Drought is a natural hazard triggered by a very significant decrease in precipitation, usually combined with rising temperatures and, consequently, increased evaporation, which can last for several months or even years. Droughts have environmental, social, and economic consequences, and their direct and indirect impacts are difficult to quantify.
Drought does not always manifest itself in the same way. Depending on its origin and impact, it may appear in different forms, which often interconnect and evolve from one to another. Understanding these types — from meteorological drought to hydrological and agricultural drought — is essential to grasp the entire cycle of water scarcity and to adopt effective prevention and mitigation measures.
Meteorological drought: drought associated with the absence of precipitation, defined as the deviation of precipitation from the average value of the climatological norm. This assessment is carried out by IPMA.
Hydrological drought is associated with storage levels in reservoirs, aquifers, and watercourses in general. This type of drought is usually out of phase with meteorological drought, as it takes a longer period to restore storage levels after rainfall returns. This assessment is carried out by APA.
By analysing the evolution of storage levels, it is possible to assess actual water availability and comparing it with historical series makes it possible to determine the possible occurrence of hydrological drought. Considering the significant hydrological differences across Portugal, identifying hydrological drought in each region does not mean that this drought exists across the entire national territory, nor that its severity is of the same magnitude.
Agricultural drought: drought associated with the lack of water caused by an imbalance between the water available in the soil, the water needs of crops, and plant transpiration.
Water scarcity is different from drought and results from water use in each region exceeding the available water resources. When drought events occur in a region already experiencing water scarcity, this situation becomes further aggravated.
