Human water use is having an increasingly significant impact on both low and high water levels in the Rhine
Researchers from Deltares and Wageningen University & Research have taken an important step towards better understanding the impact of human water use on the flow of the Rhine. By incorporating water abstractions for industry, households, agriculture and livestock farming into a high-resolution hydrological model, they have demonstrated that human activity has a noticeable impact on both low-water and high-water conditions. The results have been published in Water Resources Research.
Water use in the Rhine
The Rhine is a major river in Europe in terms of drinking water, shipping, agriculture, industry and nature. Pressure on available water resources is increasing due to climate change, drought and growing water demand. In the study, the existing hydrological model for the Rhine was expanded to include abstractions of surface water and groundwater, as well as the return of used water to rivers. This provides a realistic picture of how human activities influence water discharge.
Water use and high water levels
Including water use also leads to more accurate simulations of high-water peaks in the Rhine and its major tributaries. Water abstractions reduce the amount of water that flows off immediately during wet periods, meaning that the calculated peak discharges are lower and closer to the measured values. Particularly downstream, where the effects of abstractions accumulate, this significantly improves the simulation of high water levels.
This finding is therefore relevant to public authorities and water managers working on flood protection. By taking human water use into account, future flood forecasts can be made more reliable.
Effects on low water levels
The research also shows that the effects of water abstraction on low water situations are less clear-cut. On the one hand, water abstraction for irrigation reduces the volume of water in the Rhine and thus lowers the discharge; on the other hand, industrial water abstraction can increase the volume of water in the Rhine and thus increase the discharge. This depends on the percentage of treated wastewater and cooling water that is returned to the river. However, reliable data on this subject is often lacking, both in the Netherlands and in the other countries within the Rhine catchment area. As a result, simulated extreme low-water conditions may be overestimated. This is particularly relevant for the Netherlands, as the terminus of the Rhine. Low Rhine discharge rates have direct consequences for inland waterway transport, drinking water abstraction, agriculture and nature. Data on water use and return are therefore becoming increasingly important.
Climate change and human water use are intertwined. Reduced melt water from Alpine regions, higher evaporation and increasing water demand will further increase the pressure on the Rhine. To properly assess future risks, hydrological models must therefore not only simulate natural processes but also take into account how people use water and return it to the system.
Better recording of water abstraction and return flows is needed
According to the researchers, the greatest challenge therefore lies not in the modelling itself, but in the lack of detailed data on water abstraction and return flows. These data are essential, particularly for drought and low-water analyses. Better records of water use contribute to more reliable predictions and better water management.
This research was carried out as part of the STARS4Water project, in which Deltares is collaborating with various European partners. In this project, we are seeking to gain a better understanding of the consequences of climate change for freshwater availability and the potential impacts on ecosystems, society and the economy within river basins.
