Project SW1: Baselines, drivers and trends for forest water catchments

The Forest Monitoring Steering Committee commissioned the University of Melbourne to deliver baselines, drivers and trends for water quality and quantity in the NSW Regional Forest Agreement (RFA) areas.

Following this work, the University of Melbourne was asked to extend this analysis to other forested catchments in NSW. In doing so, the researchers applied novel statistical approaches to identify the flow responses to climate variability to identify any impacts from catchment disturbance, specifically fire.

The researchers have now delivered final reports for the baselines analysis in the RFA regions and the extended state-wide analysis.

The findings

The full findings and analysis are available in the final report for RFA regions and extension final report for state-wide analysis.

In summary:

  • Annual flows have decreased in forested catchments over the last 35 years, with most significant decreases in the RFA region in south coast forests.
  • One third of coastal forest catchments had 10% to 20% flow decrease relative to the long-term average, with similar findings for almost half of the catchments outside of the RFA areas.
  • In RFA regions, flow reductions were generally smaller for catchments with a higher mean annual flow, greater area of national park, greater accumulated area harvested, or greater accumulated area burnt.
  • Outside of the RFA regions, catchments with higher mean annual flow and catchments with a greater percentage of area used for grazing experienced greater percentage decline in flow.
  • At the catchment scale, historical changes in flow are generally more heavily affected by hydro-climatic drivers than fire events, although some impacts on streamflow due to fire events were observed.
  • There were mixed and inconclusive results across water quality indicators.

The approach

The researchers:

  • Identified key indicators of water quantity and quality in across all tenures.
  • Established a conceptual framework for analysing baselines/trends and opportunities for future monitoring of proposed key indicators across all tenures.
  • Developed historic baselines for the indicators of water quality and quantity across all tenures.
  • Proposed additional baselines for the indicators for which there is no current data.
  • Analysed trends in the indicators of water quality and quantity across all tenures.
  • Applied statistical analysis to identify potential drivers for water quality and quantity trends including climate and catchment disturbance (fire).

Papers and reports

Soil and water resources - forest water catchments:

Published papers

Researchers funded under the NSW Forest Monitoring and Improvement Program have published an article How does wildfire and climate variability affect streamflow in forested catchments? A regional study in eastern Australia in the peer-reviewed Journal of Hydrology.

The researchers compared the influence of wildfire and climate forested catchment stream flows over multiple years. They found wildfire showed less impact on streamflow than climate over longer time periods. The results highlight the role of climate on water resources in forested catchments and the need to consider changing climatic conditions at the catchment scale.

Access the paper at Science Direct - Journal of Hydrology

Full citation: Danlu Guo, Margarita Saft, Xue Hou, J. Angus Webb, Peter B. Hairsine, Andrew W. Western, How does wildfire and climate variability affect streamflow in forested catchments? A regional study in eastern Australia, Journal of Hydrology, Volume 625, Part A, 2023, 129979, ISSN 0022-1694.

Data

The report, methods and project data for RFA regions can be found on the NSW SEED. Data also can be visualised and interacted with through the Spatial Collaboration Portal.

The project data for NSW will soon be uploaded to NSW SEED portal.