ABSTRACT
Drought is a natural phenomenon characterised by a significant decrease of water availability during a significant period of time and over a large area (Nalbantis and Tsakiris, 2009 and Spiliotis et al., 2016). In other words, drought occurs when the water availability is below the canonical (e.g. mean) values. Drought must be considered a relative, rather than absolute condition. It occurs in both high and low rainfall (Wilhite et al., 2014). There are many types of droughts, while in this work we focus on the hydrological drought.
