Terrestrial ecosystems

Climate extremes impacts on terrestrial vegetation

The terrestrial biosphere is a key component of the carbon cycle, taking up about one third of anthropogenic CO2 emissions from the atmosphere. In the future, however, the increasing occurrence of climatic extremes could significantly decrease the efficiency of this land carbon sink. Within the framework of the Belspo SAT-EX project, we investigate how vegetation extremes (e.g. forest dieback, vegetation greening or browning) are driven by climatic extremes (e.g. heatwaves, droughts, heavy precipitation) and how they change in frequency and intensity over the satellite era (approx. 1980-2010).

To achieve this objective, we developed a methodology to identify extreme events in parameters expressing the vegetation activity (e.g. NDVI, LAI, GPP) derived from satellite data and, in parallel, identify extreme events in climate variables that are critical for vegetation growth (precipitation, radiation, and temperature). This research aims to (a) better understand and attribute observed extremes in vegetation to their climatic drivers, and (b) assess the capability of current dynamic vegetation models (DGVMs) to simulate extremes in vegetation.
Relevant project(s): SAT-EX

People involved: Christel van Eck, Catherine Morfopoulos, Pierre Regnier

Terrestrial carbon fluxes to aquatic systems

Lateral transfer of carbon (C) from terrestrial ecosystems into the inland water network is an important component of the global C cycle, which sustains a large aquatic CO2 evasion flux fuelled by the decomposition of allochthonous C inputs. Globally, estimates of the total C exports through the terrestrial–aquatic interface range from 1.5 to 2.7 Pg C yr−1, i.e. of the order of 2–5 % of the terrestrial NPP. Earth system models (ESMs) of the climate system ignore these lateral transfers of C, and thus likely overestimate the terrestrial C sink.
Within the framework of the C-CASCADES and VERIFY projects, we have developed a novel land surface scheme of an ESM (ORCHILEAK) that represents inland waters as biogeochemical reactors interconnected with terrestrial ecosystems and wetlands through lateral exchanges of water, energy, sediments and carbon. This new model, in combination with observational data for calibration and validation, is used to quantify (1) the present-day terrestrial carbon fluxes from the terrestrial biosphere to aquatic systems; (2) the inland water CO2 emissions at regional (Amazon, Europe) and global-scales, and (3) the evolution of these fluxes over the historical period and in the future.
Relevant project(s): C-CASCADES, VERIFY

People involved: Céline Gommet, Ronny Lauerwald, Pierre Regnier

Left : Fluxes of terrestrial-derived carbon into the river network of the Amazon basin, as simulated by the ORCHILEAK model .

Right : Spatial pattern of river-floodplain CO2 evasion (modified from Lauerwald et al., GMD, 2017).