TRaCK: Tropical Rivers and Coastal Knowledge

Science and knowledge that governments, communities, industries for sustainable use of Australia's tropical rivers and estuaries

Precipitation partitioning for three land cover classes in the wet-dry tropics of Australia

TitlePrecipitation partitioning for three land cover classes in the wet-dry tropics of Australia
Publication TypeConference Participation
Year of Publication2009
AuthorsWeinmann, RA, Hutley, LB, Petheram, C
KeywordsEvapotranspiration, Human impacts, Hydrology, Land/atmosphere interactions, Soil moisture, Water budgets

The savannas of the northern Australian tropics cover approximately a quarter of the Australian continent. These wet-dry tropical systems are driven by the north Australian monsoon, which has created an extreme environment, with the region's highest rainfall occurring during a 3-4 month wet season, followed by a sustained dry season that lasts the majority of the year. There is little knowledge about the runoff characteristics of most of the catchments in this region, and the impact that wide spread clearing of these savanna systems will have on the water balance is hard to predict. With the increasing pressure to develop the Daly River region in the Northern Territory, an ongoing Tropical Rivers and Coastal Knowledge (TRaCK) project was set up to look at the impact that clearing savanna woodland will have on the water balance of the Daly River catchment. Some of the results from this study are presented in this paper. Three sites within a sub-catchment of the Daly River system have been instrumented to monitor rainfall, evapotranspiration, soil moisture dynamics and deep drainage. The selected sites represent the major land use classes in the Daly River area. These sites are an uncleared woodland savanna, an improved pasture site cleared 25 years ago, and an unmanaged regrowth site that was a native grass pasture cleared 8 years ago. Using data from the past two wet seasons, we have partitioned the precipitation into its evapotranspiration and infiltration components and will show how clearing modifies these water balance components across 3 contrasting land cover types. Preliminary results show that the modified pasture site has the most seasonal evapotranspiration, and that the uncleared woodland savanna is stabilised by the influence of the evergreen eucalypt trees, resulting in the least variable evapotranspiration. We also see that the deep rooting trees in the uncleared savanna site significantly draw on soil water throughout the long dry season, resulting in lower soil moisture and decreased drainage to surface aquifers at this site. Further results will confirm that clearing of the native savanna in the Daly River area will result in an increase in the runoff of the catchment.