klimaatverandering gevolgen

Climate change and the consequences for water supplies in Europe

As temperatures rise and precipitation decreases due to climate change, the combination of heat and drought is becoming more common. This makes water shortages more likely: less water is available on the one hand, while water demand is increasing on the other. As global average temperatures rise, the risk of water scarcity is increasing from ‘moderate’ in the case of 1.5°C warming to ‘high’ in the case of 3°C warming in the West, and from ‘high’ to ‘very high’ in Southern Europe. This results in higher yield losses in agriculture, particularly in Southern Europe. According to the recent IPCC report[2], the drought frequency has already risen there. Adaptation measures to reduce agricultural damage include irrigation, changes to agricultural practices, different crops and moving out of high-risk areas. However, the possibilities for more irrigation are limited because of the decline in water availability in rivers, particularly in Southern Europe. In addition, the additional use of water for irrigation could actually exacerbate water shortages for other users. Other sectors are also being affected. Lower river discharges mean that less hydropower can be generated, there is less water for drinking water purposes, and shipping is hindered more often. The combination with higher temperatures reduces the availability of cooling water for industry, and leads to poorer water quality, with consequences in areas such as drinking water supplies and biodiversity.

The Netherlands

The rivers are an important source of fresh water for the Netherlands. Rhine water is used throughout the lower-lying areas of the country for agriculture, for nature and to maintain water levels in the ditches and polder-drainage canals (for example to prevent land subsidence and for infrastructure such as bridges and houses). In addition to these effects, it is becoming increasingly difficult to keep salt water out. Excessive salinity levels have negative effects on regional water management but also on drinking water intake on, for example, the Lek River, the Amsterdam-Rhine Canal and the Brielse Meer lake. Emergency measures are then required. An example of an emergency measure of this kind is the Climate-Resilient Water Supply for the Western Netherlands. Another example is limiting lock movements (at the IJmuiden sea locks, for example), with disruption to shipping as a result. Furthermore, at low discharges, water quality declines because nutrients, drug residues and chemicals are not diluted and because of higher temperatures. This means that drinking water companies have to work harder on treating water, and intake and discharge restrictions for industry become more likely. There is also a higher probability of intake being suspended temporarily if there is an isolated discharge of chemicals somewhere upstream.

klimaatverandering gevolgen
Impact of drought on society

Expectation for the Rhine basin, important source of fresh water

The Rhine is a mixed river type that is fed by both melt water from glaciers and snow, and precipitation. Climate change affects the discharge regime – the average discharge level through the year – in four ways (Figure 1):

  1. precipitation falls as rain rather than snow more often;
  2. glaciers retreat, and so the amount of melt water declines;
  3. the distribution of precipitation over the year changes, with more precipitation on average in winter and less in summer; and
  4. evapotranspiration increases in line with regional warming.

The disappearance of snow and ice, combined with reduced precipitation in summer, has a major impact on low-discharge events throughout the Rhine basin. The variation in the discharge regime seen in the different KNMI climate scenarios (see Figure 1) reflects the uncertainty in precipitation patterns that is affected by meteorological fluctuations. G stands for moderate warming, and W for high warming: 1.5°C and 3.5°C, respectively, by the end of this century. L, H, and dry stand for variations in high and low pressure areas, with Wh,dry being the driest scenario for the Rhine basin.

Average summer discharges of the Rhine at Lobith could fall to 1000 m3/s in the case of severe climate change. If a discharge level of this kind occurs, the National Water Allocation Committee comes into action, which is currently considered to represent an emergency. However, in the scenario with high warming (Wh-dry), this will be the average situation. If the glaciers also disappear in the future, average summer discharges will fall even further.

The frequency of extreme discharges is also increasing (Table 1). The duration of low Rhine discharges (the threshold used here is 1020 m3/s) doubles in the Wh-dry scenario, and falls slightly in the moderate scenario. The duration of extremely low discharges (700 m3/s) could even triple. The current Rhine discharge at Lobith was lower than 700 m3/s for more than a week without interruption this summer (Figure 2). In the past 120 years, the discharge has been this low for more than one week on three previous occasions: 1921, 1947, and 1949 (Figure 3). The Rhine at Lobith is now extremely low for an average of one day a year; this will be 13 days in the Wh-dry scenario.

klimaatverandering EU gevolgen figuur 1
Figure 1. Monthly mean discharge (discharge regime) of the Rhine in the KNMI’14 scenarios in the reference years 2050 (left) and 2085 (right) [3]. The black line shows the long-term average over the period 1951-2006, and the other lines show the averages for the five KNMI’14 scenarios.
klimaatverandering EU gevolgen figuur 2
Figure 2. Discharge over time at Lobith for a number of years in the past. The background colours represent zones from extremely high to extremely low on the basis of historical statistics. The grey dotted line shows the point at which the National Water Allocation Coordination Committee comes into action.
klimaatverandering EU gevolgen figuur 3
Figure 3 Frequency (repeat period in years) of the number of days with low Rhine discharge at Lobith below a threshold of 1020 m3/s (left-hand figure) and 700 m3/s (right-hand figure). The green and orange lines show the statistics for two different KNMI’14 climate scenarios in 2050 and 2085. The blue line shows the past. Please note: due to the limited length of the measurement series, the estimated repeat periods are uncertain in excess of 30 years.

Table 1: Duration (number of days) of a Rhine discharge at Lobith lower than 700 m3/s or 1020 m3/s in two specimen years and with different climate scenarios in the reference year 2085, at different repeat periods. The Rhine at Lobith is now extremely low (<700 m3/s) on one day a year on average; in the WH,dry scenario, this will be the case on 13 days in the reference year 2085. Please note: 1020 m3/s is the ‘Agreed Low Discharge’, the discharge level below which the river falls about 5% of the time and to which the guaranteed draught for shipping is linked.

klimaatverandering EU gevolgen tabel 1

What measures can we take?

To reduce the risk of water shortages, it is important to start using less water. In the Netherlands, however, we are seeing water demand increase as summers get drier and hotter (with higher drinking water consumption and irrigation) but also because of population growth and system interventions such as raising groundwater levels in peatland areas. Part of the increase in water demand is caused by more evapotranspiration, which can only be reduced to a limited extent. For Dutch agriculture, part of the solution involves irrigating more sparingly and the intelligent selection of crops that require less water or can cope with more brackish water. In the case of shipping, measures are being explored in the areas of infrastructure, the vessels themselves, logistics and information systems. We are also seeing water demand increase in the basin as a whole, as a result of which river discharges could fall further. International cooperation in the river basins is therefore essential in order to establish a shared picture of developments and in order to work together on solutions.

The low river discharges of recent months still qualify as an extreme event in the current climate but they may become more frequent in the future. Measures are needed to reduce water use and retain more water, not only in the Netherlands but also in the Rhine and Meuse basins. Adaptation measures can have a major impact on users, and time is needed to implement them. That is why we must begin now.

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