PART II - RAINFALL

What do the maps show?

These maps show the average rainfall for various monthly and multi-month time spans, over the period 1981 to 2010. The time spans include annual, three-month seasons, both the northern and southern wet seasons, and the individual months. A monthly average is calculated using 30 years of monthly gridded rainfall data between 1981 and 2010. Seasonal and annual averages are calculated using the contributing monthly averages. For instance, when calculating a summer (December to February) climate average, a three-month average is formed from 1981-2010 average for December, January and February data separately, and then averaged again over the three-month period.

The annual rainfall map shows that extensive areas in central Australia are generally very dry. Rainfall in these areas is highly variable and falls on very few days. These areas are under the dominance of the subtropical high pressure belt for most of the year, and lie far from potential moisture sources. Rainfall, when it occurs, may result from north-west cloud bands.

Rainfall generally increases towards the coast as proximity to both moisture sources and reliable rain-producing weather systems improves. Elevation also has an important influence on rainfall, with the mountain areas of northeastern Queensland, southeastern Australia and western Tasmania receiving higher rainfall totals.

In the northern parts of the country, most of the rainfall is associated with active phases of the monsoon, occurring during the northern wet season (October to April). In southern Australia, most rain falls during the southern wet season (April to November) and is normally associated with frontal systems.

Source: http://www.bom.gov.au/jsp/ncc/climate_averages/rainfall/index.jsp?period=an&area=oz#maps