Droughts

Drought can be defined as a prolonged period of abnormally low rainfall, leading to a shortage of water over a specific region for a given period of time. Droughts are characterized by an deficit between water supply and demand, and can have important consequences for society, ecosystems, and agriculture. Understanding the different types of droughts and their complex dynamics is essential for implementing sustainable mitigation and adaptation strategies. Drought is more than just a lack of rainfall as this can propagate to a persistent shortage of surface water, soil moisture, and up to groundwater. For this reason, droughts are often classified into four main types different by their severity, impacts, and time scales:

Meteorological drought is often caused by short-term or prolonged precipitation deficiency. Climate variability, including phenomena such as El Niño and La Niña, can influence meteorological droughts. Impacts of meteorological droughts highly depend on timing and seasonality. For example, lack of rain during the sprouting phase in rain-fed agriculture could lead to crop failure.

Agricultural drought is a medium-term phenomenon, characterized by reduced soil moisture content and is caused by a prolonged period of meteorological drought. The lack of soil moisture can have a significant impact on crop growth. Statistical indices, such as the Palmer Drought Severity Index, help assess agricultural drought conditions.

Hydrological drought is characterized by lower streamflow, reduced water level in water bodies, and may also affect groundwater storage. These droughts are often influenced by factors such as reduced snowpack, increased evaporation, and human activities such as groundwater exploitation.

Socioeconomic drought encompasses the broader impacts of water scarcity on society, including water supply shortages, increased food prices, and social unrest.

The cascade between drought types is governed by the severity (i.e., magnitude), duration, and spatio-temporal distribution of drought events. Understanding drought dynamics is of pivotal importance to better assess drought risk and developed more informed adaptive strategies to mitigate impacts and build resilient societies under climate change conditions.