2023

Frederiek Sperna Weiland: "According to all scenarios, the Meuse will be lower in the summer"

How much water will flow through the Meuse during the different seasons in the future? Deltaresinvestigated this based on the KNMI 2023 climate scenarios. All scenarios show that less water can be expected in the summer. Frederiek Sperna Weiland of Deltares explains further. 

By the end of this century, between 10% and 30% less water is expected to flow through the Meuse in summer than now. This is according to research by Frederiek Sperna Weiland, senior adviser on climate change analysis in flooding, drought and water availability.

Last year, the Royal Netherlands Meteorological Institute (KNMI) released the 2023 climate scenarios. In them, KNMI translated the findings of the sixth report of the Intergovernmental Panel on Climate Change (IPCC) for the years 2050, 2100 and 2150 to the Netherlands.

Deltares then used the KNMI scenarios to analyse what this means for the flow regime of the Meuse and Rhine at these dates, the amount of water flowing through the river by season. The study was commissioned by the Ministry of Infrastructure and Water and conducted jointly with KNMI and Rijkswaterstaat. Frederiek Sperna Weiland led the research on these national flow scenarios, as in 2014, when KNMI's 2014 climate scenarios came out after the fifth IPCC report was published.

Wet or dry

The Meuse and Rhine are the most important rivers for the Netherlands, she says. "We therefore wanted to know: how are these flow rates going to change according to the new climate scenarios? And secondly, how do those changes compare to what we had previously determined with KNMI '14?"

The main conclusion of the sixth IPCC report is that we are starting to see changes all over the world owing to climate change. She summarises: "It's very likely going to get drier in many parts of the world. Like in the southern half of Europe."

The Netherlands is a bit in the middle in this respect: it is less clear whether it will become drier or wetter here. "This gives an extra incentive to do an analysis specifically for the Meuse and the Rhine," she considers.

Soil and plants

Researchers at Deltares looked at changes in the entire Meuse river basin upstream of the Dutch border in France, Luxembourg and Belgium to determine how much water enters the Netherlands. "KNMI determined the temperature and precipitation, and we then used our water models to investigate what that means for both rivers," explains Sperna Weiland. "In the results, we see that the increase in winter precipitation causes an increase in the flow rate of the Meuse in winter. But the decrease in summer precipitation and the fact that precipitation falls more as heavy showers will make the low-water flow even lower. This is not helped by the fact that temperatures are rising, causing more water to evaporate in the river basin." 

Into these hydrological computer models, the researchers put all the characteristics of these two rivers and their tributaries: data on soils, vegetation, the river network and how that affects water availability. In doing so, they looked only at the impact of climate change: how does precipitation and therefore the supply of water change? "The influence of human activities has not yet been included in this study," says Sperna Weiland. "Changing water use upstream and in the Netherlands, and modified barrage management will also affect the lowest flow rates and could turn out both positive and negative for the Netherlands."

Photo 2: Frederiek Sperna Weiland, Senior Adviser at Deltares.

Low and high water

The main difference between the Rhine and the Meuse is that, unlike the Meuse, the Rhine flows partly through high mountains, with snow and glaciers, says Sperna Weiland. "In the Rhine, we are going to see a lot of change as temperatures start to rise. As a result, there is less meltwater flowing through the Rhine from the Alps into the Netherlands."

She adds that the Meuse is a rain river and here the flow is directly affected by the amount of rainfall in the river basin. "A prolonged dry period greatly affects the flow rate in the Meuse, especially when dry periods occur more frequently in succession and last longer. This is because less groundwater flows out into the river basin."

The researchers looked not only at low water due to drought but also at high water – as it rains heavily, how often and to what extent floods occur change too. They are still calculating the impact on the amount of water in the rivers, including the evaluation of dyke heights. 

Much or little CO2

Deltares works with a total of six CO2 emission scenarios from the KNMI: one is low, one medium and one high – for each scenario there is a dry and a wet variant. If emissions are low, a high level of sustainability has been achieved, and if emissions are high, only a low level.

The latest scenarios assume little change in the Meuse in terms of average annual flow. But in summer, things are different. Sperna Weiland: "In all scenarios, the weekly flow goes down in summer. The models agree that it will become drier in summer anyway."

10-30% less

Under the high emission scenario, and the dry variant of it, the researchers expect that in a week with low water relative to the current situation, almost 30% less water will flow through the Meuse by the end of this century (see Figure 11). The low emission scenario and the wet variant involve 5% less water. This is similar in the Rhine. But it might even go down a little more there: around 35%.

Figure 2: Expected relative change of 7-day minimum flow in Meuse. 

In the 2014 KNMI climate scenarios, there were still a number of scenarios that assumed that it might get wetter and there would be a small increase in the Meuse flow rate. But in addition, the idea was that summers would be even drier than current forecasts and even less water would flow through the Meuse. "In that sense, it's a windfall for the Meuse that it is unlikely to get that much drier," says Sperna Weiland. 

Drinking water, agriculture, shipping

What are the consequences of less water flowing through the Meuse in summer? "The pressure on the water will rise," responds Sperna Weiland. "That applies to drinking water, agriculture, shipping and other sectors. When there are long periods with low flow rates, we really start to notice problems."

According to the 2023 KNMI climate scenarios, heat waves will also become more frequent and more severe in the Netherlands in the future. These changes in high temperatures are also included in the hydrological modelling and cause an increase in evaporation and a further reduction in the flow.

Water quality

How long can those periods of low water last? What exactly will be the impact for all these sectors that use water? And what are the actual implications for water quality? These essential questions will be further investigated in the National Water Model of the DELTA programme of the Ministry of Infrastructure and Water Management.

Sperna Weiland: "Less water will obviously have no positive impact in any event: the water becomes more concentrated, pollutants less diluted and the water temperature goes up. As a result, the oxygen in the water decreases. That is not good for the ecology, for the fish and plants."

Drying up

In Italy, the River Po completely dried up in 2023. Will it get as bad for us in the coming decades - is this a scenario we should consider for the Meuse too? "Of course, the Meuse, like the Po, is highly dependent on precipitation," Sperna Weiland responds. "But there is definitely a difference between southern and northern Europe. In the south, it is probably going to be drier than where we are."

She also mentions the fact that there is a treaty on the distribution of water between the Netherlands and Flanders, which clarifies the distribution of water brought from Wallonia and shared between the Netherlands and Flanders. "There are reservoirs upstream to keep the water level up in the rivers. In short, I'm not very afraid that the Meuse will run completely dry." 

International cooperation

She points to the increasing importance of such international agreements and treaties to ensure that countries in the Meuse river basin also take into the account the interests of other countries in their water management and help ensure a minimum flow rate. It is important to consider the interests of different sectors.  "Reservoir management in Wallonia and Germany can potentially contribute to a basic flow in the Meuse, and with good international agreements on water use, we can use water optimally and as sustainably as possible. This international coordination calls for further international research and more cooperation."