WW-I-1: Groundwater level

The picture shows a groundwater measuring point in the landscape. A nozzle protrudes from a round red base.Click to enlarge
A widely installed groundwater network provides regular data on groundwater levels.
Source: Photograph: © Christiana Mühlner

2019 Monitoring Report on the German Strategy for Adaptation to Climate Change

Table of Contents

 

WW-I-1: Groundwater level

Compared to the long-term mean, the frequency of months with low groundwater levels below-average is on the increase. In particular, precipitation deficits occurring several years in a row, lead to falling groundwater levels or reduced spring flows.

The column graph above the 0-axis shows the mean number of months in which the mean highest groundwater level or the mean highest spring discharge has been exceeded since 1961. The trend analysis was carried out for the time series from 1971 onwards, as the full set of measuring points is only available from then on. There is no significant trend, the development is cyclical. Below the 0-axis, the undershoot of the mean lowest groundwater level or the mean lowest spring discharge is plotted from 1961 onward
WW-I-1: Groundwater level

The column graph above the 0-axis shows the mean number of months in which the mean highest groundwater level or the mean highest spring discharge has been exceeded since 1961. The trend analysis was carried out for the time series from 1971 onwards, as the full set of measuring points is only available from then on. There is no significant trend, the development is cyclical. Below the 0-axis, the undershoot of the mean lowest groundwater level or the mean lowest spring discharge is plotted from 1961 onwards. Here there is a significantly increasing trend towards a larger number of months with undershoots.

Source: Groundwater monitoring networks of federal states
 

Increased occurrence of low groundwater levels

The extent to which groundwater can replenish itself in a location and the amount of groundwater levels that can develop, are dependent on a variety of influencing variables. Some of these variables include the distance between the aquifer from the top of the ground surface, the characteristics of the upper layers above the aquifer, the size and shape of rock cavities and the subterranean in- and outflow of groundwater. Above all, it must be remembered that the groundwater formation in any area is dependent on precipitation and surface run-off as well as evaporation. If the climatic conditions change, this will affect the formation of groundwater.

Rising temperatures act as triggers for a potentially higher evaporation overall, which means that less water will trickle down to infiltrate the groundwater. Years with lower total precipitation do not immediately affect groundwater levels. Contrary to surface water, groundwater reacts rather slowly to any changes in the precipitation regime. The situation can escalate in areas where in future, the availability of water will be restricted – on one hand owing to decreasing precipitation and on the other owing to an increased evaporation demand of the atmosphere. Both, changes in temperature and in precipitation affect the surface run-off, with knock-on effects on the groundwater. Although precipitation amounts increase in the winter months, the precipitation tends to fall on saturated or frozen ground and therefore cannot seep in. In the summer months, soils tend to dry out more owing to higher temperatures and lower amounts of precipitation. Precipitation which in future may more frequently occur as heavy rain, can either not or barely be absorbed by dry soil, thus trickling away largely above the surface.

In order to obtain an overview of the development of groundwater levels in Germany, 136 groundwater measuring points and spring flow points were selected across all federal states and hydrogeological environments, for which data are available from 1971 onwards; in respect of 96 measuring points the observation time series even date back as far as 1961. All these measuring points are in the uppermost aquifers and they are, as far as possible, unaffected by anthropogenic influences. In other words, there is no groundwater abstraction or irrigation taking place, the degree of soil sealing is low and there have been few changes in land management in the area. This makes it possible, to a considerable extent, to make connections between any changes observed at these measuring points and changes in the temperature and precipitation regimes.

Looking at the entire time series, it becomes clear, as shown by the mean value of all measuring points observed, especially in the course of the past decade, that there has been an increase in the occurrence of extremely low groundwater levels and very little spring flow. The number of months per year in 1971 to 2000 in which the mean of lowest groundwater levels or spring flows measured were not reached, has increased significantly since 1961. At the same time, the number of months in which the mean of the highest groundwater levels or spring flows measured long-term were exceeded, has decreased. Statistically speaking, however, this trend is not significant. It is also evident that owing to weather conditions there were cyclical changes in groundwater levels at least as late as the 1990s. Such changes can no longer be found to the same degree since the 1990s.

Developments vary across Germany even though the patterns show similarities. A particularly strong trend can be seen towards low groundwater levels in the low-precipitation areas of north-east Germany, i.e. in areas where annual precipitation amounts to less than 700mm. This situation prevails especially in Brandenburg, Sachsen-Anhalt and Mecklenburg-Vorpommern. However, even in regions with particularly high precipitation (annual precipitation of more than 900mm), i.e. in the uplands and in the alpine regions, it can be said that groundwater levels were clearly low. These findings would seem to require further research. Groundwater levels and spring flows were conspicuously low in the years 2013 to 2017. In view of a distinctly dry period, the data for 2018 point to the likelihood of a similar, presumably even more extreme situation arising.

In Germany also three quarters of drinking water is abstracted from groundwater. The formation of adequate volumes of high-grade groundwater is therefore a fundamental requirement for a sustainable supply of drinking water, also and especially in times of climate change. In the DAS Monitoring Report for 2015, just under 96% of groundwater bodies were found to contain satisfactory volumes of water, i.e. the formation of groundwater was found to be in balance with the extent of groundwater abstraction.

 

Interfaces

WW-I-2: Mean run-off

WW-I-4: Low water

BO-I-1: Soil moisture levels in farmland soil

 

Objectives

Groundwater management in a way to ensure the prevention of a deterioration in the volumes available and to ensure that satisfactory volumes are maintained or achieved (WHG §47 (1)).

Promoting decentralised infiltration of precipitation in order to contribute to the formation of groundwater; making increased use of spatial planning to safeguard water resources and using planning processes to aim for adapted consumption of water at a time of diminishing formation rates of groundwater (DAS, ch. 3.2.14).

Demand management as well as application of technological methods and improvements for a more efficient use of water, in order to avoid, at times of extended and more frequent regional drought phases and low-water periods, regional conflicts of use […] in respect of groundwater extraction close to the surface (DAS, ch. 3.2.3).