(c) Assessing cumulative effects with other plans and projects
Cumulative impacts can result from the successive, incremental, and/or combined effects of a development (plan, project) when added to other existing, planned, and/or reasonably anticipated developments (see also section 3.1.4, table 2 on the key steps for assessing cumulative effects on a Natura 2000 site). Examples of cumulative impacts include: increased pollutant concentrations (particularly in water and soil), beyond levels compatible with the ecological requirements of the habitat or species protected in the site; reduction of water flow in a watershed due to multiple withdrawals, below the level which is compatible with the ecological requirements of the habitat or species protected in the site; interference with migratory routes or wildlife movement; increased pressure on habitats and species in an ecosystem from different developments. Cumulative impacts encompass a broad spectrum of impacts on different geographical scales and timeframes. In some cases, cumulative impacts occur because a series of projects of the same type are being developed. Prime examples are: when several hydroelectric projects are constructed or planned on the same river or within the same watershed; when multiple oil and gas projects or mineral extraction projects are developed in close proximity; or when a number of wind farms are constructed or planned within the same flyway or region. In other cases, cumulative impacts occur due to the combined effects of different types of projects in the same area, such as the development of a mineral extraction site, access roads, transmission lines, and other adjacent land uses. In some situations, different components of the same development are implemented and assessed separately, meaning that the cumulative impacts from these components should also be subject to a cumulative impact assessment. Other plans or projects that could, in combination with the plan or project under investigation, have a significant effect on a site must be taken into account during the appropriate assessment. For example, a proposed road will pass some distance from a Natura 2000 site and the disturbance it will generate (e.g. noise) will not significantly affect bird species protected in the site. However, if there are other existing or proposed projects or plans (e.g. a road on the other side of the Natura 2000 site), then the total noise levels from all these projects combined may cause a significant level of disturbance for those bird species (noise levels above what it compatible with the ecological requirements of the species). To note also that cumulative impacts could occur where impacted areas interact. An example of this would be where a proposed project is likely to reduce water levels in a Natura 2000 site. Although that resource reduction in itself may not be significant, if existing fertiliser and pesticide residues reach the site from a nearby intensive farming area, the lower water levels may mean higher concentrations of pollutants when run-off occurs, to an extent that the combined effect becomes significant, i.e. concentrations of pollutants beyond the levels which are compatible with the ecological requirements of the habitat or species protected in the site. ‘In-combination’ effects should already have been investigated at the screening stage (Section 3.2), and any other plans and projects that can act in combination should have been identified. The assessment at the screening stage may have been simplified, but, at the appropriate assessment stage, the identified impacts of other projects or plans that can act in combination with the plan or project being assessed should be properly evaluated. This requires quantifying and/or qualifying the magnitude of these other impacts and identifying the affected features of the Natura 2000 sites. As stated in section 3.1.4, the in-combination provision concerns other plans or projects that have been already completed, approved but not yet completed, or submitted for consent. The geographical scope to use when looking at cumulative effects will depend on the type of plan or project and the habitats and species significantly present on the site. It could be, for instance, within a certain radius, on a catchment area basis, or along a bird migration route. It should however cover the entire geographic area in which all plan or project activities and their cumulative effects are likely to have implications on the conservation objectives of the Natura 2000 sites in question. Plan level assessments are particularly suitable for assessing cumulative and synergistic effects since they can pre-empt problems further down the line at the project stage, e.g. in the case of plans for specific sectors such as transport, energy, water management, as well as regional plans and strategies, land use plans, etc. In this context, it can be particularly useful to consult the environmental assessments of other existing plans and projects affecting the same area (SEA and appropriate assessment where available). The appropriate assessment carried out on these plans may also determine the scope for the appropriate assessment of individual components of the plan (projects) in terms of their cumulative effects. For example, when scoping the appropriate assessment of a mineral extraction plan, it may be useful to determine the range or extent to which the wider network of access roads to extraction sites may contribute to the cumulative impacts, e.g. in relation to habitat fragmentation affecting populations of species. Table 3 illustrates the sources that can provide information on other plans and projects that can give rise to cumulative effects. Tools to collate cumulative impacts, like databases recording the projects and plans to be considered, are helpful to streamline the assessment of cumulative effects. For instance, getting an overview of different activities is greatly facilitated if there is an up-to-date national or regional database, preferably including a dynamic map, which enables users to search all projects, including those still in the planning phase. In order for those databases to be useful for the appropriate assessment, competent authorities should aim to maintain the relevant documents online (e.g. impact assessment, mitigation measures introduced or conditions set for approval) also after permits are granted. Competent authorities (nature conservation, sectoral) should be consulted in order to collect information about the other plans/projects that should be considered during the assessment. Competent authorities can also contribute or support the assessment of cumulative impacts, as they have the best overview and knowledge about other activities across wider areas. They can also collect all relevant information and provide this to the project developers and consultants. The assessment of cumulative impacts may draw on information from a variety of sources including environmental studies and programmes, strategic, sectoral, and regional environmental assessments, project level environmental assessments, cumulative impact assessments from similar situations and targeted studies on specific issues. Expert advice can also be a good source of information on cumulative effects. A wide variety of methods and tools can be used to assess cumulative impacts, which usually also includes a scoping and an evaluation phase (see Figure 2 below). Consultations, checklists, overlay maps, network and systems analysis can be suitable tools in the scoping exercise, which will identify the potential impacts to be looked at further in the cumulative impacts assessment. Network and systems analyses are based on the concept that there are links and interaction pathways between individual features of the environment, and that when one element is specifically affected, it will also have an effect on other features that interact with it. Spatial analyses use geographical information systems (GIS) and overlay maps to identify where the cumulative impacts of a number of different actions may occur, and identify impact interactions. It can also overlay a project’s effect on selected receptors, features or resources to identify where the impact would be greatest. Sensitivity mapping can also be useful, as it may help predict potential cumulative impacts of certain activities on natural features that are vulnerable to the effects of those activities (see further details in section 4.2.2 of this guidance document) (31). Expert panels can be formed to identify and assess cumulative impacts. Matrices can be used to evaluate impacts and to consider the cumulative impacts of multiple actions on a site or feature as well as interactions between impacts. Modelling provides an analytical tool to quantify cause-and-effect relationships by simulating environmental conditions. This can range from air quality or noise modelling, to the use of a model representing a complex natural system. Carrying capacity (32) analyses look at the accumulation of impacts against thresholds. However it may not always be possible to set the threshold or carrying capacity for a particular feature or receptor. Whatever methods are chosen, they should be adjusted to the information available for the analysis and provide, whenever possible, a quantitative estimate of cumulative impact. If qualitative estimates of cumulative impact are to be developed, they should be based on a consensual estimate of a panel of independent experts rather than on the opinion of an individual expert. A panel may also be useful and even necessary, for instance where cumulative effects to be assessed come from different projects, e.g. hydropower construction, dredging and irrigation on the same river. The method chosen does not need to be complex. The aim should be to present the results in a way that can be easily understood by the developer, decision-maker (i.e. competent authority) and the public. Governments can play a significant role by providing and implementing enabling frameworks to guide this work and help identify and manage cumulative impacts. Box 11 sets out an example of a step-by-step process for cumulative impact assessment. The process must be applied in a flexible way, i.e. the steps can be taken out of sequence and may need to be implemented iteratively, with some steps revisited in response to the results of others.
Source: EUR-Lex (Cellar) · retrieved 2026-09-25 · Text as adopted (Official Journal); later amendments are not incorporated in this text.