The Mediterranean region is one of the areas in the world that is recognized as a hot spot not only for climate change but also more generally for global change. Indeed, the Mediterranean land surfaces and their associated socio-ecosystems are facing large modifications linked to an increase in drought frequency (Hoerling et al., 2011); to an ever-increasing population, from 370 million in 2000 to probably 560 million in 2030 (Ludwig et al., 2010); and to intense migration to coastal cities (Mediterra, 2008). The future of the Mediterranean socio-ecosystems is therefore questionable. It is even more so because for many years now, their natural resources have been under pressure and became insufficient in many countries when compared to the needs of the populations. The situation is expected to worsen and favor large social tensions, within and between the Mediterranean countries. Water resources are drastically lacking in the southern and eastern Mediterranean countries where 108 million inhabitants are considered water-poor (< 1000 m3 cap−1 year−1), and 58% of these live with water shortage (< 500 m3 cap−1 year−1) (Blinda and Thivet 2009). Anthropogenic water withdrawals now amount to a large proportion of the annual renewable water resources (Milano et al., 2013). The Mediterranean region also experiences a deficit in agricultural production: for example, in 2003, the Mediterranean basin imported up to 22% of the world imports of cereals but represented only 7% of the world population (Mediterra, 2008). Moreover, arable land is scarce which leads in several countries to the expansion of intensive agriculture, whether irrigated or rainfed, towards marginal land that can degrade when too intensively exploited (Mediterra, 2008). This is amplified by the fast urbanization of coastal areas where soil artificialization decreases arable land. Consequently, the present trends towards an intense exploitation of the natural resources of the Mediterranean ecosystems are likely to put strong pressures on their hydrological and biogeochemical cycles (e.g., carbon, salts, trace elements, xenobiotics) and exacerbate their degradation. Seeking sustainable development in the Mediterranean region requires improving deeply our understanding of the processes of degradation, resilience, and restoration of the variety of Mediterranean socio-ecosystems.

In 2010, the international research initiative Mistrals (http://www.mistrals-home.org/) was launched for studying over a decade the environmental behavior of the whole Mediterranean basin submitted to global change. In the framework of Mistrals, several sub-initiatives took place. One of them, SICMED (Surfaces and Interfaces of the Continental MEDiterranean, www.sicmed.net) was supported by the following French research institutes: CNRS-INSU, INRA, IRD, and IRSTEA. It aimed at developing a regional cooperation process for long-term research on the present and future states of rural and peri-urban Mediterranean socio-ecosystems under climatic and man-induced changes. This included the joint study of biophysical processes governing the hydrological and biochemical cycles, and of social, economic, and institutional processes driving the human activities impacting the cycles. It also included the implementation and progressive development of a network of socio-ecosystem observatories where observations of biophysical and social dynamics can be linked. It was expected that the simultaneous consideration of the biophysical and socio-economic drivers of the Mediterranean ecosystems will both improve our understanding of the existing changes and enable to identify the levers and develop tools and methodologies for a better management of natural resources and territories. Nine research projects were operated from 2011 to 2015 during the first phase of the SICMED initiative. Over that period, the projects gathered 59 research teams from nine countries (Algeria, Canada, Spain, France, Italy, Lebanon, Morocco, Portugal, Syria, Tunisia). More than 130 papers describing primary research results in the fields of hydrology, soil science, ecology, and social sciences were published by the research teams in a variety of international scientific journals and books. For this supplement of Regional Environmental Change, we asked the researchers of the SICMED network to join their expertise, acquired in a variety of Mediterranean contexts, for proposing multidisciplinary perspectives on the current state of Mediterranean socio-ecosystems, on the upcoming challenges these have to face and the solutions that can be put forward. The supplement finally brings together six papers focusing either on specific socio-ecosystems or on the management of soil and water resources.

Gauquelin et al. (2016) review the specificities of Mediterranean forests in terms of soil, climate, biodiversity, and ecological functioning. They mention that most forests are the result of a long history of agro-sylvo-pastoral management and forest state administration, which leads to contrasted ecosystem dynamics in different countries or regions on the northern and southern shores of the Mediterranean basin. The comparative analysis of the dynamics of four different tree species shows that local societies used to manage forests in a sustainable way that are now threatened by the current socio-economical transformations. Forests are at risk but also represent a great capital for the Mediterranean region. So, to preserve this capital but also to exploit the opportunities it provides, the paper advocates a need of a comprehensive and multidisciplinary approach that links academic and applied sciences and considers ecological or cultural aspects.

Souissi et al. (2017) question the performance of Mediterranean farming systems to face climate change. They use an integrated modeling chain combining biophysical, bioeconomic models and selected indicators for performance analysis. Its application on representative Tunisian farming systems shows interestingly that the most diversified farming systems (cereals, forage, and livestock) are the most resilient to climate change. It illustrates the importance of preserving biodiversity in the farming activities, which offer adaptation possibilities to changes in water resources and market opportunities.

