Drought is a recurring climatic phenomenon characterized by a reduction in rainfall compared to the average considered normal, which tends to spread unevenly over time and space and causing the water available to be insufficient to meet different needs of both humans and the ecosystem (Ortega-Gaucin, 2013).
It is difficult to objectively quantify the characteristics of droughts in terms of its intensity, magnitude, duration and spatial extent. So far, subjectivity in defining drought has made it very difficult to establish a unique and universal drought index. Still, most studies related to the analysis of the phenomenon and its evolution are based on a) the Palmer Drought Severity Index (PDSI) based on an equation of subsurface water balance (Palmer, 1965), or b) Normalized Precipitation Index (NDVI), based on a probabilistic approach to precipitation (McKee et. al., 1993).
Drought can have a natural origin, that is to say, be explained by changes in atmospheric circulation patterns, variations in solar activity and the phenomena of interaction between the ocean and the atmosphere, such as El Niño. According to the FAO (Food and Agriculture Organization of the United Nations), drought is a global phenomenon that has been especially persistent during the period 2015-16 due to one of the most extreme Niño episodes in the last 50 years.
El Nino, a weather phenomenon that causes excessive heat and decreased rainfall in addition to food shortages, usually occurs at intervals of two to seven years and can last up to 18 months. El Niño has broad implications on weather and global climate regimes; in some regions it may lead to a decrease in rainfall and the occurrence of drought.
According to information from the Global Drought Monitor, on the European continent, drought conditions are concentrated at the higher latitudes, although lately have begun to extend any Central Europe.
In the past, droughts were not as catastrophic
In Asia, drought has persisted in the southeast, as well as in parts of India. In particular, in India, about a third of all the people have been afflicted by drought. Drought and heat continue to affect Thailand, Laos and Cambodia, leading to water and crops shortages and decimated herds.
