longa possivel e disponivel para as diversas ilhas, que variaram entre 20 e 30 anos de dados. Para as localidades que existem dados de precipitacao e nao dispunham de dados de temperatura, elas foram estimadas com base no modelo em funcao das coordenadas geograficas. Os resultados do trabalho permitiram concluir que o periodo chuvoso de Cabo Verde coincide com o periodo mais quente do arquipelago. Alem disso, o clima do arquipelago varia de semiarido a arido, exceto a ilha do Fogo que apresenta algumas areas com clima sub umido. O clima desse arquipelago tambem pode ser classificado, de forma geral, como seco desertico muito quente com chuva de inverno e irregulares pela classificacao de Koppen. Abstract The climate on islands of Cape Verde has always imposed many restrictions on agricultural development due to low rainfall regime mainly concentrated in a single season, called of rainy season (August-October). This study used the methodologies presented by Thornthwaite and the Koppen classification for evaluating and to characterize the climate in the Cape Verde archipelago. It was used time series of both monthly rainfall and air temperature as long as possible as well as available to the various islands on the archipelago, ranging between 20 and 30 years. For locations with rainfall data but no air temperature data, air temperature were estimated based on the model as a function of geographic coordinates. The results indicate that the rainy season in Cape Verde coincides with the hottest period on the archipelago, due to convective effects. Moreover, the climate on the archipelago ranges from arid to semiarid, except in the island of Fogo, which presents some areas with sub humid climate according to the Thornthwaite classification. In general form, the climate on the archipelago can also be classified as hot and dry deserts with irregular winter rainfall according to climate classification of Koppen.

An integrated approach based on water, ecological and carbon footprint for tracking human pressure on the planet

Modelos de pegadas de carbono ecologicos e de agua estao sendo cada vez mais usado para monitorar uso pessoal e domestico dos recursos naturais. As pegadas humanas sao uma seria ameaca global e cada nacao esta olhando para as opcoes possiveis para reduzi-las pois suas consequencias sao alarmantes. Este trabalho propoe uma pegada integrada como ferramenta para avaliar os impactos ambientais diretos e indiretos da atividade humana. Com base nas definicoes das pegadas de carbono, hidrica e ecologica, um modelo empirico foi construido para a avaliacao dos impactos ambientais da producao e consumo. Neste trabalho, foi definido, pela primeira vez, o termo “pegada ambiental” como um conjunto de indicadores para acompanhar a pressao humana sobre o planeta sob ângulos diferentes, constituindo-se, assim, o Indice de Sustentabilidade Ambiental Multidimensional (ISAM). Esse indice foi construido na premissa de que nenhum indicador, por si so, e capaz de monitorar de forma abrangente o impacto humano sobre o meio ambiente; os indicadores precisam ser usados e interpretados em conjunto. Semelhancas e diferencas entre os tres indicadores sao, entao, destaque para mostrar como esses indicadores se sobrepoem, interagem e se complementam. A revisao conclui que a “pegada ambiental” e adequada para avaliar sustentabilidade. Abstract Carbon, ecological and water footprints models are increasingly being used for monitoring personal and domestic use of natural resources. These human footprints are a serious global threat and every nation is looking at the possible options to reduce it since its consequences are alarming. This work proposes an integrated footprint as a tool for assessing the direct and indirect environmental impacts from human activity. Based on the definition of carbon, water and ecological footprints, an empirical model was built for the assessment of the environmental impacts of production and consumption. In this work the term “environmental footprint” was first defined as a set of indicators to track human pressure on the planet from different angles, constituting, therefore, the Environmental Sustainability Index Multidimensional (ISAM). This index is built on the premise that no indicator by itself is able to comprehensively monitor human impact on the environment, but indicators must be used and interpreted together. Similarities and differences among the three indicators are then highlighted to show how these indicators overlap, interact, and complement each other. The review concludes that “footprint environmental” is appropriate to assess sustainability.

Aboveground Biomass Dynamics in the Amazonian Rainforest under Influence of Reduction in Rainfall

Exchange of biomass between the ecosystem and the atmosphere plays an important role in regional and global carbon cycles that have a major impact on biodiversity. This study evaluated the effect of reduction in rainfall on the aboveground biomass in an Amazonian rainforest. Data for this study were obtained from the “Long-term drought impact on water and carbon dioxide fluxes in Amazonian Tropical Rainforest Experiment (ESECAFLOR)” which was a subproject of Large Scale Biosphere Atmosphere Experiment in Amazon forest (LBA), carried out in terra firma rainforest in Caxiuana National Forest, Para, Brazil. The experimental design entailed two experimental sites each with one hectare of natural forest: control TFE (a simulated soil drought or ‘throughfall exclusion’ experiment) under normal conditions of climate and treatment TFE with rainfall exclusion of about 50%. The tree growth parameters employed in the study were based on monthly data from the experimental period from January 2005 to May 2009. Results indicated that a decrease in rainfall significantly affected the tree growth parameters, resulting in a decrease of biomass (21.1 t ha-1 year-1) and basal area (1.04 m2 ha-1 year-1). The Amazonian rainforest may become increasingly vulnerable to higher background tree mortality rates in response to drought events, such as El Nino.

Sensible and Latent Heat Storage Fluxes within the Canopy Air-Space in the Amazon Rainforest

Ecosystem–atmosphere exchanges of energy display considerable variability over a range of temporal and spatial scales. This study evaluated the seasonal and annual variations in sensible and latent heat storage fluxes within the canopy air-space in the Amazon rainforest. The data for this study were obtained from the “Long-term drought impact on water and carbon dioxide fluxes in Amazonian Tropical Rainforest Experiment (ESECAFLOR)” which is a subproject of Large Scale Biosphere Atmosphere Experiment in Amazon forest (LBA), carried out in terra firma rainforest in Caxiuana National Forest, Para, Brazil. The data sets also included observations to obtain the sensible and latent heat storage fluxes within forest collected throughout the 1-year period. The vapor pressure and air temperatures were obtained for each 8 m interval from the surface to 32 m. Results indicated that the cumulative sensible heat storage flux in the Amazon rainforest canopy was 167.9 Wm-2 in 2008 and the average daily magnitude was always low for the same period. The latent heat storage flux (ranging from -32.7 to -10 Wm-2) was more influenced by rainfall producing high humidity.