Drought in general means acute water shortage.
The Bureau's drought maps
highlight areas considered to be suffering
from a serious or severe rainfall deficiency.
These classes are assigned by first examining rainfall
periods of three months or more for selected places
throughout Australia to see whether they lie
below the 10th percentile (lowest 10% of records).
The terms serious and
severe are defined by -
- Serious rainfall deficiency:
rainfall lies above the lowest five per cent of
recorded rainfall but below the lowest ten per
cent (decile range 1) for the period in question,
- Severe rainfall deficiency:
rainfall is among the lowest five per cent for
the period in question.
Areas where the rainfall is lowest on record for the
given time period are also shown.
Drought declaration is the responsibility of
State and Federal Governments which must consider other
factors apart from rainfall,
however the Bureau of Meteorology's Drought Statement
assists by providing rainfall information to all interested parties.
Defining the end of a rainfall deficiency period of less than 12 months
Defining the end of a period of rainfall deficiency is a difficult matter,
and presents more problems than defining the start. However, the
following definitions which were used in the days of hand-drawn analyses,
still provide useful guidance as to whether there has been significant
relief from a period of rainfall deficit. They are only applicable to
periods of about 12 months or less, and great care in their
interpretation is needed in those areas which have a distinct wet and
dry season in the annual rainfall cycle. The criteria are:
- The rainfall of the past month already exceeds
the 30th percentile for the three-month period commencing that month, or
- Rainfall for the past three months is above the 70th percentile for