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.
To understand when droughts are occurring it's necessary to know how much water is around and how that compares to normal conditions.
Because people use water in so many different ways, there is no universal definition of drought. It's measured in different ways and at different timescales:
It is generally difficult to compare one drought to another, since each drought differs in the seasonality, location, geographic extent and duration of the associated rainfall deficiencies. Additionally, each drought is accompanied by varying temperatures, soil moisture and water availability. Monitoring the state of these elements and their impacts, and understanding how they compare to normal and historical conditions, helps us know more about the bigger drought picture.
An area experiences a rainfall deficit when the total rain received is less than the average rainfall for that period.