Meteorological droughts are characterised by below-average precipitation (precipitation deficits) over several weeks to months. This is due to persistent areas of high pressure that keep out moist air masses.
- Agricultural drought (soil moisture deficit)
If there is no precipitation for an extended period of time, the soil moisture also decreases. This means that less water is available for plants. In the summer half-year, the reduced soil moisture is often a result of a combination of low rainfall and high evaporation due to high temperatures. This is the case, for example, when a dry winter is followed by a spring with little precipitation and then periods of heat in the summer months.
- Hydrological drought (discharge deficit)
When the water level in rivers, lakes and groundwater falls far below the long-term average, this is referred to as hydrological drought. This situation is exacerbated by increased water abstraction, e.g. for irrigation.
- Socio-economic and ecological drought (supply deficit)
If the water demand of the population and the economy is higher than the available supply, this is referred to as socio-economic drought. If the water needs of the ecology can no longer be met, this is called an ecological drought.
What all these types of drought have in common is that there is not enough water available in an area over an extended period of time to meet the current water demand. However, exactly how much is 'enough' varies depending on the sector and population concerned. In a given region, the soil may already be very dry, affecting agricultural production. However, there may still be enough water left in the bodies of water of the same region so that fishing and water ecology are not (yet) affected.
Who is affected by drought?
The following areas can be negatively affected by drought:
- Drinking water supply: Some sources of drinking water may dry up. Moreover, supply bottlenecks may occur and thus conflicts of use between the drinking water supply and other uses (e.g. irrigation in agriculture). The supply of extinguishing water may also be affected. This is especially important because the risk of forest fires increases in dry weather.
- Energy supply/electricity sector: When rivers carry less water due to drought, run-of-river hydro power plants are not able to produce as much electricity. Storage power plants also produce less electricity due to the low reservoir levels. When water levels are low, bodies of water warm up more quickly. Cooling water for nuclear power plants, which is normally taken from rivers, is then too warm. Moreover, river water heats up further due to the operation of the nuclear power plants.
- Agriculture: Heat and drought lead to a rapid decrease in soil moisture. This damages plants and leads to crop losses or even crop failures (due to drying out, emergency harvests from insufficiently developed seeds, plant diseases, etc.). If there is no rainfall, dry soils can be irrigated. This causes the (ground) water level to drop, however. This is not always sustainable and can lead to further problems, especially if the water level is already very low due to drought. In the worst-case scenario, farms are forced to slaughter livestock because the livestock can no longer be supplied with sufficient feed without additional feed purchases or because there is no longer enough drinking water available. This affects alpine farms in particular. Crop and livestock losses not only have an impact on producers, but also on consumers: If the food supply becomes scarcer, prices rise.
- Forestry: Trees react stressed to a lack of water and are weakened as a result. They grow more slowly and produce less fruit or none at all. Prolonged drought can cause leaves to change colour or can cause trees to shed leaves or needles prematurely. Weakened trees are also more susceptible to insect infestation, e.g. bark beetles. Drought can lead to the death of treetops or entire trees. Falling branches or falling trees can then be dangerous for visitors to the forest. Trees then also no longer offer protection against natural hazards (protection forest). Drought also increases the risk of forest fires, given that more combustible material (fuel) is available.
- Ship traffic/transport: Passenger and freight shipping is negatively affected by low water levels. This also applies to leisure traffic on the waterway network, which can no longer take place regularly. Transport shipping on the Rhine, which is important for the import and export of goods to and from Switzerland, can be severely impaired by low water levels (reduced speed and/or loading capacity) and, in the worst case, must be suspended. This has an impact on commerce and can affect the national economic supply (e.g. shortages of animal feed, edible oils/fats, fuels).
- Nature/ecosystems/biodiversity: Various ecosystems are affected by drought, sometimes severely. For some species, the situation is even life-threatening. Water-dependent ecosystems and forests suffer especially severely from long periods of drought. Drought causes water levels to fall and water temperatures to rise, which reduces the oxygen content in the water and concentrates any pollutants the water may contain. These factors put fish under stress and can cause fish to die off. Tree mortality increases. This not only threatens biodiversity, but also human beings and their basic resources/material assets, e.g. through forest fires or weakened protection forests. Nitrate/pesticide inputs into the groundwater – especially from agriculture – are diluted less during droughts. Similarly, discharged waste water is also diluted less.
- Population: In general, droughts lead to a decline in water reserves (low water in lakes, rivers and groundwater reservoirs). In some cases, this can lead to water shortages in households. Where shortages are severe, communes may call for restrictions on water use (e.g. no watering of gardens and lawns, no washing of cars). In the event of water shortages, conflicts can arise between different users and interest groups with regard to who is allowed to consume how much water. Dry vegetation increases the risk of forest, field and bush fires. In populated areas, this creates a risk of injury to persons and damage to property. If many fires occur at the same time, there may be a shortage of available resources (fire engines, helicopters, firefighters). If there is heavy rainfall after a drought, local flooding may occur. The dried-out soil cannot absorb the water quickly enough, and large surface runoffs occur.