Drought: what is it?

The term drought usually refers to an episode of lack of water more or less long but sufficient for the soils, flora and fauna to be affected. This phenomenon can be cyclical or exceptional and can affect a localized area such as an entire subcontinent. And while some areas are more vulnerable, droughts can strike almost anywhere on the globe.

Depending on the regions of the world and their water resources, the definition of the state of drought varies. In France, we consider that there is absolute drought when there is no drop of rain (less than 0.2 millimeters per day) for 15 consecutive days. In Australia, on the other hand, the state of drought is declared when an area receives less than 10% of precipitation compared to the average. annual.

There are three types of drought depending on the situation:

• meteorological or atmospheric drought which is linked to the shortage of precipitation over a given period;
• agricultural drought, which is a function of the humidity level of the soil at a depth of one meter. This drought depends on rainfall, but also on the nature of the soil, cultivation practices and the type of plant. This type of drought has significant effects on the vegetation;
• hydrological drought which occurs when soil water reserves (aquifers) and streams fall below average. This may be due to a particularly long and intense meteorological drought, but also to an overexploitation of water resources.

Causes and consequences of drought

The cause of a drought can be a lack of precipitation in winter or spring. It is indeed at this time that the water reserves fill up. A weather report “unfavorable” can also occur when anticyclonic conditions prevent precipitation. Just like high temperatures which promote the evapotranspiration of plants or poor management of resources by humans.

Note that the global warming has the effect of expanding drought-prone areas and enhancing the intensity and duration droughts in certain regions of the globe: in Africa, in the north of Latin America, in North America or even in the south of Eurasia in particular.

A persistent drought can ruin the agricultural production of a region, reduce hydroelectric production, lead to fires in meadows or forests, stop river navigation, disturb the fauna which no longer finds enough to drink, cause drinking water shortages and even, in extreme cases, trigger an exodus or a health crisis.