Abstract
Abstract. In the last decade, Europe has been stricken by two outstanding heatwaves, the 2003 event in western Europe and the 2010 episode over Russia. Both events were characterized by record-breaking temperatures and widespread socio-economic impacts, including significant increments on human mortality, decreases in crop yields and in hydroelectric production. Previous works have shown that an extreme climatic event does not always imply an extreme response by ecosystems. This work attempts to assess how extreme was the vegetation response to the heatwaves during 2003 and 2010 in Europe, in order to quantify the impacts of the two events on carbon fluxes in plant productivity and to identify the physical drivers of the observed response. Heatwave impacts in vegetation productivity were analysed using MODIS products from 2000 to 2011. Both 2003 and 2010 events led to marked decreases in plant productivity, well below the climatological range of variability, with carbon uptake by vegetation during August reaching negative anomalies of more than 2 standard deviations, although the 2010 event affected a much larger extent. A differentiated response in autotrophic respiration was observed, depending on land-cover types, with forests increasing respiration rates in response to the heatwaves, while in crops respiration rates decreased. The widespread decrease in carbon uptake matched the regions where very high temperature values were also preceded by a long period of below-average precipitation, leading to strong soil moisture deficits. In the case of the 2003 heatwave, results indicate that moisture deficits coupled with high temperatures drove the extreme response of vegetation, while for the 2010 event very high temperatures appear to be the sole driver of very low productivity.
Highlights
Heatwaves in Europe are expected to become more frequent, intense and long lasting, mostly due to the increase in mean summer temperature and corresponding variability (Luterbacher et al, 2004; Meehl and Tebaldi, 2004; Fischer and Schär, 2010)
Spectral observations of the fraction of absorbed photosynthetically active radiation were used to assess the robustness of the results found in gross primary productivity (GPP), net primary productivity (NPP) and PsN patterns
The separate analysis of the eastern and western sectors shows that these very low NPP values at the European scale were due to strong anomalies in western Europe in 2003 and in the eastern sector in 2010, coinciding with the main regions affected by the heatwaves in each year
Summary
Heatwaves in Europe are expected to become more frequent, intense and long lasting, mostly due to the increase in mean summer temperature and corresponding variability (Luterbacher et al, 2004; Meehl and Tebaldi, 2004; Fischer and Schär, 2010). Bastos et al.: Impacts of 2003 and 2010 heatwaves in plant productivity far more intense than the 2003 event, with a record-breaking area of ∼ 2 million km compared with ∼ 1 million km in central Europe in 2003 These heatwaves were responsible for a significant increase of human mortality, unusually large fires and widespread impacts in ecosystems and crop yields (Trigo et al, 2005; García-Herrera et al, 2010; Barriopedro et al, 2011). Several works have stressed the role of land–atmosphere coupling, soil-moisture feedbacks, in climate variability and extremes in Europe (Seneviratne et al, 2006; Hirschi et al, 2011) Both 2003 and 2010 heatwaves were associated with persistent anti-cyclonic conditions from late spring to summer and with precipitation deficits from late winter until August. This work follows the methodology proposed by Smith (2011) and performs a comparative analysis of the 2003 and 2010 heatwaves to (i) quantify the impact of the mega-heatwaves on plant carbon uptake (ii) assess how exceptional the response of vegetation to both events was (iii) identify the physical drivers of vegetation dynamics
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