There is a critical link between reduced river flow into the Mediterranean and the health of the Mediterranean marine ecosystems. New research underscores the urgency of integrating water resource management to properly safeguard the rich biodiversity of seas and ocean and the economies it supports.
Climate change impacts such as more frequent and more severe prolonged droughts due to lack of precipitation and high evaporation are expected to exacerbate water stress (the inability to meet water demand) in Europe: around 20 % of Europe’s territory and 30 % of its population experience water stress every year.
A new study led by JRC scientists investigates the impact of decreased river water flow on marine ecosystems in the Mediterranean due to climate change and growing demands for water.
In Europe, the impact of climate change would worsen freshwater flow in rivers and water stress, particularly in the south and southwest. The river Po in Italy, which flows into the Mediterranean, has already experienced critically lower level of water flow multiple times.
Its water volume was nearly halved on at least five occasions over 23 years of monitoring (2001 - 2023). In 2022, the drop in water flow reached a record low of 39% of its mean value during the monitoring period.
To limit temperature rise and tackle a changing climate, the EU has put in place targets and strategies to lower its emissions by at least 55 % (compared to 1990 levels) by 2030 and become climate-neutral by 2050. As one of its key political priorities in 2025, the European Commission is preparing a Water Resilience Strategy to boost efforts and ensure the security of water supply, reduce flood risks, and mitigate drought impacts.
The study, published today in Nature Communications, examines the impact of an extreme scenario of unchecked climate change and global temperature rise of 4 °C above pre-industrial levels (defined by the United Nations as the RCP 8.5 warming scenario), which could result in 41 % less river flow into the Mediterranean.
Low river flows in the seas like the Mediterranean mean a profound alteration of the coastal ecosystems due to reduced freshwater and nutrients inputs that lead to a decrease in primary productivity of the system. This decrease of productivity in the base of the trophic chain propagates upwards affecting the whole food chain and reaching the commercially exploited seafood species.
The results show that 41% less river flow could slash marine productivity by 10 % and fish biomass by 6 %, in the Mediterranean and lead to annual losses worth €4.7 billion to the fishery sector. This would bring about dire socio-economic consequences for fisheries and coastal communities.
The regional Adriatic and the Aegean Seas, which appear to be particularly vulnerable to global warming, could see reductions in marine productivity and fish biomass of 12 % and 35 %, respectively. These areas are among the most intensely fished regions in the Mediterranean Sea.
The study used the JRC-designed Blue2 Modelling Framework (Blue2MF) to assess the impacts of reduced freshwater flow on the Mediterranean Sea's biogeochemistry, food web and socio-economic sectors. The findings indicate that the most productive and heavily fished regions, such as the Adriatic and Aegean Seas, are at the highest risk, with potential biomass losses exceeding their current fishery landings.
Background
The Mediterranean Sea, a biodiversity hotspot and a cornerstone of the region's economy, faces unprecedented challenges due to climate change and increasing demand for water.
EU legislation, including the Urban Waste Water Treatment Directive, the Water Framework Directive and the Marine Strategy Framework Directive, recognises the importance of environmental flows for maintaining coastal ecosystems, but discussions on water management typically do not consider these needs. Freshwater reaching the oceans is generally considered to be ‘lost’ by many stakeholders.
This new study provides a crucial understanding of the potential impacts of water scarcity, informing policymakers and stakeholders about the need for sustainable water management practices that consider the entire water cycle, from source to sea.
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