Tropical Cyclone Contribution to Rainfall over Australia

Tropical cyclone (TC) rainfall over the Australian continent is studied using observations from 41 TC seasons 1969/70 to 2009/10. A total of 318 storms, whose centers either crossed the coastline or were located within 500 km of the coast, are considered in this study. Mean seasonal (November/April) contributions by TCs to the total rainfall are largest along the northern coastline from 120 degrees-150 degrees E. However, the percentage contributions by TCs are greatest west of 125 E, with mean coastal values of 20%-40% and inland values of approximately 20%. Farther east, percentages near the coast are only around 10%, and even lower inland. Inland penetration by TC rainfall is generally greatest over western portions of the continent, associated with greater inland penetration of TC tracks. During the peak of the TC season (January March), TCs contribute around 40% to the rainfall total of coastal regions west of 120 degrees E, while during December. TCs contribute approximately 60%-70% to the total rainfall west of 115 degrees E. Rain from TCs varies sharply between TC seasons, with some longitude bands receiving no TC rain during some seasons. For the 110 degrees-115 degrees E longitude band the TC rain contribution is quite inconsistent, varying interannually from 0%-86%. This has an impact on water supplies, with storage dams falling to low levels during some years, while filling to capacity during TC-related flood events in other years. These large interannual variations and their impacts underline why it is important to understand TC rainfall characteristics over the Australian continent.