Hydrogeological drought and groundwater. Are we in danger of running out of water?

Hydrogeological drought is not the same as water scarcity, although the two often co-occur. It refers to changes in the position of the groundwater table, primarily in the shallowest aquifer, and can lead to deterioration of habitat conditions, disappearance of wetlands and drying up of shallow wells. Its proper interpretation requires distinguishing natural phenomena from the effects of anthropogenic pressure and taking into account the principles of groundwater monitoring.

Hydrogeological drought and hydrogeological low – are they the same thing?

More and more often in the popular science literature one can come across articles on groundwater issues in the broadest sense, which generally contributes to increased public awareness of the issue of hydrogeological drought and its consequences. Unfortunately, only some of these articles are written honestly and present the phenomenon of hydrogeological drought as something completely natural, not confusing it with water shortages.

Hydrogeological drought is a broader and more colloquial term, and in the scientific literature corresponds to the term hydrogeological low. The subject of monitoring the state of groundwater, and therefore, among other things, hydrogeological drought and lows, is dealt with in Poland by the National Geological Survey, which operates within the framework of the Polish Geological Institute (PIG-PIB).

According to the definition quoted here, a hydrogeological low is a time when there is less water than usual in the shallowest aquifer, which manifests itself as a deeper-than-usual position of the groundwater table (below certain conventional values).

Why is a hydrogeological low difficult to unambiguously capture?

This rather simple definition does not clarify the temporal aspect of the phenomenon. In its essence, a hydrogeological low is variable in time and space, which makes technical interpretation of the definition difficult. For example, a momentary lowering of the groundwater table at some specific location cannot be considered a low, because the values change both on a hydrological yearly basis and in multi-year cycles, and additionally react to the current meteorological situation.

The response itself is usually delayed. Intense precipitation or prolonged periods without rain affect the fluctuation of the groundwater table, but its effects may not be apparent until weeks or sometimes even months later. In some cases, this can lead to a simultaneous lowering of the groundwater table and the occurrence of flooding in an area.

Another difficulty in interpreting the phenomenon is brought by the spatial aspect. The state of the groundwater table and the dynamics of its fluctuations are greatly influenced by local geological and hydrogeological conditions, especially the type of rock in which the water is located.

How is the status of groundwater monitored?

Groundwater monitoring is carried out at points called piezometers. These are small-diameter holes that reach into the aquifer. In the past, the water level was measured in them manually, using an auger on a measuring tape, but today special instruments called diverters are used, which record the pressure of the water column above the sensor automatically. Based on these measurements, the position of the groundwater table can be precisely determined.

Points for observing groundwater levels in the context of analyzing low water phenomena are carefully selected. First of all, they should cover the shallowest aquifer and must not experience any apparent human influence artificially lowering the water level, such as through abstraction, which must additionally be confirmed by long-term observations.

The network of such authorized monitoring points varies over time. Currently, there are nearly 1,500 of them, distributed throughout the country and selected to be as representative as possible, while covering the area evenly.

However, the number of observation network points centered on the first groundwater level is much smaller, which means that in a regional low assessment, one point is responsible on average for representing more than 1,000 ^km2 of area. Of course, this is only a statistical statement, because, as the observation results show, the nearest points, even in the same aquifer, do not necessarily behave identically at all. On the other hand, similarities between the dynamics of water table fluctuations at more distant points are not at all unique.

Hydrogeological drought is not the same as water shortage

As can be seen from the above, drought – or hydrogeological low – is a natural phenomenon, but quite problematic to forecast. It is difficult to determine unequivocally when it begins and which moment to consider its end. It is also usually difficult to predict what area it will occupy.

However, it is known what its symptoms will be once it occurs. Since it affects the shallowest aquifer, it will be most easily recognized by longer sustained higher than usual water table depths in shallow farm wells, sometimes even leading to their drying up.

And this is a good time to explain another term – water shortage. We deal with groundwater shortages when there begins to be a shortage of resources to meet economic needs (for municipal, industrial or agricultural purposes). The two phenomena – hydrogeological drought and water shortages – are related, but to some extent remain independent.

If we are talking about drought in wetlands where there is no economic human activity, we should not use the term scarcity. On the other hand, it can be stated in areas where a hydrogeological drought or low currently does not occur – this will be the case, for example, in the area of a major groundwater intake or around an open pit mine, where there is a local artificially induced lowering of the groundwater table. They then begin to be in short supply, at least for agricultural or municipal purposes for individual farms that use the first groundwater level. Very often, however, both phenomena occur together and their effects overlap.

What are the effects of lowering groundwater levels?

When an area begins to run out of water for basic purposes, various temporary solutions are proposed. For example, supplying the local population with cisterns or restrictions on water use, i.e. watering bans, are introduced. Nature also suffers as a result of hydrogeological drought, especially so-called water-dependent ecosystems. The best examples are disappearing wetlands and drying up peatlands (the latter, once dried up, are virtually impossible to restore on a human time scale).

So, in the event of a hydrogeological drought, will we run out of drinking water nationwide? Certainly not, since most of Poland is supplied with water for municipal needs from deeper aquifers. However, there are and will continue to be local supply problems in the aforementioned areas.

Despite the rather optimistic conclusion at the end, let’s save water, especially groundwater – it is our most precious resource. Therefore, this year’s snowy winter should please us all. Snow cover is a very important part of the water cycle in nature, contributing extremely significantly to groundwater recharge.

Where to check the current hydrogeological situation in Poland?

As already mentioned, the fluctuation of groundwater levels in the monitoring network is carried out by the National Geological Survey. Each month , hydrogeological situation announcements and hydrogeological warnings are provided on www.pgi.gov.pl, under the tab Hydrogeological situation – current information.

The latest published analysis is for April 2026 and is based on data from 201 monitoring points capturing the first aquifer. Compared to the previous month, as many as 71 percent of the analyzed monitoring points saw a decrease in the average groundwater level, resulting in a deterioration of hydrogeological conditions over a significant area of the country. An increase in the groundwater table was recorded for 24 percent of the points, and no change was observed at 5 percent of the points.

The effect of reduced retention was to increase the area of areas at risk of hydrogeological lows compared to the situation in the previous month. Measurements by PSG show the continued existence of areas threatened by hydrogeological lows in the West Pomeranian/Pomeranian, Podlasie, Mazovian, Łódź and Świętokrzyskie provinces. New areas of hydrogeological low have appeared in the provinces of Łódź and Lublin.

Unfortunately, after the snowy winter, only a memory remains, and precipitation deficits during the spring months are adversely affecting forecasts in the following months. We should expect the maintenance/development of already existing and possibly the emergence of new areas of hydrogeological low risk.

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