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Universidade de Lisboa (2021)

Vegetation Carbon Losses Linked to Mediterranean Extreme Events

Silva, Tiago Miguel Rivero Ermitão Rodrigues da

Titre : Vegetation Carbon Losses Linked to Mediterranean Extreme Events

Auteur : Silva, Tiago Miguel Rivero Ermitão Rodrigues da

Université de soutenance : Universidade de Lisboa

Grade : Mestrado, Ciências Geofísicas (Meteorologia e Oceanografia) 2021

Résumé
The activity of terrestrial ecosystems is particularly susceptible to the climate variability and, facing the recently global and regional changes, has been responding with rapid changes on natural vegetation cycle, plants productivity and terrestrial carbon uptake. Droughts have been broadly recognized, among a wide range of extreme events, as playing a central role on the carbon cycle. Dry permanent conditions contribute to the occurrence of high hydric stress on vegetation, generating disturbances on the regular photosynthesis, carbon uptake and regular plants mechanisms. Furthermore, they may increase the risk of fires due to the higher vulnerability of ecosystems, enhancing the losses on vegetation productivity, and inhibiting, generally, their regenera-tion process for a long time. Europe, and in particular, the Mediterranean region, has been affected by severe droughts and large fires in the last decades, being an area particularly sensitive to extreme phenomena. Therefore, this work proposes to assess the impact of a set of the severest droughts and large fires, between 2001 and 2019, over three different regions of Mediterranean basin (Iberian Peninsula, Italy and Greece, and France), attempting to analyse their influence on vegetation. It will be assessed the persistence of soil dry conditions and the number of months that the normal activity of vegetation is disturbed. Remote sense products were used to monitor the plant’s productivity, to assess the soil moisture and to detect burned areas. The analysis of soil moisture and primary production of vegetation, for the referred study period, allowed to identify the most hazardous drought events which had larger impacts on ecosystems. Over Iberian Peninsula, both 2005 and 2012 episodes caused wide disturbances on ecosystems, with large areas showing water availability deficit in soils, driving to severe impacts on vegetation and productivity losses of 40 TgC/year. Throughout Italy and Greece region, the events of 2003, 2007 and 2012 affected the ecosystems of about 30-35% of the territory, being 2007 particularly intense due to the combined effect of a drought, major heatwaves and large fires. In France, the 2006 episode affected more than 25% of the vegetation of the territory and induced losses on annual productivity of 25 TgC/year. In turn, the occurrence of severe fire seasons is closely associated with the availability of biomass that easily burns in the presence of an extreme climatic event, such as summer heatwaves (e.g. Iberia in 2003 and 2017, and Italy and Greece in 2007), or persistent droughts in previous months (e.g. Iberia in 2005 and 2012, and Italy and Greece in 2012). The assessment of the disturbances on photosynthetic activity caused by droughts and large fires allowed the quantification of the losses of vegetation productivity, and also, the evaluation of the recov-ery process during the following months. The ecosystems response varies widely, with vegetation may taking months to years to recover the normal activity. The disturbances on net productivity caused by droughts are significantly higher than the ones caused by large fires, especially due to their extension and their timescale, that can last from weeks to several months. However, despite fires have a shorter period of time, these events can strongly inhibit the vegetation to regenerate, amplifying the productivity losses on ecosystems during a long period.

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Page publiée le 15 avril 2022