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- New observations indicate the possible presence of permafrost in North Africa (Djebel Toubkal, High Atlas, Morocco)Publication . Vieira, Goncalo; Mora, Carla; Faleh, AliRelict and present-day periglacial features have been reported in the literature for the upper reaches of the High Atlas mountains, which is the highest range in North Africa (Djebel Toubkal – 4167 m a.s.l.). A lobate feature in the Irhzer Ikhibi south at 3800 m a.s.l. has been previously interpreted as an active rock glacier, but no measurements of ground or air temperatures are known to exist for the area. In order to assess the possible presence of permafrost, we analyse data from June 2015 to June 2016 from two air temperature measurement sites at 2370 and 3210 m a.s.l. and from four ground surface temperature (GST) sites at 3220, 3815, 3980 and 4160 m a.s.l. to characterize conditions along an altitudinal gradient along the Oued Ihghyghaye valley to the summit of the Djebel Toubkal. GSTs were collected at 1 h intervals, and the presence of snow cover at the monitoring sites was validated using Landsat 8 and Sentinel-2 imagery. Two field visits allowed for logger installation and collection and for assessing the geomorphological features in the area. The results show that snow plays a major role on the thermal regime of the shallow ground, inducing important spatial variability. The lowest site at 3220 m had a thermal regime characterized by frequent freeze–thaw cycles during the cold season but with few days of snow. When snow settled, the ground surface remained isothermal at 0 ◦C , indicating the absence of permafrost. The highest sites at 3980 and 4160 m a.s.l. showed very frequent freeze–thaw cycles and a small influence of the snow cover on GST, reflecting the lack of snow accumulation due to the wind-exposed settings on a ridge and on the summit plateau. The site located at 3815 m in the Irhzer Ikhibi south valley had a cold, stable thermal regime with GST varying from −4.5 to −6 ◦C from December to March, under a continuous snow cover. The site’s location in a concave setting favours wind-driven snow accumulation and lower incoming solar radiation due to the shading effect of a ridge, inducing the conservation of a thick snow pack. The stable and low GSTs are interpreted as a strong indicator of the probable presence of permafrost at this site, which is an interpretation supported by the presence of lobate and arcuate features in the talus deposits. We present first results and further observations using geophysics, and borehole measurements are foreseen. This is the first time that probable permafrost has been reported from temperature observations in the mountains of North Africa.
- Evaluation of water resources in a high-mountain basin in Serra da Estrela, central Portugal, using a semi-distributed hydrological modelPublication . Espinha Marques, J.; Samper, J.; Pisani, B.; Alvares, D.; Carvalho, J. M.; Chaminé, H. I.; Marques, J. M.; Vieira, Goncalo; Mora, Carla; Sodré Borges, F.High-mountain basins provide a source of valuable water resources. This paper presents hydrological models for the evaluation of water resources in the highmountain Zeˆzere river basin in Serra da Estrela, Central Portugal. Models are solved with VISUAL BALAN v2.0, a code which performs daily water balances in the root zone, the unsaturated zone and the aquifer and requires a small number of parameters. A lumped hydrological model fails to fit measured stream flows. Its limitations are overcome by considering the dependence of the temperature and precipitation data with elevation and the spatial variability in hydrogeomorphological variables with nine sub-basins of uniform parameters. Model parameters are calibrated by fitting stream flow measurements in the Zeˆzere river. Computed stream flows are highly sensitive to soil thickness, whereas computed groundwater recharge is most sensitive to the interflow and percolation recession coefficients. Interflow is the main component of total runoff, ranging from 41 to 55% of annual precipitation. High interflows are favored by the steep relief of the basin, by the presence of a high permeability soil overlying the fractured low permeability granitic bedrock and by the extensive subhorizontal fracturing at shallow depths. Mean annual groundwater recharge ranges from 11 to 15% of annual precipitation. It has a significant uncertainty due to uncertainties in soil parameters. This methodology proves to be useful to handle the research difficulties regarding a complex mountain basin in a context of data scarcity.
