Exceptionally extreme drought in Madeira Archipelago in 2012: Vegetation impacts and driving conditions
Introduction
During the 2011–2012 winter the Iberian Peninsula (IP) was hit in by one of the most severe drought events ever recorded in this region with major socioeconomic and environmental impacts (Trigo et al., 2013). This event allowed quantifying the impact of the synergistic effects of an extreme drought and plant invasion on the water balance of a natural open woody ecosystem in southern Iberia (Caldeira et al., 2015). At a larger scale, this winter was anomalously dry in southern Europe and warmer than usual in northern Europe (Santos et al., 2013). This widespread event also affected the subtropical north-eastern Atlantic islands, in particular the Madeira and Canary Archipelagos, with important adverse impacts on tourism and populations, including the occurrence of unusual fires (Fig. 1; Scott, 2013) in protected natural environment parks.
Madeira is a volcanic Portuguese archipelago in the North Atlantic (NA) (Fig. 2a), with two main islands (Madeira and Porto Santo, Fig. 2b). Madeira Archipelago (MA) is part of the Macaronesian region – the collective name for the Atlantic archipelagos of the Azores, Madeira, the Savage Islands, the Canary Islands and the Republic of Cape Verde – which is an important transitional climatic zone that encompasses a large part of the eastern NA. A description of the Macaronesian weather and climate is presented by Cropper (2013). Madeira Island is located at approximately 900 km southwest of mainland Portugal and roughly 400 km north of the Spanish archipelago of the Canary Islands. According to the Köppen classification, the climate of Madeira Island is classified as temperate with dry and warm summers (Csa) while Porto Santo Island is classified as hot steppe (BSk). Being an east-west oriented mountainous island, precipitation in Madeira is strongly influenced by orographically-generated rainfall. In summary, MA is characterised by a subtropical climate with small temperature range between winters and summers, thus climatic characteristics which are significantly different from southern Europe and the IP, dominated by semiarid climates.
Attractiveness of these islands is closely linked to its warm temperatures throughout the year, luxurious vegetation and natural landscape. The devastating fires in Madeira and Canary Islands in 2012 summer have irreversibly changed the lives of many people who have been forced to abandon their homes and livelihoods (UNESCO, 2012). In July 2012, the media reported that on the Spanish island of Tenerife a violent forest fire reached the edge of the Teide National Park, a major touristic park on the Teide volcano − Spain's highest peak and a UNESCO world heritage site. Emergency services had to evacuate 50 villagers from their homes overnight, and the fire has spread over 1100 ha (2700 acres). On the same week forest fires occurred across the Portuguese island of Madeira for more than two days, forcing dozens of people to abandon their homes. In August 2012, on La Gomera, a holiday destination in Spain's Canary Islands and a biosphere reserve, a forest fire forced the evacuation of nearly 1000 people by ferry overnight. This fire which has spread with high winds and tinder-dry vegetation has destroyed part of a nature reserve. These catastrophic fires represent unusual extreme weather-driven events in these islands of the Macaronesia region. These high impact events motivated this study on the dynamics of the setting and intensification of the outstanding 2011–2012 drought in MA and its associated impacts.
These considerations have motivated the current analysis which has the following complementary goals. Firstly, this work allows evaluating the extreme event from a longer term perspective through the long-term series (150 years) available for Funchal. Moreover, characterizing the extremeness of the drought in this Atlantic Island has never been performed before. Even though the year analysed is similar to the drought episode evaluated by Trigo et al. (2013) for IP, to the best of our knowledge our work presents the first drought assessment for this Atlantic Island using different datasets (meteorological and satellite data). Secondly, the long-term evolution of droughts in Madeira is here compared with those observed in the case of Iberia (Trigo et al., 2013, Vicente-Serrano et al., 2014), in terms of drought indices. Additionally, the ability of a relative simple vegetation index, such as NDVI, to monitor the temporal and spatial variability of vegetation behaviour and drought impacts in Madeira is shown. Finally, we characterize the large scale atmospheric conditions that favoured such extreme drought event in Madeira Archipelago.
Section snippets
Data and methods
A number of different datasets are used in this study including long-term daily precipitation and temperature data from weather stations and reanalysis data to characterise the drought event over MA and the large and synoptic scale dynamics associated with the event. Additionally two remote sensing products are used with the aim of characterizing the impact of the drought in vegetation health and fires’ location.
Was the winter of 2011–2012 the driest in 150 years in Madeira?
Monthly precipitation data (Table 1 and Fig. 2b) presented previously have been used to characterize the dryness and the drought occurrence in the MA. The chosen meteorological stations have different operational periods, spanning between the long continuous precipitation records since 1865 in Funchal to a shorter period since 1961 in Bica da Cana, Santo da Serra and Lugar de Baixo. Fig. 3 shows the accumulated monthly precipitation (AMP) for the 5 most extreme dry hydrological years (October
Conclusions
The use of precipitation records from six meteorological stations, one of them with long-term data measured since 1865, allowed to put into a longer temporal context the observed level of precipitation shortage in Madeira Archipelago. The exceptional dryness of the 2012 drought episode, particularly during the winter season (December to March), confirmed the 2012 winter as the driest in 150 years in Funchal. By means of the SPI the 2012 drought has been classified as extreme – SPI6 lower than
Acknowledgements
This work was supported by the Portuguese Science Foundation (FCT) through project QSECA (PTDC/AAG-GLO/4155/2012). A. M. Ramos and A. Russo were also supported by FCT postdoctoral grants (respectively FCT/DFRH/SFRH/BPD/84328/2012 and FCT/DFRH/SFRH/BPD/99757/2014) and P. M. Sousa was supported by a FCT doctoral grant (SFRH/BD/84395/2012).
The NDVI dataset and the hotspots were kindly supplied respectively by VITO database (http://free.vgt.vito.be) and by Fire Information for Resource Management
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