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Drought is one of the most serious natural phenomena that can have catastrophic consequences for the environment, agriculture, and economy. Simply put, it is a long-term shortage of rainfall, which leads to a disruption of the water balance. However, drought does not always look the same – we can distinguish four main types, which often occur one after another.
Atmospheric (meteorological) drought – the first warning signal
The first stage of drought is atmospheric drought – resulting from a long-term lack or negligible amount of atmospheric precipitation, the total amount of which is significantly below the average for a given region. Its characteristic features are a decrease in air humidity, an increase in average temperatures, and increased evapotranspiration – the process in which water evaporates both from the soil surface and through plant leaves. If such a situation persists for a longer period of time, it can lead to further, more serious effects, such as drying out of the soil or a decrease in groundwater levels.
Agricultural (soil) drought – a threat to crops
The second phase of drought is agricultural drought, also known as soil drought, during which there is a moisture deficit in the root zone of the soil. Such a deficiency negatively affects the condition of crops. Due to the lack of an adequate amount of water in the soil, the uptake of essential nutrients by plants is significantly limited. As a result, there is a decrease in the amount of harvested crops, and the harvest that can be collected may be of poorer quality. This is particularly dangerous for farmers, who may suffer large losses in crops. The best indicator of the occurrence of agricultural drought is the measurement of soil moisture. If its level drops below the critical value for a given type of crop, it means a transition to the second phase of drought. The time of occurrence of water deficit in the soil and its intensity depend directly on its retention properties. Due to the different types of soil, these parameters may vary both in time and space.
Hydrological drought – when rivers and lakes begin to disappear
The third phase is a consequence of long-term atmospheric and agricultural droughts. It is characterized by a significant decrease in the level of surface waters in both rivers and lakes, as well as retention reservoirs. It is also called a “hydrological low flow.” It occurs when the flow in rivers falls below the multi-year average flow. This is a period of reduced surface water resources in relation to the multi-year average value. Reduced surface water inflow leads to a decrease in the availability of water resources for many sectors of the economy. This is particularly reflected in industry and hydropower. Nevertheless, the greatest threat of hydrological drought is a significant reduction in access to drinking water for people and animals.
Hydrogeological drought – the most difficult to reverse
The most advanced stage of drought development is hydrogeological drought, characterized by a decrease in groundwater levels below the average values from previous years. It causes underground sources, including wells, to dry out. As a result, there are serious problems with water supply, which is particularly visible in areas that rely on underground intakes. Restoring groundwater resources is a long-term and complicated process, which is why this type of drought is particularly dangerous.
How to counteract drought?
In the face of the growing threat of drought, quick and comprehensive action is essential and crucial. Counteracting individual types of drought is invaluable in the context of climate change, which disrupts the familiar patterns related to the amount of rainfall and the retention capacity of soils in Poland.
The connections that occur between stages can teach us many things. Hence, emphasis is necessary on understanding and recognizing the subsequent phases of drought. Thanks to this, the relevant authorities will be able to develop effective strategies for managing water resources and focus on water retention in areas most at risk of drought from its first stages.
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