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Reconstructing cold climate paleoenvironments from micromorphological analysis of relict slope deposits (Serra da Estrela, Central Portugal)
Publication . Nieuwendam, Alexandre; Vieira, Gonçalo; Schaefer, Carlos; Woronko, Barbara; Johansson, Margareta
The paper focuses on analysis of macro- and micromorphological characteristics of
relict slope deposits in Serra da Estrela (Portugal) to understand the significance of
different slope processes and paleoenvironmental settings. Micromorphology is a
useful sedimentology technique allowing significant advances compared to macroscopic
techniques. Results show that different processes are involved in the development
of the slope deposits, reflecting different environmental conditions. The main
processes responsible for the emplacement of the relict slope deposits are solifluction,
debris-flow and runoff, but postdepositional changes are also present. Solifluction
was identified in slope deposits between 650 and 1500 m a.s.l. The common
microfeatures identified are circular arrangement of grains with a core grain, rounded
vesicles, vertical grains, matrix deformations and fine-grained deposits. Slope
deposits above 1300 m a.s.l have a platy microstructure and coincide with the altitudinal
range of the relict rock glaciers, indicating the elevation limit of permafrost.
Below this altitude platy microstructures are less frequent. Slope deposits in northfacing
slopes were affected by frost-induced processes in a seasonal frost regime,
followed by a postdeposition illuvial phase. Debris-flow and runoff were identified in
slope deposits between 680 and 1260 m a.s.l. The common microfeatures are
oblique grains, grain dumps, and coarse and fine grain lineations, and banded microstructures
were identified in runoff processes. Debris-flow deposits have a circular
arrangement of grains without a core grain, identified in sediments in paraglacial and
periglacial environments. The slope deposits show evidence of past periods of
enhanced periglacial activity since the last glaciation until the Younger Dryas.
Regional rainfall thresholds for landslide occurrence using a centenary database
Publication . Vaz, Teresa; Zêzere, José; Pereira, Susana; Oliveira, Sérgio Cruz; Garcia, Ricardo A. C.; Quaresma, Ivânia
This work proposes a comprehensive method to assess rainfall thresholds for landslide initiation using a centenary landslide database associated with a single centenary daily rainfall data set. The method is applied to the Lisbon region and includes the rainfall return period analysis that was used to identify the critical rainfall combination (cumulated rainfall duration) related to each landslide event. The spatial representativeness of the reference rain gauge is evaluated and the rainfall thresholds are assessed and calibrated using the receiver operating characteristic (ROC) metrics.
Results show that landslide events located up to 10 km from the rain gauge can be used to calculate the rainfall thresholds in the study area; however, these thresholds may be used with acceptable confidence up to 50 km from the rain gauge. The rainfall thresholds obtained using linear and potential regression perform well in ROC metrics. However, the intermediate thresholds based on the probability of landslide events established in the zone between the lower-limit threshold and the upper-limit threshold are much more informative as they indicate the probability of landslide event occurrence given rainfall exceeding the threshold. This information can be easily included in landslide early warning systems, especially when combined with the probability of rainfall above each threshold.
Droughts in Portugal in the 18th century: a study based on newly found documentary data
Publication . Fragoso, Marcelo; Carraça, Maria da Graça; Alcoforado, Maria Joao
A renewed interest in historical droughts is due to the current climate change issues
and also to the recent extreme drought of 2017 in Portugal. This work aims to
lengthen the historical drought series and help improve projections for the future.
The main droughts of the 18th century in mainland Portugal were identified using
mostly direct documentary sources: individual (poems, letters, memoirs, manuscripts
and printed newspapers) and institutional (ecclesiastical and administrative),
as well as accounts of Pro pluvia ceremonies and processions. All the records had
been assembled in the KlimHist database (http://clima.ul.pt/Klimhist-project).A summary
statistical analysis of the drought evidence including its impacts was performed
to assess its temporal distribution and geographical incidence. A strong precipitation
variability was detected, which, similar to the present times, hardly presents trends in
long series. The main years of drought during the 18th century in Portugal are
highlighted, particularly the severe and long-lasting 1737–38 and 1753–54 droughts
that, together with their atmospheric causes, were studied in detail. There are more
drought records for Southern Portugal (SP) than for Northern Portugal (NP). It was
also observed that spring March, April and May (MAM) and winter December, January
and February (DJF) drought evidence are more frequent in SP, whereas in NP there
are more records concerning summer June, July and August (JJA). The results obtained
agree with those of others of the Iberian Peninsula (IP). Despite Portugal being a small
country, our results confirm the existence of an important climatic boundary between
the NP and the SP with different precipitation variability.
Vegetation recovery patterns in burned areas assessed with Landsat 8 OLI Imagery and environmental biophysical data
Publication . Meneses, B.M.
Vegetation recovery after the large wildfires that occurred in central Portugal in 2017 is assessed in the present study. These wildfires had catastrophic consequences, among which were human losses and a vast extent of forest devastation. Landsat 8 OLI images were used to obtain the land use and cover (LUC) classification and to determine the Normalized Burned Ratio index (NBR) for different times. NBR results were used to determine the difference between the NBR (dNBR) before the fire (pre-fire) and after the fire (post-fire), and the results obtained were cross-checked with the LUC. The dNBR results were cross-referenced with biophysical data to identify the characteristics of the most important burned areas in need of vegetative recovery. The results showed the spatial differentiation in vegetation recovery, highlighting different factors in this process, in particular the type of vegetation (the predominant species and bank of seeds available), the biophysical characteristics of burned areas (for example, the soil type in burned areas), the continentality gradient, and the climate conditions. The vegetation recovery was differentiated by time according to the species present in the burned areas pre-fire. In general, shrubland recovery was faster than that of tree species, and the recovery was more marked for species that were regenerated by the rhizomes after fire. The recovery process was also influenced by the season in the study area. It was more efficient in the spring and at the beginning of the summer, highlighting the importance of optimal conditions needed for vegetation regeneration, such as the temperature and precipitation (soil humidity and water availability for growing plants). The results of this research are important to forest planning: the definition of the strategies for the ecosystems’ recovery, the adoption of preventive measures to avoid the occurrence of large wildfires, the modification of anthropogenic practices, etc.
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Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
5876
Número da atribuição
UID/GEO/00295/2013