Drought is widely regarded as a complex, multifaceted meteorological and hydrological phenomenon. Unlike other natural hazards, drought develops slowly and it can be difficult to determine the onset, development and decay of an event. Drought can occur in any climate and has widespread impacts on both the environment and society (Shukla & Wood 2008). Wilhite & Glantz (1985) identified four categories of drought: meteorological, hydrological, agricultural and environmental, although others such as socioeconomic and groundwater droughts have also been described (Mishra & Singh 2010). Depending on a drought’s cause and duration, various human activities and natural processes, it may propagate through these categories, affecting different parts of the hydrological cycle and water resource system. These factors make it difficult to give drought a single definition (Lloyd-Hughes 2013), which in turn, can impede effective monitoring, forecasting and management of droughts. However, the Monitoring and Early Warning (M&EW) of droughts is crucial for the reduction in scale and magnitude of drought impacts, for example on water supply, agriculture and ecology.