Given the constant and fast growth of urban zones on the coastal Mediterranean regions, often at the expense of arable land, the evolution of the urban agrosystems and their link with local food security become important issues. Soulard et al. (2017) compare six case studies of peri-urban agro-ecosystems in southern Europe and Maghreb. Like other types of socio-ecosystems in the Mediterranean, the peri-urban systems exhibit a large diversity of forms and dynamics driven by global and local factors. The paper shows that the urban pressure favors an increase in the agricultural diversity, enabling better adaptation capacities of the peri-urban agrosystems. However, the resistance or decline of urban agriculture also appears to depend on whether the urban policies and actors recognize its interest for local food security, agricultural jobs, and environmental protection.

The sustainable management of soil resources is evidently a major issue for the preservation of the Mediterranean ecosystems. Lagacherie et al. (2017) review several types of degradation (e.g., erosion, salinization, loss of carbon content) that Mediterranean soils can be subjected to in relation with global change. A number of mitigation strategies exist but the authors emphasize the need of site-specific choice and adaptation of these strategies. To this aim, they point out a major lack of soil information at a fine resolution. Given the short-scale variability of Mediterranean soil, this is a crucial issue. More generally, it has to be noticed that environmental data remain sparse and/or without open access in Mediterranean countries. This is a serious limitation for both increasing knowledge about ecosystem functioning and seeking innovative management strategies adapted to local conditions.

Doumas et al. (2016) focus their literature review on the environmental and health problems which can arise from the exploitation of mineral resources in the Mediterranean area. Industrial development is here often lower compared to other regions of the world, but mining activities in combination with the environmental and socio-political peculiarities in this region can be a significant threat for human health. Especially, abandoned mines are a recurrent problem for nearby populations because they can be a major source for polymetallic pollution. Dispersal of these contaminants via dust and acid drainage waters is not only controlled by the prevailing geological, geochemical, and climatic conditions, but also by the degree of public concern on environmental problems and the resulting legal regulations constraining these sites. Nevertheless, the paper also demonstrates that novel technologies such as phytostabilization of mine tailings are possible and should be further explored by future research efforts.

Aït-Mouheb et al. (2018) compare the water reuse practices for irrigation in four Mediterranean countries (France, Italy, Jordan, Tunisia) and discuss the combined scientific and social issues that need to be addressed for a sustainable reuse of treated wastewater. Reuse of reclaimed water is clearly an opportunity to limit water shortage and contribute to a more circular economy framework. Its expansion and regulation vary largely between countries following their level of water stress. But whatever these differences, the paper underlines a general challenge for the treatment industry that is to go beyond the sole minimization of the impacts of reclaimed water on the environment and health and to add value to reclaimed water by better fitting its characteristics to the agricultural needs, in nutrients for example.

Each of the papers presented above underlines the large diversity in terms of natural resources, historical trends, and cultural heritages and the resulting variety of states and fates of Mediterranean ecosystems. All together, they provide a clear scientific demonstration why there is an urgent need to focus our research efforts on the Mediterranean region in the domain of global change. It becomes evident that this area is characterized by two antagonistic trends which strongly increase competition and pressure on natural resources and environmental vulnerability compared to other regions of the world. In terms of climatic characteristics, the North actually shifts towards the South and the East. Global warming leads to higher average temperatures, increased aridity, and increased water scarcity, and conditions may therefore resemble those currently found in southern basins. In terms of socio-economic development and lifestyle, the South and the East move towards the North. Not only the intensification of agriculture and the expansion of irrigated land will be comparable to the conditions found in northern regions, but also dietary habits and lifestyles are changing to approach those in the North. Consequently, it is essential to explore the diversity of trends and situations between the different parts of the Mediterranean for comparing the drivers of ecosystem adaptation to global change in different contexts and learning from each other.

The urgent need for additional collaborative research efforts is also true because knowledge gaps are particularly striking here. Hot spots for the expected ecosystem and societal shifts mainly arise in the South and the East, where research efforts in the past were often inexistent because of the lacking of economic resources in these countries compared to the North. Programming our further research activities is therefore not only the challenge of an intelligent design according to fundamental research questions, but also the challenge of the successful transfer of knowledge and technology and of equitable cooperation between all academic and non academic actors in the Mediterranean drainage basin. Strengthening of networks between scientists from different Mediterranean countries in order to overcome the inherent limitations of single-case studies was consequently one of the major motivations of the SICMED initiative. Finally, confrontation of the six papers in this volume also demonstrates the close interconnections which exist in the Mediterranean area between the domains of water resources, ecosystem shifts, food production, and human health. This can strongly amplify negative feedbacks of change and requires novel and multidisciplinary efforts between natural and social scientists in the domain of environmental research.