Latest research - tracing the origins of moisture for precipitation

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Mean moisture contribution to Australian precipitation in each season, with mean climatological low-level wind vectors.

Mean moisture contribution to Australian precipitation in each season, with mean climatological low-level wind vectors.

A team of Australian climate researchers recently investigated the origin of moisture for regional precipitation and the relative importance of local versus remote processes. Where does our moisture leading to rain come from?

Knowing the long-term average regional source of moisture provides insight into the drivers of precipitation during anomalously dry or wet periods. In the case of drought, for example, identifying the long-term average source regions can help reveal whether the low precipitation was due to a reduction in source evaporation, anomalous atmospheric circulation or a lack of local precipitation generating mechanisms.

Key findings of the study;

  • In summer, moisture for the Australian continent generally was primarily sourced from Australia’s Maritime Continent (waters around Philippines/Indonesia/Papua New Guinea)

  • Summer precipitation in the Murray Darling Basin (MBD) was primarily sourced from the Tasman Sea, Southern Ocean and land within the basin itself.

  • The MBD recycled more moisture from land sources for precipitation than any other eastern basin, with a maximum of 9.2% across the year.

  • The Australian continent receives a minimum of 77% of moisture from marine sources in summer and a maximum of 89% in winter, with the remainder recycled from land sources.

  • North-West Cloud Bands relating to the Indian Ocean Dipole interact with moisture from condensed moist air from the Tasman Sea to deliver precipitation to the MDB during spring.

What does all of this mean?

Coming into summer season, the distribution of warm waters around our perimeter does impact rainfall, although atmospheric processes involved to deliver that moisture is a whole other story!

We hope the land-sea interaction is captured in General Circulation Models, although it’s worthy of periodical monitoring the Sea Surface Temperatures in those areas identified by researchers and compare with other similar years.

Paper: Holgate, C.M., Evans, J.P., Van Dijk, A.I.J.M., Pitman, A.J. and Di Virgilio G. Australian Precipitation Recycling and Evaporative Source Regions (2020) Journal of Climate. https://doi.org/10.1175/JCLI-D-19-0926.s1