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Southern Portugal experiences the lowest amounts of annual precipitation and the highest level of susceptibility to soil erosion, drought events and desertification phenomena in mainland Portugal. The first goal of this paper was to analyse spatial variability and trends in annual precipitation and erosivity in southern mainland Portugal for the period 1950/1951-2007/2008. The second objective was to evaluate seasonality in relation to precipitation distribution, erosivity and concentration over the same period and to evaluate and detect possible changes in the time trend for precipitation erosivity. In order to achieve these objectives, the annual and seasonal precipitation figures, corresponding to data from 90 rain gauges, were analysed and the Modified Fournier Index and Precipitation Concentration Index calculated for each station. The results obtained revealed distinct behaviour patterns for yearly precipitation, erosivity and concentration trends. Decreases in annual precipitation and erosivity figures accompanied by increases in precipitation concentration were found. Nevertheless, no generalised significant trends have been detected for these variables. In seasonal terms, there was a general trend towards an increase in amount, concentration and precipitation erosivity in autumn and summer, and a significantly reducing in winter. The increase in precipitation erosivity, particularly in the autumn, the most water-erosive season, suggests a rising in potential soil erosion risk in southern Portugal.

Fire scar detection through orbital data can be done using specific techniques, such as the use of spectral indices like the normalized burn ratio (NBR), which are designed to help identify burnt areas as they have typical spectral responses. This paper aims to characterize burn severity and regrowth in areas hit by three fires in the Chapada Diamantina National Park (Bahia, Brazil) and its surrounding area through the differenced normalized burn ratio (dNBR) and relative differenced normalized burn ratio (RdNBR) spectral indices. The data acquired were pretreated and prepared adequately to calculate the indices. We conclude that for the study area, considering the limitations of fieldwork, the multitemporal index dNBR and the relative index RdNBR are important tools for classifying burnt areas and can be used to assess the regrowth of vegetation.

Fires are an important land use tool, a growing global hazard, and a factor involved in landscape processes with feedbacks on land degradation, especially in the Southwestern Mediterranean Europe, where the importance of fires in shaping ecological processes has long been recognized. As fires become recurrent, their intensity and dimension have increased and they have taken on catastrophic proportions, losing their role as catalysts of ecosystem renewal. Fires, and especially large forest fires (LFF), are the main drivers of land degradation in forest areas in Mediterranean sub-humid regions and are likely to increase as a result of climate and other global changes. The study area consists of the whole of mainland Portugal, which for the purpose of civil protection, is divided into 18 districts. The data used, including physical and demographic characteristics, change in land use and land cover, and economic structures are provided mainly by the Institute for the Conservation of Nature and Forests in statistical format and in shapefile format. Throughout the years, LFF in Portugal have become increasingly important. Although LFF in mainland Portugal represent a small fraction of the total occurrences (0.8 %), in accordance with the trends of the Mediterranean Basin, they are responsible for a large percentage of burned areas ([70 %). With the use of the GIS software, we were able to use the available information to generate a map of forest fire recurrences and, with the purpose of detecting homogeneous groups between the districts of mainland Portugal, a cluster analysis was applied. Using a multiple regression analysis, we present the LFF and their recurrence in mainland Portugal at the district level, demonstrating their regional incidence and the similarity between districts.

Ao longo dos últimos anos, Portugal não tem conseguido travar os incêndios florestais, tanto no que diz respeito número de ocorrências como no que se refere à dimensão das áreas ardidas, sobretudo durante o período estival, quando dominam temperaturas elevadas e a dessecação dos combustíveis gera um ambiente propício à propagação dos incêndios, cuja ignição, em mais de 90% dos casos, tem origem em atos humanos, negligentes e intencionais.Com o objetivo de melhor compreender a origem destes incêndios florestais, o presente estudo visa analisar as causas responsáveis pela ignição dos incêndios florestais em Portugal e acompanhar o modo como elas foram evoluindo, quer ao longo do tempo, quer em termos da sua distribuição espacial, no período compreendido entre 1996 e 2010.

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