Trends in Australian rainfall: contribution of tropical cyclones and closed lows
- PDF / 1,841,852 Bytes
- 10 Pages / 595.276 x 790.866 pts Page_size
- 93 Downloads / 171 Views
Trends in Australian rainfall: contribution of tropical cyclones and closed lows Sally L. Lavender • Deborah J. Abbs
Received: 11 October 2011 / Accepted: 11 October 2012 / Published online: 27 October 2012 Ó Springer-Verlag Berlin Heidelberg 2012
Abstract Over the past 40 years there have been significant changes in Australian rainfall with increases in the north-west and decreases in the east. Tropical cyclones (TCs) and other closed low pressure systems are important synoptic systems that provide a large proportion of Australia’s annual rainfall. This study examines the proportion of rainfall that can be attributed to TCs over the 1970–2009 period, and to TCs combined with other closed lows over the 1989–2009 period. The contribution of these systems to Australian rainfall trends is also analysed. Tropical cyclones are found to have little influence on rainfall trends over the full time period. However, when the more recent 21-year period is considered, TCs and other closed low pressure systems can partially explain the positive rainfall trend in the north-west. Similarly, other closed low pressure systems, such as cut-off lows and east coast lows, can explain some of the negative rainfall trend in the southeast. The contribution of TCs and other closed low pressure systems to rainfall trends in the north and south-east is found to be predominantly due to respective increases and decreases in the rainfall producing efficiency of the systems. An understanding of the influence of these synoptic systems on Australian rainfall in the current climate is vital for evaluating how Australia’s water budget may change in future climates. Keywords Australian rainfall Tropical cyclones Rainfall trends
S. L. Lavender (&) D. J. Abbs Centre for Australian Weather and Climate Research, CSIRO, Marine and Atmospheric Research, PMB1, Aspendale, VIC 3195, Australia e-mail: [email protected]
1 Introduction Australian rainfall is highly variable on intra-seasonal to inter-annual timescales. Important drivers of Australian rainfall variability are known to include the El Nin˜oSouthern Oscillation, the Indian Ocean dipole and the Madden Julian oscillation (Risbey et al. 2009). These drivers are known to have varying influences on different regions of the continent, allowing for regional rainfall variability and trends. Changes in Australian rainfall over the last 40 years show a significant increase in rainfall over north-western Australia and a decrease in the east (e.g. Taschetto and England 2009; e.g. Smith 2004). The influence of ENSO on Australian rainfall is well-known with El-Nin˜o (La-Nin˜a) years resulting in dryer (wetter) conditions, particularly in the east of the continent. There has been an increase in the proportion of El-Nin˜o events in recent years which may explain some of the drying trend in the east, however the influence of ENSO is not as strong over north-west Australia and is unable to explain the positive rainfall trend over this region (Shi et al. 2008). The observed changes in rainfall have led t
Data Loading...
