As a first assessment, based on various sources of information, Cramer et al. (2018) have shown that the Mediterranean Basin is at risk of suffering from levels and rates of climate and environmental changes now and in the foreseeable future that exceed global mean values. This applies to changes in temperatures, precipitation and the frequency and magnitude of extreme weather events, but it also implies changes in land and sea use, pollution, air quality and other factors. Average annual mean temperatures in the Mediterranean Basin have risen by 1.5°C since pre-industrial times (1861-1890), approx. 0.4°C above the global average (Chapter 2), due to a combination of local drivers (e.g., land use changes) and changes on a global scale that affect the Mediterranean Basin through various modes of tele-connectivity (Lionello et al. 2014).

Desertification is in fact the result of two different factors in origin operating in combination, prolonged drought of climatic origin and land exploitation of human origin (Le Houérou 1996). In Mediterranean arid lands, mainly during the 20th century, short-term planning of agricultural policies and overexploitation, mainly in the form of overgrazing but also fuelwood collection and ground water exploitation, contributed to soil quality decline and massive erosion. Deteriorating conditions have a great impact on the lives of inhabitants of Mediterranean drylands and force most of them to migrate (Mohamed and Squires 2018) (Sections 3.2.1.4, 4.3.1 and 6.6).

Although droughts have been a common experience for most of the history of the Mediterranean, the recently observed decline of seasonal precipitation for parts of the Basin (Chapter 2) presents new and significant challenges for Mediterranean communities. While most climate models show remarkable agreement in the expected decrease in Mediterranean rainfall, there are also some results indicating significant differences in magnitude and sign for these changes. Even if future global warming is limited to 2°C, as prescribed by the UNFCCC Paris Agreement, summer rainfall risks being reduced by 10-30% in some regions. Such a decrease will enhance existing water shortages and increase irrigation demand for agricultural productivity, particularly in countries on the southern rim of the Basin .

Climate change, population growth, increasing domestic needs and pressure from tourism, new industries and urban sprawl may see irrigation demand rise by 26-92% by the end of the 21st century (Fader et al. 2016). Although frequently addressed by policy-makers, irrigation and food security remain a sensitive issue that needs additional research (Grafton et al. 2018; WWAP 2019). Research into the extent to which local landraces can cope with projected climate changes without significant loss of productivity should be a priority (FAO 2015). More aridity exacerbates ongoing desertification, with strong socio-economic impacts on farmers (UNEP/MAP 2016).

Emissions of aerosols and particulate matter (PM) into the atmosphere arise from a variety of anthropogenic activities. Particular meteorological conditions and natural sources, including the proximity of the Sahara Desert, create particular patterns of aerosol concentrations that may influence particulate matter PM concentrations. The occurrence of critically high PM concentrations associated with dust outbreaks is higher in the southern Mediterranean (>30% of the annual days) than in the northern area (<20% of the annual days)

The interlinkages between resources have been addressed through the concept of the Water-Energy-Food Nexus (e.g., Hoff 2011; Kennou et al. 2019), but they still present unresolved challenges. Since the impacts of climate change are likely to include the degradation of agricultural water resources and loss of fertile soils, enhanced efforts to adapt agricultural and other land systems to climate change are necessary to ensure food security and rural livelihoods (UNEP/MAP 2016). Despite this reduction, extreme precipitation events are expected to intensify in a large part of the region. Therefore, flood socio-economic and environmental impacts should be added to those produced by water scarcity.

The First Mediterranean Assessment Report (MAR1) prepared by the independent network of Mediterranean Experts on Climate and environmental Change (MedECC) founded in 2015 is now finished. MedECC assesses the best available scientific knowledge on climate and environmental change and associated risks in the Mediterranean Basin in order to render it accessible to policymakers, stakeholders and citizens. The report includes a Summary for Policy-makers (SPM), which comprises the key messages of the MAR1.

The report has been written by almost 190 scientists from 25 countries, all contributing in individual capacity and without financial compensation. The MedECC coordinators are very grateful for the expertise, rigor and dedication shown by the volunteer Coordinating Lead Authors and Lead Authors, working across scientific disciplines in each chapter of the report, with essential help by the many Contributing Authors. MedECC Authors and Coordinators want to thank all reviewers for their time and effort.

The UNEP/MAP – Barcelona Convention Secretariat, through its Plan Bleu Regional Activity Center, and the Secretariat of the Union for the Mediterranean work in partnership to support MedECC, and to contribute to establish a sound and transparent scientific assessment process. Many other institutions (specified in the “Front matter” and the Annex A of the report) also supported the preparation of this report.