Riparian vegetation responses to altered flow regimes driven by climate change in Mediterranean rivers Rui Rivaes, 1 * Patricia M. Rodríguez-González, 1 António Albuquerque, 1 António N. Pinheiro, 2 Gregory Egger 3 and Maria Teresa Ferreira 1 1 Centro de Estudos Florestais, Instituto Superior de Agronomia, Technical University of Lisbon, Tapada da Ajuda, 1349-017 Lisboa, Portugal 2 CEHIDRO, Instituto Superior Técnico, Technical University of Lisbon, Av. Rovisco Pais, 1049-001 Lisboa, Portugal 3 EB&P Umweltbüro GmbH, Bahnhofstrasse 39, 9020 Klagenfurt, Austria ABSTRACT Mediterranean regions are characterized by a large intra-annual and inter-annual variability in rainfall and associated hydrological regime patterns. Predictions of changes in climate indicate that mean precipitation and annual temperature will both increase, with a concentration of precipitation and the existence of extended and harsher drought periods with profound implications for river ecosystems. Our aim in this study was to predict the response of Mediterranean riparian vegetation to different climate change scenarios, using a dynamic riparian vegetation model that relates flow regime with riparian vegetation dynamics. In our case study, mapped riparian patches were significantly distinct in between, and altitude, height above water table, patch age and stem diameter were the most important of the factors that distinguished succession phases. A floodplain vegetation model was calibrated and achieved a good strength of agreement between simulated and observed maps. Model results with the expected flow regime under the effect of climate change demonstrate that nonwoody sparsely vegetated areas expand outwards and mature succession patches expand inwards, whereas pioneer and young riparian patches decrease in area. Our results suggest that extreme climatic change in Mediterranean rivers will promote the disappearance of the pioneer and young succession stages of riparian woodlands, thus making efforts to conserve these ecosystems a challenging task. Copyright © 2012 John Wiley & Sons, Ltd. KEY WORDS floodplain vegetation; fluvial disturbance; hydrologic regime; predictive model; vegetation succession; climate change; CASiMiR-vegetation Received 11 October 2011; Revised 18 May 2012; Accepted 21 May 2012 INTRODUCTION Since the beginning of the 20th century, the average global atmospheric temperature has been rising, and the speed with which it has been doing so has also increased (McCarthy et al., 2001). Global temperatures are expected to rise significantly in this century, even if greenhouse gas concentrations remain constant at year 2000 levels. Over the next hundred years, this will induce changes in the global climate system that will very probably be of a greater magnitude than those observed during the last hundred (Solomon et al., 2007). For Mediterranean regions, most Global and Regional Circulation Models that simulate the Earth’s climate system predict an increase in mean annual temperature and a decrease in mean annual rainfall, with a concentration of precipitation in a short period of a few months each year and with extended and harsher droughts (IPCC, 2001). The alteration of hydrological regimes may be as deleterious to ecosystems as temperature changes (Schröter et al., 2005), particularly in the case of river systems (Palmer et al., 2009). The principal attributes of the Mediterranean- type climate are seasonality and variability of rainfall, with seasonal flooding as a typical feature (Gasith and Resh, 1999). Inter-annual variability is represented by changes in the frequency of floods and variations in annual rainfall, whereas intra-annual variability (seasonality) is represented by periods of water surplus interspersed with hydric scarcity. Even the most tenuous climatic changes can result in major alterations in the river flow regime, such as changes in the frequency of the recurrence of extreme floods (Sánchez et al., 2004). It is also expected that changes in natural flow regimes due to climate changes will be magnified by human efforts to satisfy water demand on the part of populations, such as water retention in reservoirs (McCarthy et al., 2001; Malmqvist and Rundle, 2002; Arthinghton et al., 2006). European Member States are nonetheless being asked to actively improve the resilience of ecosystems in the face of climate changes (CEC, 2009; Biesbroek et al., 2010), with proactive conservation efforts centred on maintaining ecosystem functioning, climate mitigation and adaptation (Palmer et al., 2008; Woodward et al., 2010). Riparian vegetation is a characteristic component of river systems and ensures a liaison between the river channel and the terrestrial ecosystems (Naiman and Décamps, 1997). The structure of this ecotonal zone and its lateral and vertical hydric connections are strongly *Correspondence to: Rui Rivaes, Centro de Estudos Florestais, Instituto Superior de Agronomia, Technical University of Lisbon, Tapada da Ajuda, 1349-017 Lisboa, Portugal. E-mail: ruirivaes@isa.utl.pt ECOHYDROLOGY Ecohydrol. (2012) Published online in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/eco.1287 Copyright © 2012 John Wiley & Sons, Ltd.