What is drought?

Drought can be seen as a natural and temporary meteorological condition in which there is a significant reduction in rainfall compared to the average climatic conditions of the place in question, possibly accompanied by an increase in temperature that causes high rates of evapotranspiration (Drought Bulletin, ISPRA) .

This phenomenon has different characteristics in the different components of the hydrological cycle, which in turn produce different effects on water systems, crops and socio-economic and environmental systems.

In relation to the impacts produced and the processes involved, four categories of drought can be distinguished:

  • meteorological drought;
  • agricultural drought;
  • hydrological drought;
  • socioeconomic drought.

The discriminating factor that determines the transition from one type to another is the persistence of particular climatic conditions (deficit of rainfall, high temperatures, strong winds, etc.).

For periods of less than one year, there are effects on crop growth, due to the deficit of water supply to the soil. The prolongation of the rainfall deficit has effects on the flow of waterways. For periods longer than one year, there are negative impacts on the water availability in the groundwater (Mariani et al., 2018). Over time, these conditions also generate impacts on the socio-economic and environmental sector.

Sequence of drought phenomena and description of the impacts (WMO, 2006)


Dai (2011), Drought under global warming, Wires Climate Change, Vol. 2, Issue 1, 45-65

Mariani et al. (2018), Linee Guida sugli Indicatori di Siccità e Scarsità Idrica da utilizzare nelle Attività degli Osservatori Permanenti per gli Utilizzi Idrici, Stato Attuale e Prospettive Future, CReIAMO PA

Bollettino siccità, ISPRA: https://www.isprambiente.gov.it/pre_meteo/siccitas/index.html