Drought is a slow-onset natural hazard that allows for the implementation of disaster risk reduction measures as requested by the Hyogo Framework for Action. In order for planners and the public to implement effective mitigation and preparedness measures to reduce drought impacts, they have to understand its evolution, complexity, social implications and people’s vulnerability. To this end, wide-ranging and well-coordinated efforts at international, regional, and national levels are needed to build drought-resilient communities and societies. 
Drought is a natural part of climate, although it may be erroneously considered as a rare and random event. It occurs in virtually all climatic zones, but its characteristics vary significantly from one region to another. Drought is a temporary aberration; it differs from aridity, which is restricted to low rainfall regions. 
Drought is categorized as a hydro-meteorological hazard. According to the UNISDR Terminology on Disaster Risk Reduction 2009, “hazard” is defined as “a dangerous phenomenon, substance, human activity or condition that may cause loss of life, injury or other health impacts, property damage, loss of livelihoods and services, social and economic disruption, or environmental damage”. In technical settings, hazards are often described quantitatively by the likely frequency of occurrence of different intensities for different areas, as determined from historical data or scientific analysis. 
A broad definition of drought is a deficiency of precipitation over an extended period of time, usually a season or more, which results in a water shortage for some activity, group, or environmental sectors. However, in terms of typologies, droughts are classified as meteorological, agricultural, hydrological, and socio-economic. 
Meteorological drought is a natural event that results from climatic causes, which differ from region to region. Agricultural, hydrological, and socio-economic drought, however, place greater emphasis on the human or social aspects of drought. They highlight the interaction between the natural characteristics of meteorological drought and human activities that depend on precipitation to provide adequate water supplies to meet societal and environmental demands.
Multilateral Environmental Agreements such as the United Nations Convention to Combat Desertification (UNCCD) and the United Nations Framework Convention on Climate Change (UNFCCC) are also strongly linked to some aspects of drought risk reduction framework and practices. The UNCCD has its specific definition of “drought” as “the naturally occurring phenomenon that exists when precipitation has been significantly below normal recorded levels, causing serious hydrological imbalances that adversely affect land resource production systems”.
The risk associated with drought for any region or group is a product of the exposure to the natural hazard and the vulnerability of the society to the event. The UNISDR definition for “vulnerability” is “the characteristics and circumstances of a community, system or asset that make it susceptible to the damaging effects of a hazard. Leaders and planners in drought-prone regions should conduct risk assessments to both better understand the drought hazard and identify the factors and processes concerning who and what is most at risk to drought, and why. 