ORIGINAL ARTICLE Climate change impacts on vegetation and water cycle in the Euro-Mediterranean region, studied by a likelihood approach M. Santini • A. Collalti • R. Valentini Received: 22 January 2013 / Accepted: 29 December 2013 Ó Springer-Verlag Berlin Heidelberg 2014 Abstract Scientific community and policy-makers share the common interest in identifying and evaluating potential impacts of climate change on ecosystems, relying mainly on probabilistic methods of exploring the risks. In this perspective, the concept of ensemble forecasting makes possible to handle uncertainties associated with climate risk analysis by focusing on a range of potential or prob- able impact scenarios rather than actualizing a single case. In this paper, an ensemble of simulations based on the Lund-Potsdam-Jena (LPJ) model was used to investigate the uncertainty upon predictions of the future Euro-Medi- terranean vegetation distribution, carbon dynamics, and water budget. Twenty simulations from past to future were based on the combination of different climate inputs, vegetation model parameterizations, and configurations. The evaluation of results combined the separate deter- ministic future projections from the LPJ model into a single probabilistic projection, associating a likelihood degree in accordance with the most recent Intergovernmental Panel on Climate Change terminology. Results projected a general critical situation in terms of water availability, made more serious if considering that also the occurrence of extreme-related events, e.g., fires, is expected to become more frequent as favored by more recurrent drought epi- sodes. Although more uncomfortable climate conditions were projected for vegetation, net primary production (NPP) was predicted to increase due to the potential enrichment of CO 2 in atmosphere and its fertilization effects on vegetation. The combination of rising NPP and fire frequency may shape the carbon cycle components, as the carbon losses by fire also were projected to increase. Keywords Ensemble projections Á Likelihood Á DGVM Á Euro-Mediterranean area Á IPCC Introduction Climate risk assessment is a complex and relevant issue as it covers multiple dimensions and aspects, involving dif- ferent regions, sectors, and resources. Scientific community and policy-makers share the common interest in identifying and evaluating potential impacts of climate change on ecosystems, relying mainly on probabilistic methods of exploring the risks. Climate risk assessment is a strictly future-oriented practice with a considerable degree of uncertainty, challenging the process of decision making on mitigation and design of adaptation strategies (Ra ¨isa ¨nen and Palmer 2001). The synthesis chapter of the Third Assessment Report by Intergovernmental Panel on Climate Change (IPCC) emphasized limitations of traditional climate change impact assessments based on the evaluation of potential single scenarios and system responses (Smith et al. 2001b). If the model simulations’ uncertainty is not properly Electronic supplementary material The online version of this article (doi:10.1007/s10113-013-0582-8) contains supplementary material, which is available to authorized users. M. Santini (&) Á A. Collalti Á R. Valentini Division on Impacts on Agriculture, Forest and Natural Ecosystems (IAFENT), Centro Euro-Mediterraneo sui Cambiamenti Climatici (CMCC), via Antonio Pacinotti 5, 01100 Viterbo, Italy e-mail: monia.santini@cmcc.it M. Santini Á A. Collalti Á R. Valentini Department for Innovation in Biological, Agro-Food and Forest Systems (DIBAF), University of Tuscia, via San Camillo de Lellis snc, 01100 Viterbo, Italy 123 Reg Environ Change DOI 10.1007/s10113-013-0582-8