Drought is a prolonged, abnormally dry period when the amount of available water is insufficient to meet our normal use. Drought is not simply low rainfall; if it was, much of inland Australia would be in almost perpetual drought.
Because people use water in many different ways, there is no universal definition of drought. Meteorologists monitor the extent and severity of drought in terms of rainfall deficiencies. Agriculturalists rate the impact on primary industries and their dams and water tanks, hydrologists compare ground water levels, and sociologists define it by social expectations and perceptions.
http://www.bom.gov.au/climate/drought/#tabs=What-is-drought
https://www.abc.net.au/news/2020-01-27/how-long-until-drought-stricken-towns-run-out-of-water/11655124?pfmredir=sm
https://www.farmonline.com.au/story/6314940/heres-how-the-worst-drought-on-record-looks-from-space/