Aarhus Universitets segl

No 479: The significance of climate change for the need for action for coastal waters

Timmermann, K., Stæhr, P.A.U., Göke, C. Upadhyay, S. & Erichsen. 2021. Klimaændringernes betydning for indsatsbehov til kystvande. Aarhus Universitet, DCE – Nationalt Center for Miljø og Energi, 30 s. - Videnskabelig rapport nr. 479. http://dce2.au.dk/pub/SR479.pdf


For coastal waters, nutrient reduction needs and target loads are determined based on current climatic conditions and ecological status of selected environmental indicators. Even though changes in climatic conditions may affect the environmental indicators, climate change and its potential impacts on environmental status and target loads has not been addressed. This report analyzes the potential role of climate changes since year 1900 for the estimated need for nutrient load reductions required to ensure at least good ecological status, which is the environmental objective for coastal water bodies under the Water Framework Directive (WFD).

The analysis is based on spatially distributed meteorological variables for wind, temperature and precipitation from around the year 1900. Models describing the condition of the environmental indicators “depth distribution of eelgrass” and “summer chlorophyll-a” is used to predict, the values of the indicators in a year 1900 climate. For eelgrass, the model results reveal that the depth limit of eelgrass in most water bodies would have been lower in a year 1900 climate compared to the current climate. Hence, the status values of the eelgrass indicator would have been lower if estimated in a year 1900 climate. For the chlorophyll-a indicator, the model results show higher chlorophyll-a concentrations in most water bodies in a historical climate compared to the current climate. Hence, the reference condition and environmental target for the chlorophyll-a indicator would have been higher if the target values were established using a year 1900 climate instead of the current climate.

The effects of climate change for the eelgrass and chlorophyll indicators have a contagious effect on the nutrient load reductions required for achieving good ecological status. Thus, based on the results, an additional effort of approximately 600 tonnes N / year, is expected if the status value for eelgrass was measured in a year 1900 climate compared to the current climate. Similarly, the need for nutrient reductions would be approximately 1500 tonnes N lower if the chlorophyll environmental target had been established based on the historical year 1900 climate instead of the current climate.