- Environmental conditions and childhood asthma in Lisbon: an exploratory analysis for autumn thunderstormPublication . Canário, Paulo; Fragoso, Marcelo; Mora, Carla; Nogueira, HelenaAsthma attacks triggered by thunderstorms have been described in several countries. The rises in pollen concentrations, attributed to atmospheric electrical discharges, were considered the leading cause of these outbreaks. The presence of various pollutants as well as certain weather conditions may contribute synergistically to the onset of exacerbations in patients with a previous diagnosis of asthma. This study aims to investigate whether atmospheric electrical discharges exert any influence on the number of emergency admissions due to childhood asthma, in autumn, in Lisbon. The investigation will examine whether there are isolated or combined effects of meteorological variables, pollutant and pollen concentrations that favour an increase in the number of exacerbations of asthma symptoms. For this purpose we compared the number of asthma admissions in periods with and without thunderstorms in a Lisbon paediatric emergency service. Increasing pollen concentrations attributed to thunderstorms reported in the literature were not found in Lisbon in the days analysed. There was also an absence of relationship between admissions for asthma and air pollution. Associations between hospitalisations due to asthma crisis and atmospheric variables were documented. In Lisbon, no influence of atmospheric electrical discharges in the variation of the number of emergency admissions due to childhood asthma was verified in the studied period (autumn). On the contrary, it was verified that a decrease in minimum temperature positively reinforces these admissions.
- Accurate determination of surface reference data in digital photographs in ice-free surfaces of Maritime AntarcticaPublication . Pina, Pedro; Vieira, Goncalo; Bandeira, Lourenço; Mora, CarlaThe ice-free areas of Maritime Antarctica show complex mosaics of surface covers, with wide patches of diverse bare soils and rock, together with various vegetation communities dominated by lichens and mosses. The microscale variability is difficult to characterize and quantify, but is essential for ground-truthing and for defining classifiers for large areas using, for example high resolution satellite imagery, or even ultra-high resolution unmanned aerial vehicle (UAV) imagery. The main objective of this paper is to verify the ability and robustness of an automated approach to discriminate the variety of surface types in digital photographs acquired at ground level in ice-free regions of Maritime Antarctica. The proposed method is based on an object-based classification procedure built in two main steps: first, on the automated delineation of homogeneous regions (the objects) of the images through the watershed transform with adequate filtering to avoid an over-segmentation, and second, on labelling each identified object with a supervised decision classifier trained with samples of representative objects of ice-free surface types (bare rock, bare soil, moss and lichen formations). The method is evaluated with images acquired in summer campaigns in Fildes and Barton peninsulas (King George Island, South Shetlands). The best performances for the datasets of the two peninsulas are achieved with a SVM classifier with overall accuracies of about 92% and kappa values around 0.89. The excellent performances allow validating the adequacy of the approach for obtaining accurate surface reference data at the complete pixel scale (sub-metric) of current very high resolution (VHR) satellite images, instead of a common single point sampling.
- Geografia física em regiões de montanha: a Ilha da Madeira e as Serras da Arrábida e da Estrela: homenagem a Orlando RibeiroPublication . Mora, CarlaComemorou-se, em 2011, o 100º aniversário do nascimento de Orlando Ribeiro. Depois de uma reestruturação dos agora denominados Grupos de Investigação do Centro de Estudos Geográficos (CEG), o grupo Zephyrus - “Alterações Climáticas e Sistemas Ambientais”, resolveu divulgar dois textos em memória do Professor Orlando Ribeiro, numa colecção que agora se inicia. Directa ou indirectamente, os autores dos textos aqui editados sofreram influência dos trabalhos, das reflexões e da personalidade de Orlando Ribeiro. No entanto, de entre as pessoas do grupo, fui eu quem mais conviveu com Orlando Ribeiro que, embora não tenha sido meu Professor, orientou o meu trabalho de fim de curso sobre a Arrábida e acompanhou-me em numerosas excursões. A relação de amizade com o “Professor Orlando” e com a “Professora Suzana”, que se foi cimentando ao longo dos anos e que ainda hoje perdura com Suzanne Daveau, foi (e continua a ser) fonte de grande enriquecimento pessoal e intelectual para mim. Nestes dois últimos anos, o nosso grupo foi reorganizado. No início de 2013, faleceu o nosso Colega Henrique Andrade, grande Geógrafo e Amigo dedicado, quando eu tinha acabado de me aposentar. Retirei-me também da liderança do núcleo “Clima e Mudanças Ambientais” (CLIMA), depois de mais de 20 anos de serviço de coordenação dos grupos de Geo-Ecologia e, depois, CliMA do CEG; nessa altura, os investigadores seniores do CliMA, Carlos Neto (com preferência por temas de biogeografia e conservação da natureza), Marcelo Fragoso (climatologia sinóptica e histórica) e António Lopes (climatologia urbana e ordenamento do território) decidiram que este ficaria a liderar o grupo, tarefa que cumpriu com eficácia e generosidade. Na sequência da reestruturação da investigação do CEG no final de 2013, formou-se o Grupo de Investigação Zephyrus, resultante da fusão dos núcleos CLIMA e AntECC (“Ambientes Antárcticos e Alterações Climáticas”, então coordenado por Gonçalo Vieira, um dos pioneiros nacionais da investigação antárctica) [...]
