Drought is a natural phenomenon characterized by a lack of water over a sufficiently long duration to impact soils and vegetation. A drought episode can be sporadic or cyclical and may have devastating consequences on the environment, agriculture, economy, and daily life. It occurs when precipitation is significantly below normal for an extended period, leading to a water deficit in soils and water reserves.
Drought is explained by a temporary rainfall deficit that is not unique to the climate of the affected area but lasts long enough to be harmful. Aridity, on the other hand, results from a low average precipitation coupled with high evapotranspiration. The lack of rain is a permanent feature of the region's climate, affecting areas with scarce rainfall and high temperatures.
- Meteorological Drought (or Atmospheric): It corresponds to excessively low rainfall over an extended period.
- Agricultural Drought : It occurs when the soil moisture content (at one meter deep) is too low to support good crop conditions. This type of drought occurs even with normal precipitation and depends on soil characteristics, agricultural practices, and the types of plants cultivated.
- Hydrological Drought: It occurs when the water levels in rivers significantly decrease, leading to a water shortage. Insufficient precipitation is one of the triggering factors for this type of drought, as well as soil permeability, which affects water infiltration and runoff capacity.
Water deficit and high temperatures are the primary causes of drought. Insufficient precipitation in winter and spring, combined with high temperatures, lead to increased evaporation and plant evapotranspiration, causing soil drying and erosion. Climate change tends to exacerbate these phenomena.
Excessive water consumption for human activities can worsen drought. When water reserves decrease due to unfavorable weather conditions, they are not always effectively managed by humans in their agricultural, industrial, and domestic operations. Overexploitation of water resources can lead to the depletion of groundwater and threaten its sustainability.
Globally, drought can affect any country with specific climatic conditions: decreased precipitation over a certain period accompanied by high temperatures. Some areas are more vulnerable than others, especially tropical and subtropical zones. Recent notable droughts include those in the Sahel, the Horn of Africa, Mexico, the northeast of Brazil, certain areas in China, India, and Russia, as well as Southeastern Europe.
- On Flora: Dry and dehydrated trees can die, increasing the risk of forest fires. Additionally, trees become vulnerable to cold temperatures for up to ten years after a drought.
- On Soils: Dried soils lose their ability to absorb precipitation correctly, leading to floods, inundations, and landslides.
- On Fauna: Lowering water levels in rivers affects the survival of fish and other animals that depend on them. Migrations become necessary, disrupting the ecosystem.
- For Humans: Vulnerable populations face risks of dehydration, famine, and epidemics during droughts. It also contributes to climate migrations and can lead to conflicts.
- On Agriculture: Water stress can reduce agricultural production and result in crop losses.
- On Drinking Water Supply: River, lake, river, and groundwater levels decrease, leading to water use restrictions for irrigation, domestic, and industrial purposes.
- On Water Quality: Water scarcity reduces the dilution of pollutants, increasing the risk of contamination in water reserves.
- On Electricity Production: During droughts, the availability of water for cooling nuclear power plants is reduced, potentially causing a decrease in electricity production.
To combat risks associated with drought, preventive measures and water reserve management are crucial. This involves eco-friendly practices for domestic consumption, more efficient irrigation methods in agriculture, water-efficient industrial procedures, and proactive management of water networks and resources for communities.
The most severe droughts in history have sometimes been linked to devastating famines and social upheavals. For instance, the 19th-century Great Irish Famine, exacerbated by a series of poor harvests due to drought conditions, resulted in the death of over a million people and the emigration of millions more.
This underscores the fact that drought, beyond its environmental effects, can have profoundly tragic consequences on human societies, highlighting the importance of water management, food security, and climate change adaptation to prevent such tragedies in the future.