Polski
Issue 4/2026, From the European Commission, Issue 4/2026, From the European Commission
Ecological status in a changing climate – JRC report
Apr
In March this year. The European Commission’s Joint Research Center (JRC) has published the report Ecological status in a changingclimate. It summarizes the work of experts gathered around the Ecostat working group at the Directorate General for Economic and Financial Affairs. The European Commission’s Environment Directorate-General. On September 30, 2025, a workshop was held in Copenhagen to accompany the Ecostat working meeting, which was attended by, among others, the writer of these words, and summarized in the JRC report.
Impact of climate change on water levels
The basis for assessing ecological status is the provisions of the Water Framework Directive (WFD). It was adopted in 2000, when knowledge of climate change was already established among climatologists, but still poorly established among decision-makers, including those creating the WFD. For this reason, the directive’s provisions stipulate the immutability of reference conditions for ecological status. Meanwhile, the condition that was natural at the end of the 20th century may no longer be achievable in the foreseeable future.
Climate change has become a pressure multiplier that is redefining the way we assess the health of aquatic ecosystems. This creates a temptation to blame any failure in the path to improving water status on climate change. The magnitude of its impact must therefore be properly assessed and incorporated into the water assessment system. The main challenge is to distinguish whether the biological deterioration of waters is due to local human activities (which we can control) or to irreversible climate shifts.
According to the JRC report, the impact of climate on water is multifaceted. Higher air temperature directly affects water thermics, which in turn modifies physicochemical and biological processes. Accelerated snowmelt and more frequent episodes of torrential rainfall cause rapid surface runoff of pollutants from the catchment, while higher evaporation reduces the amount of water in the riverbed. Warm water and slowed flow promote algal blooms. This means that nutrient concentrations that used to guarantee good condition may now be insufficient to prevent biological degradation. As temperatures rise, oxygen solubility decreases, leading to anoxia, which is particularly dangerous for ichthyofauna and macroinvertebrates.
Possible scenarios for incorporating climate change into water assessments
Ecostat/JRC experts have prepared four strategic scenarios to help member states adjust their monitoring systems:
- Status quo with adaptation of norms (evolutionary);
- Reform of typology and reference conditions;
- separation of pressures;
- Climate change as a new quality element.
The easiest way, because it doesn’t require new analysis, would be to leave things as they were. However, this does not agree with the requirements of the WFD, which mandates the renewed creation of water characteristics. One cannot pretend that the baseline has remained the same. For example, if under the new conditions eutrophy occurs at lower concentrations of nutrients than before, the standards for them should be tightened.
Another approach to climate change involves reforming surface water typologies. In the case of watercourses, this could be changes in flow constancy, in the case of lakes in their size and mictic type. The disadvantage of this is the difficulty of comparing results from different periods, but there is unlikely to be any other way. On the other hand, while this allows realistic targets to be set, it runs the risk of lowering ambitions, because considering a river as periodic can become an excuse for abandoning corrective measures to restore its steady flow.
The third way out is the analytical approach, which uses modeling to indicate how much of the bad condition is due to climate change and how much is due to other pressures. This approach, while theoretically attractive to policymakers, is extremely difficult to implement because of the non-linear interactions between temperature change and other pressures.
A rather exotic scenario, and one that goes beyond the current legal framework of the WFD, is to consider climate change as the third (besides physicochemical and hydromorphological) group of elements supporting the status of biological elements. It would require rebuilding the classification system and breaking the historical continuity of the data. The main concern is that it would introduce into the compilation an element whose status cannot be improved by water management measures.
JRC report: case studies
The report cites case studies raised at the workshop. One concerned the Czech Republic, although similar phenomena are observed in other countries, including Poland. Many streams have changed their character from permanent to periodic. The lack of appropriate reference conditions for such streams makes their classification (based on macroinvertebrates in the example discussed) come off as poor, even though this may be the natural response of the biocenosis to the lack of water. Some Mediterranean countries have already managed to modify their methodologies, adapting them to the intermittent nature of watercourses.
Climate change means not only droughts, but also floods. The associated seasonal variability of flows makes timely monitoring of phytoplankton impossible, requiring not so much changes in typology as in sampling methodology and schedules themselves. The Oder catastrophe was also presented as an example of ecological status problems resulting from climate change. Its analysis showed that climate change (high temperature, low flow) drastically reduced the ecosystem’s resistance to salinity, leading to a massive bloom of Prymnesium parvum. Importantly, despite the return of fish biomass, the species composition has changed. The consensus was that in the case of the water bodies that make up the Oder River, there is no basis for a typological change and the problem lies with water management rather than climate change.
A key point of contention among experts is the definition of irreversibility. While sea level rise and the resulting salinity of transitional waters are considered permanent, changes in river flows have been defined as more fluid. This raises the question of whether hastily declaring a watercourse to be intermittent takes away its chance to return to its original state through better retention management.
Different voices resounded in the national delegations – from a proposal to abandon monitoring of watercourses that have dried up permanently, to a position mandating that dry riverbeds be treated as integral elements of the hydrographic system and in need of protection. The JRC report and workshop discussions suggest that the WFD system needs to become more flexible. The immediate future will belong to an evolutionary scenario, supported by the update of the 24th Interpretive Guide to this directive River basin management in a changing climate.
The main conclusions are as follows: Member countries should take advantage of the opportunity to update water types every 6 years, based on sound scientific evidence and not just administrative convenience. It is recommended that individual quality elements be analyzed and reported separately, rather than based solely on a worst-case decider basis, to better understand climate impacts. Given the inertia of planning systems, the methodological changes planned today will only find full application in a dozen years or so.
In preparing the article, I used:
24 WFD Joint Implementation Strategy Guide: River basin management in a changing Climate, 2024, https://circabc.europa.eu/ui/group/9ab5926d-bed4-4322-9aa7-9964bbe8312d/library/b5f4eff8-2482-4494-9df0-e72cb8792e19/details
JRC Report: “Ecological Status in a Changing Climate,” 2026, https://publications.jrc.ec.europa.eu/repository/handle/JRC146177