- Frozen ground and snow cover monitoring in the South Shetland Islands, Antarctica: instrumentation, effects on ground thermal behaviour and future researchPublication . De Pablo, M. A.; Ramos, M.; Molina, A.; Vieira, Goncalo; Hidalgo, M. A.; Prieto, M.; Jiménez, J. J.; Fernández, S.; Recondo, C.; Calleja, J. F.; Peón, J. J.; Mora, C.The study of the thermal behavior of permafrost and active layer on the South Shetland Islands, in the western side of the Antarctic Peninsula (Antarctica), has been our research topic since 1991, especially after 2006 when we established different active layer thickness and ground thermal monitoring sites of the CALM and GTN-P international networks of the International Permafrost Association. Along this period, the snow cover thickness did not change at those sites, but since 2010, we observed an elongation on the snow cover duration, with similar snow onset, but a delay on the snow offset. Due to the important effects of snow cover on the ground thermal behavior, we started in late 2015 a new research project (PERMASNOW) focused on the accurate monitoring of the snow cover (duration, density, snow water equivalent and distribution), from very different approaches, including new instrumentation, pictures analysis and remote sensing on optical and radar bands. Also, this interdisciplinary and international research team intends to compare the snow cover and ground thermal behavior with other monitoring sites in the Eastern Antarctic Peninsula where the snow cover is minimum and remains approximately constant.
- Régimen térmico y variabilidad espacial de la capa activa en Isla Decepcion, AntártidaPublication . Vieira, Goncalo; Caselli, Alberto; Mora, Carla; Ramos, Miguel; Pablo, Miguel Angel de; Neves, Mário; Santos, Fernando; Bernardo, Ivo; Gilichinsky, David; Abramov, Andrey; Batista, Vanessa; Melo, Raquel; Nieuwendam, Alexandre; Ferreira, Alice; Oliva, MarcEl programa de monitoreo de capa activa (CALM) fue desarrollado en las últimas décadas con la finalidad de comprender el impacto del cambio climático sobre los ambientes con permafrost. Este trabajo analiza los resultados obtenidos, en los últimos seis años, de los sitios CALM-S Irizar, Cráter Lake y Refugio Chileno, ubicados en Isla Decepción. En ellos se ha medido el espesor, el estado térmico y la distribución espacial de la capa activa. En los sitios Irizar y Refugio Chileno la evolución del espesor de capa activa varió interanualmente sin una clara tendencia dentro del corto período analizado; por el contrario, el sitio Cráter Lake evidenció una tendencia a la disminución de espesor. La distribución espacial como el espesor de dicha capa en los tres sitios de monitoreo, mostraron estar condicionados principalmente por la potencia de la cubierta de nieve, la litología y la exposición a los vientos. El relieve, la topografía de detalle, la orientación de las laderas frente a la radiación solar incidente, ejercieron un control menor sobre esta distribución. El estado térmico de la capa activa evidenció el control ejercido sobre ella de la temperatura del aire y de la cubierta nival. Así bajo reducidos espesores de nieve, el modelo de penetración en profundidad de la isoterma de 0 ºC, ha permitido aproximar satisfactoriamente el espesor de capa activa.
- A proxy for snow cover and winter ground surface cooling: mapping Usnea sp. communities using high resolution remote sensing imagery (Maritime Antarctica)Publication . Vieira, Goncalo; Mora, Carla; Pina, Pedro; Schaefer, Carlos E.R.Usnea sp. formations show a spatial distribution coinciding with wind-exposed locations on rock knobs or sedimentary bodies, while they are commonly absent from concave sites. Field collection of georeferenced ground truthing data in the Meseta Norte (Fildes Peninsula, Maritime Antarctica) and the application of supervised classification techniques over a summer high resolution QuickBird satellite scene showed excellent classification accuracy for the different landcover types. The results show that Usnea formation distribution maps are a viable proxy for areas with less snow during the cold season. Such an approach provides input for permafrost and active layer modelling since snow acts as a critical control on ground surface heat balance. Since snow mapping is extremely difficult in Maritime Antarctica our tested approach provides important added-value for empirical–statistical modelling of permafrost distribution.
