The Phenomenon

Drought is a creeping phenomenon, with a slow onset and different definitions

Drought is a normal and recurrent feature of climate, which can virtually occur in all climatic zones and is related to the concept of temporary water deficit. Its impacts can vary from region to region, depending on its characteristics and water demand for several purposes.

Redmond (2002), in fact, defines drought as a “Condition of insufficient water to meet needs”. Drought differs from Aridity, the latter being a permanent feature of climate, occurring in areas characterized by a permanent water deficit due to lack of precipitation and high evapotranspiration.

Characteristics of Drought

Drought can have different impacts depending on its characteristics




Geographic extent


Slow onset

One rainfall doesn’t necessarily end a drought event.


Drought is not a simple physical phenomenon.
The cumulative effect of rainfall deficiency over time impacts differently on the society, being the result of the interaction between a natural hazard (precipitation reduction below the average) and water requirements for several uses.
For this reason often drought is identified in four types: meteorological, agricultural, hydrological and socio-economic (Wilhite, 2000).
Wilhite, D.A., 2000. “Drought as a natural hazard: concepts and definitions” in Drought: A Global Assessment, Volume I, D. A. Wilhite (ed.). Routledge, London, pp. 3-18.


Reduction of precipitation below the climatological average (at least 30 years), for a specified period (e.g. days, months, years) in a specified area.


Decreasing of water availability (due to rainfall shortage and increasing of evapotranspiration) in the root zone, that impacts on the optimal crop growth (specially in some critical phenological phases), causing the yields reduction.


Involves a reduction in water resources (streamflows, lake levels, groundwater, underground aquifers) below a specified level for a given period of time, due to a long-lasting precipitation reduction.


Socio-economic drought is associated with the supply/demand of water related to some economic goods and needs.
During particularly intense and extended droughts, water allocation for common human activities can be compromised.


The decreasing of water availability causes direct and indirect damages to ecosystems and anthropic activities

Agriculture is the first sector experiencing the negative effects of severe droughts that, if prolonged, can affect streamflows, lake levels, groundwater and underground aquifers, also involving natural ecosystems, and domestic and industrial sectors.
Moreover, water shortage is one of the factors triggering land degradation and desertification processes, and influencing the carbon sequestration capability of plants.

Why a Drought Climate Service