A prolonged drought lasting two decades or longer.
1. The term megadrought is normally used to describe the drought's length, not its severity. In scientific literature the term is used to describe decades-long or multi-decadal droughts. Multi-year droughts, such as the Dust Bowl drought of the 1930s, are generally not described as megadroughts.
2. Past megadroughts have been associated with persistent multiyear La Niña conditions (i.e. cooler than normal water temperatures in the tropical eastern Pacific Ocean).