Biosphere plays an important role in the climate system, controlling the carbon cycle. The activity of ecosystems is in turn particularly sensitive to climate variability [33,47]. The recent regional changes observed in temperature and precipitation seem to have caused an increase in global Net Primary Productivity (NPP), also increasing CO2 fixation by ecosystems [34]. Extreme HDE such as intense heat waves [3,5] and severe droughts [8,35] introduce disturbances in to the dynamics of ecosystems, through high water stress on vegetation, leading to changes in vegetation cycle with significant reductions in crops productivities and growth rates of forests [7,36,37].

Conversely, the responses of the ecosystem can exceed the duration of the climate impacts due the lagged effects on the carbon cycle [16]. There are large uncertainties about the long-term effect of high temperatures on crop growth and the associated carbon cycle. Large amount of above-ground biomass in croplands is removed during harvest. Moreover, he harvest index is also affected by extreme high temperature, increasing the uncertainty about the net effect of HE [48].

Forests present high susceptibility to HDE, namely due to the i) long lifespan of individual organisms that store carbon, ii) high sensitivity to diverse HDE at multiple spatiotemporal scales and iii) high vulnerability of carbon stocks and iv) long recovery time to re-gain previous stocks following HDE.
Fires play an important role in Mediterranean regions, where the vegetation is well adapted to fire regimes [19], being their carbon emissions one of the most uncertain components of the global carbon cycle.

Task 4 will focus on the need to enhance the knowledge about HDE impacts on vegetation dynamics and the carbon cycle. Vegetation parameters available from the LSA-SAF (FVC, LAI, FAPAR and GPP) and the NPP MODIS datasets will be used with the aim to assess HDE direct and indirect contribution to the carbon balance in the short and medium/long term.

Task 4 aims to (1) develop a conceptual framework based on the integration of direct and indirect effects HDE can have on the carbon cycle and to identify the main mechanisms underlying these effects, (2) synthesize how different types of ecosystems are affected by HDE, (3) provide an overview of likely responses of the terrestrial carbon cycle in relation to likely future HDE, and the specific role of lagged impacts and (4) assess the usefulness of using the datasets of biomass accumulation (GPP and NPP) in ARM/FRM.