Rainfall & its variability

Indicator description

Of all the standard climatic parameters, rainfall is the most variable in time and space. The amount of rainfall received across the Australian Capital Region can vary dramatically from year to year, ranging from dry periods that can persist for years, to periods of intense downpours, storms and flooding. On average, the region falls into the zone of uniform seasonal distribution of rainfall (i.e. it has no clearly defined wet or dry season), but this too can vary greatly between years.

Together with temperature, the features of rainfall variability in time and space across the region affect the distribution of the flora and fauna. Many species have adapted to cope with the wide range of variability that has characterised Australian rainfall for millennia. Rainfall is also a key determinant of the growing season and the types of agriculture practised - as water is limiting for many human activities. It directly influences surface runoff, streamflow and groundwater recharge.

There are several measures of rainfall that can be used to provide information on variability and hence on the state of the climate. These include:

• annual rainfall totals
• rainfall seasonality
• the frequency of extreme events.

Data for each of these are considered for the current reporting period, and for the longest period for which data are available; wherever possible they are compared with long-term mean values.