Articles | Volume 11, issue 22
Biogeosciences, 11, 6357–6375, 2014

Special issue: Climate extremes and biogeochemical cycles in the terrestrial...

Biogeosciences, 11, 6357–6375, 2014

Research article 26 Nov 2014

Research article | 26 Nov 2014

Impact of droughts on the carbon cycle in European vegetation: a probabilistic risk analysis using six vegetation models

M. Van Oijen1,2, J. Balkovi3, C. Beer4,5, D. R. Cameron1, P. Ciais6, W. Cramer7, T. Kato6,13, M. Kuhnert8, R. Martin9, R. Myneni10, A. Rammig11, S. Rolinski11, J.-F. Soussana9, K. Thonicke11, M. Van der Velde2, and L. Xu10,12 M. Van Oijen et al.
  • 1Centre for Ecology & Hydrology, Edinburgh, EH26 0QB, UK
  • 2Bioforsk, Saerheim, Norway
  • 3International Institute for Applied Systems Analysis (IIASA), Schlossplatz 1, 2361 Laxenburg, Austria
  • 4Max-Planck-Institute for Biogeochemistry, Jena, Germany
  • 5Department of Applied Environmental Science (ITM), Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden
  • 6Laboratoire des Sciences du Climat et de l'Environnement, CEA-CNRS-UVSQ, 91198 Gif-sur-Yvette, France
  • 7Institut Méditerranéen de Biodiversité et d'Ecologie marine et continentale (IMBE), Aix Marseille Université, CNRS, IRD, Avignon Université, 13545 Aix-en-Provence, France
  • 8University of Aberdeen, School of Biological Sciences, Aberdeen, UK
  • 9INRA, Grassland Ecosystem Research, (UR 874), 63100 Clermont-Ferrand, France
  • 10Department of Earth and Environment, Boston University, Boston, USA
  • 11Potsdam Institute for Climate Impact Research (PIK), Telegrafenberg 31, 14473 Potsdam, Germany
  • 12Institute of the Environment and Sustainability (IoES), University of California, Los Angeles, USA
  • 13Research Faculty of Agriculture, Hokkaido University, Sapporo, 060-8589 Japan

Abstract. We analyse how climate change may alter risks posed by droughts to carbon fluxes in European ecosystems. The approach follows a recently proposed framework for risk analysis based on probability theory. In this approach, risk is quantified as the product of hazard probability and ecosystem vulnerability. The probability of a drought hazard is calculated here from the Standardized Precipitation–Evapotranspiration Index (SPEI). Vulnerability is calculated from the response to drought simulated by process-based vegetation models.

We use six different models: three for generic vegetation (JSBACH, LPJmL, ORCHIDEE) and three for specific ecosystems (Scots pine forests: BASFOR; winter wheat fields: EPIC; grasslands: PASIM). The periods 1971–2000 and 2071–2100 are compared. Climate data are based on gridded observations and on output from the regional climate model REMO using the SRES A1B scenario. The risk analysis is carried out for ~ 18 000 grid cells of 0.25 × 0.25° across Europe. For each grid cell, drought vulnerability and risk are quantified for five seasonal variables: net primary and ecosystem productivity (NPP, NEP), heterotrophic respiration (Rh), soil water content and evapotranspiration.

In this analysis, climate change leads to increased drought risks for net primary productivity in the Mediterranean area: five of the models estimate that risk will exceed 15%. The risks increase mainly because of greater drought probability; ecosystem vulnerability will increase to a lesser extent. Because NPP will be affected more than Rh, future carbon sequestration (NEP) will also be at risk predominantly in southern Europe, with risks exceeding 0.25 g C m−2 d−1 according to most models, amounting to reductions in carbon sequestration of 20 to 80%.

Short summary
We use a new risk analysis method, and six vegetation models, to analyse how climate change may alter drought risks in European ecosystems. The conclusions are (1) drought will pose increasing risks to productivity in the Mediterranean area; (2) this is because severe droughts will become more frequent, not because ecosystems will become more vulnerable; (3) future C sequestration will be at risk because carbon gain in primary productivity will be more affected than carbon loss in respiration.
Final-revised paper