Visualising multiple stressors on European river catchments: the MARS Scenario Analysis Tool

The MARS Scenario Analysis Tool

Over the last four years, the MARS project has been investigating the interactions and impacts of multiple stressors on Europe’s aquatic ecosystems. This is a topic at the cutting edge of freshwater science research, and MARS scientists have sought to understand how the multiple pressures humans place on the environment – nutrient pollution, habitat alteration, climate change, water abstraction, and many more – act together to cause stress on the continent’s rivers and lakes. As a result, this work is important for environmental managers and policy makers seeking effective options to mitigate multiple stresses, and conserve or restore Europe’s freshwaters.

MARS Scenario Analysis Tool

MARS has recently launched its Scenario Analysis Tool – an online, open-source mapping tool, which allows users to visualise and analyse multiple stressor conditions in European rivers. The tool can generate maps showing where different stressors occur, how many stressors co-occur, and their potential impacts on ecosystem status, at both the river basin and the continental scale.

The Scenario Analysis Tool shows that six stressor indicators – 1) dissolved inorganic nitrogen and 2) phosphorous concentrations; surrounding 3) urban, and 4) agricultural land; alterations to 5) annual and 6) base water flows – explain the majority of differences in ecological status across European rivers. MARS researchers also identified ecological thresholds when the impact of multiple stressors tips ecological status from good to moderate.

Current Stressor Patterns in European Rivers

The Scenario Analysis Tool illustrates a number of broad current European stressor patterns. It shows that Southern Europe is significantly more hydrologically stressed than the rest of Europe, particularly in Mediterranean countries as a result of water abstraction for agriculture. There are three or more stressors acting together in half of the European river catchments. Only 9% of European river catchments have no active human stressors acting on them.

Stressor ‘thresholds’ where ecological status is reduced were found in 60% of catchments for agricultural land use stressors, 50% of catchments for dissolved inorganic nitrogen, and 40% of catchments for total phosphorous. This is unsurprising, as nutrient modelling underpinning the tool shows that agriculture is a significant source of nutrient loadings into European rivers.

Visualisations of the multiple stressors impacting individual river basins can be created by users. This complex picture is for the Danube basin.

Storylines for Future Worlds

The Scenario Analysis Tool also allows users to visualise the multiple stressor picture for two future periods – 2026–2035 and 2056–2065 – under two different ‘storylines’ of possible climatic and social change. The two time-horizons have been chosen to inform the update of the Water Framework Directive in 2027 (2026–2035), and to show possible impacts of climate change (2056–2065). The two storylines have been designed by MARS researchers to outline possible future climatic, political and economic trajectories, based on forecasts in the IPCC Representative Concentration Pathways and Shared Socio-Economic Pathways.

The Techno World storyline is based on a scenario of high greenhouse gas emissions and rising global temperatures (Representative Concentration Pathway 8.5) in combination with a strong, carbon-based global economy in which many currently pressing social concerns, such as inequality and population growth, have been mitigated (Shared Socio-Economic Pathway 5).

The Consensus World storyline is based on a scenario where future development follows similar patterns to the recent past: the economy grows well in some countries and poorly in others, and inequality between rich and poor countries continues. Despite this disparity, the world tends towards being relatively politically stable (Shared Socio-Economic Pathway 2). This occurs alongside a stabilising and relatively low level of climatic change (Representative Concentration Pathway 4.5).

In addition to the future ‘storylines’, the Scenario Analysis Tool allows for the effects of three stressor mitigation management approaches – nutrient reductions, riparian buffer strips, and improved waste water treatment – to be modelled.

Forecasting dissolved inorganic nitrogen concentrations in the River Thames basin in SE England under the Consensus World scenario around 2060.

Future ‘Storyline’ Stressor Patterns

Both Techno and Consensus World storylines predict that river discharges are likely to increase, on average, across European catchments in the future. The highest increases will occur during high flow season, and the lowest increases during low flow season. However, in several rivers in Southern Europe, discharge in the low flow season will decrease in both storylines.

For both storylines, the probability of rivers reaching good ecological status falls by 3–5% in the future if mitigation strategies aren’t implemented to manage stressor effects. However, this prediction differs with river type. This finding emphasises the need for catchment specific stressor mitigation approaches, rather than a ‘one size fits all’ European water management approach.

Data and Models

The Scenario Analysis Tool is underpinned by two computer models using hydrological, ecological and meteorological data gathered between 2001-2010. The global hydrological model PCR-GLOBWB was used to simulate river flows and runoff across Europe. Water abstraction, reservoir management and domestic, industrial, livestock and irrigation water use are all included in this model. This feeds hydrological data to a second model, MONERIS, which quantifies nitrogen and phosphorus emissions to surface waters, along with their in-stream retention rates, and resulting loads and concentrations.

The results of both models are brought together with data on individual catchments, and the Water Framework Directive reporting data on ecological status by EU member states. The outputs of this computer modelling allows for climate, water availability, nutrient fluxes and management options to be analysed through quantifying and evaluating multi-stressor conditions and aquatic responses across Europe.

The tool was designed and developed by Markus Venohr and Judith Mahnkopf from IGB (DE), supported by Lidija Globevnik (Uni Ljubljana, SI), Yiannis Panagopoulos (NTUA, GR), and Marta Faneca Sanchez and Frederiek Sperna Weiland (Deltares, NL).

Explore the Scenario Analysis Tool

Read the MARS report on the methods, data and results of the Scenario Analysis Tool