Human water use has a greater impact on low and high water levels in the Rhine than previously thought
The amount of water people take from rivers and groundwater has a greater impact on the Rhine than previously thought. Researchers at Wageningen University & Research (WUR) and Deltares show that human water use is an important factor behind both low and high water levels. By including human water use in an advanced hydrological model, the Wflow model, they examined its effect on river flows, providing a step toward better understanding these processes. Their findings have been published in Water Resources Research.
Human water use should be included in hydrological models
The river Rhine is crucial for drinking water, shipping, agriculture, industry and nature. At the same time, the river is under increasing pressure from climate change, drought and growing demand for water. For this study, first author Devi Purnamasari and her colleagues expanded an existing high-resolution hydrological model with existing data on water withdrawn from rivers and groundwater, as well as water returned to the river after use. This creates a more realistic picture of how human activities influence the flow of the river Rhine.
“Water management is no longer just about rainfall and meltwater. We know that the way people use water also has an impact. What makes our study unique is that, for the first time, we have been able to calculate what these local water abstractions mean at the scale of an entire river basin - in this case, the river Rhine,” says Ryan Teuling, co-author of the study. “The magnitude of the effect surprised us to some extent. Our results show that it can no longer be ignored.”
Better predictions of high water
The study shows that incorporating human water use into hydrological models leads to more accurate simulations of peak river flows in the river Rhine and its tributaries. This is because water withdrawals reduce the amount of water that runs off directly during wet periods, resulting in simulated peak discharges that more closely match observed conditions. The improvement is particularly noticeable downstream, where the effects of water use accumulate along the river.
These findings can help water managers improve flood forecasting and better prepare for future high-water events.
Also important during drought
The influence of human water use on low water levels is more complicated. Water taken for irrigation reduces river flows, while treated wastewater, cooling water from industry and irrigation water that does not evaporate can add water back into the river. Because reliable data on these return flows are often lacking, extreme low-water situations are still difficult to predict accurately. This is especially important for the Netherlands, where the river Rhine flows into the sea, and reliable forecasts are essential for shipping, drinking water supplies, agriculture and nature.
"Water managers need a clear picture of how human water use affects the Rhine, especially during droughts," says lead author Devi Purnamasari. "Evaluating the impacts on extreme low flows remains particularly difficult, as low flow conditions are highly sensitive to change. Meanwhile, the data we have is often aggregated over the year rather than reflecting how water use varies season to season. As pressure on water resources continues to grow because of climate change, having more detailed water abstraction data is becoming increasingly important for improving these models.”
Water management in a changing climate
Climate change is reducing the amount of meltwater from the Alps, increasing evaporation and driving up demand for freshwater. As a result, climate change and human water use are becoming more closely linked. According to the researchers, hydrological models should therefore not only represent natural processes but also take into account how people use water and return it to the system.
The biggest challenge is no longer the models themselves, but the availability of reliable data on water abstractions and return flows. Better registration of these processes is essential for improving predictions of future drought and flood risks.
“There is still a great deal of uncertainty around these processes,” says Ryan Teuling. “Our models suggest that, under the assumptions we currently use, low river discharge at Lobith could, somewhat paradoxically, have been even lower without water abstractions. That is a wake-up call for water management in the Netherlands and something that deserves further investigation.”
Bijdrage aan toekomstbestendig waterbeheer
These findings closely connect with WUR's research on sustainable water management. Researchers across Wageningen University & Research are studying how climate change, human water use and water systems interact. For example, they study how water moves through both natural and human-influenced landscapes, and how this knowledge can contribute to sustainable and resilient water management. They also develop models and new insights that help water managers respond to drought, flooding and the growing pressure on freshwater resources.