- Evaluation of single-band snow-patch mapping using high-resolution microwave remote sensing: an application in the maritime AntarcticPublication . Mora, Carla; Jiménez Cuenca, Juan Javier; Pina, Pedro; Catalão, João; Vieira, GoncaloThe mountainous and ice-free terrains of the maritime Antarctic generate complex mosaics of snow patches, ranging from tens to hundreds of metres. These can only be accurately mapped using high-resolution remote sensing. In this paper we evaluate the application of radar scenes from TerraSAR-X in High Resolution SpotLight mode for mapping snow patches at a test area on Fildes Peninsula (King George Island, South Shetlands). Snow-patch mapping and characterization of snow stratigraphy were conducted at the time of image acquisition on 12 and 13 January 2012. Snow was wet in all studied snow patches, with coarse-grain and rounded crystals showing advanced melting and with frequent ice layers in the snow pack. Two TerraSAR-X scenes in HH and VV polarization modes were analysed, with the former showing the best results when discriminating between wet snow, lake water and bare soil. However, significant overlap in the backscattering signal was found. Average wet-snow backscattering was −18.0 dB in HH mode, with water showing −21.1 dB and bare soil showing −11.9 dB. Single-band pixel-based and object-oriented image classification methods were used to assess the classification potential of TerraSAR-X SpotLight imagery. The best results were obtained with an object-oriented approach using a watershed segmentation with a support vector machine (SVM) classifier, with an overall accuracy of 92 % and Kappa of 0.88. The main limitation was the west to north-west facing snow patches, which showed significant error, an issue related to artefacts from the geometry of satellite imagery acquisition. The results show that TerraSAR-X in SpotLight mode provides high-quality imagery for mapping wet snow and snowmelt in the maritime Antarctic. The classification procedure that we propose is a simple method and a first step to an implementation in operational mode if a good digital elevation model is available.
- Permafrost conditions in the Mediterranean region since the Last GlaciationPublication . Oliva, Marc; Žebre, M.; Guglielmin, M.; Hughes, P.D.; Çiner, A.; Vieira, Gonçalo; Bodin, X.; Andrés, N.; Colucci, R.R.; García-Hernández, C.; Mora, Carla; Nofre, J.; Palacios, D.; Pérez-Alberti, A.; Ribolini, A.; Ruiz-Fernández, J.; Sarıkaya, M.A.; Serrano, E.; Urdea, P.; Valcárcel, M.; Woodward, J.C.; Yıldırım, C.The relatively warm climate conditions prevailing today in the Mediterranean region limit cold geomorphological processes only to the highest mountain environments. However, climate variability during the Late Pleistocene and Holocene has led to significant spatio-temporal variations of the glacial and periglacial domain in these mountains, including permafrost conditions. Here, we examine the distribution and evolution of permafrost in the Mediterranean region considering five time periods: Last Glaciation, deglaciation, Holocene, Little Ice Age (LIA) and present-day. The distribution of inactive permafrost-derived features as well as sedimentary records indicates that the elevation limit of permafrost during the Last Glaciation was between 1000 m and even 2000 m lower than present. Permafrost was also widespread in non-glaciated slopes above the snowline forming rock glaciers and block streams, as well as meter-sized stone circles in relatively flat summit areas. As in most of the Northern Hemisphere, the onset of deglaciation in the Mediterranean region started around 19-20 ka. The ice-free terrain left by retreating glaciers was subject to paraglacial activity and intense periglacial processes under permafrost conditions. Many rock glaciers, protalus lobes and block streams formed in these recently deglaciated environments, though most of them became gradually inactive as temperatures kept rising, especially those at lower altitudes. Following the Younger Dryas glacial advance, the Early Holocene saw the last massive deglaciation in Mediterranean mountains accompanied by a progressive shift of permafrost conditions to higher elevations. It is unlikely that air temperatures recorded in Mediterranean mountains during the Holocene favoured the existence of widespread permafrost regimes, with the only exception of the highest massifs exceeding 2500-3000 m. LIA colder climate promoted a minor glacial advance and the spatial expansion of permafrost, with the development of new protalus lobes and rock glaciers in the highest massifs. Finally, post-LIA warming has led to glacial retreat/disappearance, enhanced paraglacial activity, shift of periglacial processes to higher elevations, degradation of alpine permafrost along with geoecological changes.