How can we adapt to climate change in the Rhine basin?
In a cross-boundary research project called ACER, we aim to identify how long term developments such as climate change, socio economic developments, spatial planning and policy developments influence water management in the Rhine basin. Within this context, the PhD research of Aline te Linde focuses on quantifying probabilities of the occurrence of future floods and droughts.
Upstream changes in the river basin can affect the amount of water reaching the Netherlands. The safety levels that are used to plan dike heights along the Rhine vary from 1/100 and 1/200 per year, up to 1/500 per year in the Lower Rhine and even 1/1250 per year in the Netherlands. With observed discharge time series of 120 years at most, statistical extrapolation is needed to estimate discharges occurring at those high safety standards. This results in large uncertainties when estimating design discharges and projecting shifts in safety levels due to climate change.
An innovative way of resampling precipitation and temperature data and implementing global climate change projections, creates time series describing the range of possible future river discharge scenarios of up to 10,000 years. This climate information is used within an integrated Rhine model to analyze the effect of climate change and adaptation strategies on discharges, return periods and waterlevels, with a focus on the German part of river Rhine.
After identifying long-term impacts, different water management strategies (for example dike heightening, bypasses, detention areas, land use change, potential damage reduction) are developed to cope with the impacts on flood risk. The strategies are targeted at areas in both Germany and the Netherlands and are developed with stakeholders from both countries in a series of workshops. Risk is defined here as probability multiplied by damage in case of a flood.
Results show that flood frequency is expected to increase due to climate change. The ongoing increase of urbanization along the Rhine in flood prone areas, adds to an increase of flood risk. Extra detention areas to mitigate extreme events, which were proposed by the stakeholders, are effective for discharge extremes with return period around 1/100 to 1/200 per year. In case of more extreme events, these detention areas will be flooded and therefore more robust strategies that combine different measures are being defined.
The answer on how to adapt to climate change in the Rhine basin will be sought in risk reduction. Basin wide and cross-boundary risk management is also enforced by the recently engaged EU Flood Directive. Work is ongoing on developing a basin wide risk model, where potential damage and projected future probabilities of flood occurrences are combined. Different strategies will be evaluated as to how they mitigate extreme events and lower risk.
ACER is funded by BSIK ‘Climate Changes Spatial Planning’.