bushfire yield impacts with focus on 2003 ACT event Dr Robert Carr, - - PowerPoint PPT Presentation

Dr Robert Carr, Dr Geoff Adams, Dr Jin Wang eWater robert.carr@ewater.org.au

Hydrologic modelling of post- bushfire yield impacts with focus

• n 2003 ACT event

National Hydrological Modelling Strategy Agreements 2008+2018

• National Hydrological Modelling Strategy (NHMS), 2008 and Updated

2018 - Shared Integrated Platforms (Source+MUSIC)

• National Collaboration Framework (2018) – 15-year NHMS

Collaborative Head Agreement including IP Arrangements

• 5 year 1+2+2 Source Project Agreement. Completed FY19 now

contracted for FY20/21 for water sharing plan functionality.

• Several ongoing additional contracts for new functionality

Natural Resources, Mines and Energy

• https://ewater.org.au/casestudies/Bushfire-Hydrology/
• MIKE-SHE – (DHI, 2004) ACT Bushfire analysis and

projections - distributed model varying LAI and Root Depth a la Mountain Ash - high data requirements.

• Macaque (Watson et al, 1999) & (Feikema et al. 2011,

2013) – Detailed distributed model applied to mainly Melbourne Water’s catchments - high data requirements

• RAFIS (KS Tan et al, 2015) and Hydrofire (Wand et

al, 2016) assessment tools applied to Melbourne and Victorian Catchments.

Short list of Models Applied in Australia to Assess Bushfire Yield Response

Mountain Ash dies, Mixed Eucalypt have far lower mortality rates. Therefore each catchment should be assessed individually for forest type, soils, burn severity etc.

Ash and Mixed Eucalypt behave differently

Mixed species eucalypts Ash species Photos provided by Professor Patrick Lane Forest Hydrology The University of Melbourne

• Melbourne catchments dominated by debris flows, requires

unique risk assessment methods based on data.

• ACT catchments dominated by gully and sheet erosion (GHD,

2003)

• Adapted agricultural models (e.g. SEDNET, LASCAM,

IHACRES etc) appropriately parameterized for post-bushfire gully and sheet erosion likely representative of ACT load generation processes.

• ANU-led project on advanced WQ/Sediment algorithms for

Source is ongoing. CLOE (Catchment constituent LOad

Estimates) (Fu et al., in prep), a new plugin for Source to be

released

• Issue of model structure/complexity to represent the underling

hydrological processes

Water Quality & Sediment Modelling

Comparison of SWAT and Source (GR4J) Nguyen et al. 2019 SWAT 33 Parameters vs GR4J 4 Parameters GR4J model structure too simple to reflect land use changes Need to find the right balance

LASCAM – LArge Scale CAtchment Model for streamflow, salinity, sediments and nutrients

Developed by Viney and Sivapalan, 2000, adapted for eWater Source by Hall, 2011

• Developed initially for WA Catchments

to bridge the gap between fully distributed and lumped conceptual models.

• LASCAM ~28 parameters but could

be reduced to ~20 and further with a research project.

• Includes LAI and two-layer soil

representation for root depth

• Chosen for ACT because good for

representing land use changes including urban and forest.

ACT Upper Murrumbidgee Multi-Purpose Source Model

• LASCAM calibrated to 34

stream gauges 1980-2016

• 163 sub-catchments, 24 Land

Use Categories

• Water Quality constituents

modelled – T

• tal Suspended

Solids (TSS), T

• tal Phosphorus

(TP), T

• tal Nitrogen (TN and

Salinity.

Condor Creek at Threeways Cotter River at Gingera

Annual flows in the Cotter River at Gingera Annual flows in Condor Creek at Threeways

Climate shift in flows adds complexity

2003 Bushfires 2003 Bushfires

1994-2003 - catchments significantly drying

1) Despite climate shift, a well calibrated and appropriately structured model should provide a consistent rainfall/evaporation to runoff transformation through low and high rainfall periods. The hypothesis is that variations may be due to bushfire impact. 2) Calibrate the LASCAM model to the entire recorded sequence (1980-2016) 3) Compare the model performance across range of time scales covering pre-bushfire, early post-bushfire and late post-bushfire. 4) Test for statistical reliability of predictions

Is there a bushfire signal?

Period 1980 - 2016 1980- 2002 2003- 2007 2008-2016 Overall Pre- bushfire Early post- bushfire Late post- bushfire Mean Annual Rainfall (mm) 1,018 1,054 818 1,036 Observed % 18.5% 20.7% 12.3% 15.2% Modelled% 18.9% 20.4% 9.5% 19.3% Response Anomaly

• 0.4%

+0.4% +2.9%

• 4.0%

Analysis - Condor Creek at Threeways

Catchment is very disturbed with pine forests (formerly agriculture, compacted soils and significant post-bushfire remediation works) and areas of bare soil. So unlikely Mountain ash response. Statistically, the post-bushfire anomalies are 95% chance of being the same so most likely no significant response.

Period 1980 - 2016 1980-2002 2003- 2007 2008-2016 Overall Pre- bushfire Early post- bushfire Late post- bushfire Mean Annual Rainfall (mm) 1,177 1,242 982 1,127 Observed % 22.5% 22.9% 16.4% 23.8% Modelled% 21.7% 24.0% 12.4% 19.5% Response Anomaly +0.8%

• 1.1%

+4.1% +4.3%

Analysis – Cotter River at Gingera

• Increase in flows post-bushfire persists – response consistent with drier

unstructured soils, mixed Eucalypt with minimal disturbance.

• Post-Bushfire response is 95% chance of being higher than pre-bushfire

so likely slight increase in yield.

• Adoption of the Melbourne Ash catchment yield

reduction curves does not appear to be appropriate for ACT catchments.

• Mixed Eucalypt response is confirmed by the modelling

and can be scaled to assess other areas of the ACT.

Conclusions (1)

Fire response for mixed species eucalypt forests, (Nolan et al.2014, 2015) Note: Axis is ET, not yield

Graph provided by Professor Patrick Lane Forest Hydrology The University of Melbourne

• Two test catchments in bushfire-affected areas of

ACT’s Cotter catchment show yield responses between ‘no impact’ and ‘slight increase’ which is consistent with mixed Eucalypt.

• Appropriate Hydrological and Water Quality tools for

Bushfire response with moderate data requirements can be developed within the present Source platform for adoption though the NHMS for other Governments and Agencies to benefit.

• eWater Bushfire Hydrology community page will

reflect this information and ongoing updates.

Conclusions (2)

Thank You