Excessively low groundwater levels pose a threat to many functions. In terms of the natural environment, they entail the risk of irreversible damage, whereby wetter target species disappear, and drier target species cannot reach the area. Farms may suffer drought damage and the probability of natural fires is increasing. Excessively low groundwater levels in the growing season prevent crops from securing their own water supply, in which case the demand for irrigation water from surface water and groundwater will increase substantially. If no such water is available, agricultural drought damage may ensue.
Which areas are particularly vulnerable to low groundwater levels?
In peat grassland areas, groundwater levels are closely monitored, because excessively low groundwater levels will lead to peat oxidation, resulting in soil subsidence. For cities, groundwater levels are relevant in relation to damage processes ensuing from excessively low groundwater levels – for example, cracks forming in roads, buildings, and subsoil infrastructure as a result of subsidence; rotting of wooden foundations; and dehydration of community parks and gardens.
Which unit is used in groundwater management?
A commonly used unit in groundwater management is the Mean Lowest Groundwater Level (MLGL): a calculated value indicating the depth to which the groundwater level in an area can sink. The MLGL is calculated as the average of the three lowest observed or calculated groundwater levels per annum (LG3), based on the values on the 14th and 28th of the month, for a minimum of eight years. Such low groundwater levels usually occur at the end of the summer season. In extremely dry years, the groundwater levels at many locations may sink deeper than the MLGL. Rather than the MLGL, the lowest groundwater levels (LG3) in a specific extremely dry year such as 1976 would provide a better picture of the impact of an extremely dry year on groundwater levels. In the Viewer tool, the extremely dry year is modelled on the year 1976, in which the precipitation deficits were slightly larger than those in the year 2018.
What does the map show?
Lowest groundwater level average year
The maps left of the bar reflect the lowest groundwater levels in the current situation. The maps to the right show the changes that may occur around 2050 as a result of climate change, sea-level rise, soil subsidence, and economic developments. Use the tabs to navigate between average years and extremely dry years.
The maps are outcomes of calculations based on the National Water Model , which have been used to determine the effects of the Delta Scenarios. These are combinations of the KNMI’14 climate scenarios and scenarios pertaining to socio-economic trends in the Netherlands (WLO ’15). The socio-economic developments are reflected in differences in land use and water consumption. The comparison map has been compiled by setting the outcomes of the 2050 Delta Scenario “Warm 2050” (combination of the warm, driest KNMI’14 climate scenario (WH) and the WLO scenario featuring low economic growth) alongside the current situation. More information on the National Water Model, on the basic forecasts, and on the background of the Delta Scenarios is available here .
Mean Lowest Groundwater Level
The “current situation” map shows that in the low-lying parts of the Netherlands, the MLGL lies relatively close to the surface level. At the elevated sandy soils, in the dunes, and in South Limburg, the MLGL is situated relatively deep below the surface level. The MLGL of urban areas in the low-lying parts of the Netherlands is generally lower than the MLGL in surrounding rural areas. This can be attributed to artificial raising and drainage. The comparison map shows which changes may occur by 2050. In large parts of the Netherlands, the mean lowest groundwater levels are declining, particularly in the north, in peat grassland areas, and along the rivers.
However, in small parts of the elevated sandy soils and in the dunes, the MLGL is rising. With respect to the elevated sandy soils, such a rise ensues from the increase in the annual precipitation surplus, which is caused by an increase in winter precipitation. As the groundwater level of these areas lies far below the surface, the expected increase in evaporation will have less of an impact on the groundwater levels. In the dunes, the rising sea level may raise the groundwater levels. This may have a negative impact on the local freshwater lens.
The lowest groundwater level in extremely dry years
In both areas featuring level-driven drainage and areas with gravity-driven drainage, groundwater levels in extremely dry years are markedly lower than the average values. This indicates that even in the current situation, we need to reckon with considerable dynamics in average groundwater levels over a range of years. In the future, these dynamics may increase even further as a result of climate change and socio-economic developments.
The expected change in groundwater level in extremely dry years is less than the average over a prolonged period of time. This is because a climate scenario will have less of an impact in a situation featuring deeper groundwater levels and low soil moisture content.
How can this information be used?
The maps show that by 2050, large parts of the Netherlands may be faced with lower mean lowest groundwater levels compared to the current situation. In the winter months, the groundwater level may rise as a result of increased precipitation in the winter season. See the MHGL map in the Climate Impact Atlas for details. Ergo, groundwater level dynamics will be increasing over the year. This is what adaptation efforts will need to focus on.
The groundwater maps are based on model calculations involving 250 m x 250 m cells, uniformly characterised to the best possible extent. This has generated nationwide, sound pictures for the current and future situations. However, the results cannot be used to underpin general local-level statements; this requires more detailed models that factor in local variations in, e.g., land use and surface-level altitude.
