Climate and landuse change impacts on water availability: a case - - PowerPoint PPT Presentation

Climate and landuse change impacts on water availability: a case study from Tasmania, Australia

David Post HydroPredict 2010 Prague, 20-23 Sep 2010

Background

• Australia is the driest inhabited continent. In order to effectively

manage its water resources, detailed, accurate (and therefore reliable) assessments of water availability are required.

• The Australian Government has commissioned CSIRO to carry out

water availability assessments for some of the major river systems across the country.

• This presentation gives the methods used and some results for one

such ‘sustainable yields’ project – for Tasmania, an island state in south eastern Australia where there are State and Commonwealth plans to increase the area of land under irrigated agriculture.

Northern Australia 1.25m km2 $5.7m July 2009 Western Australia 0.08m km2 $5.2m February 2010 Tasmania 0.05m km2 $4.2m February 2010 Murray-Darling 1.01m km2 $11m October 2008

‘Sustainable yields’ project areas

Overview of project methods

Climate and scenario definition

• Rainfall-runoff and

recharge modelling Groundwater modelling and assessment River system modelling and assessment Run off

Rech arge

Reporting Ecological assessment

• Historical climate
• Future climate
• Future development

Historical climate

Future climate

• Calculate change in seasonal rainfall per degree global warming for

15 of the 23 GCMs in IPCC AR4

• Scale daily rainfall amounts differently depending on their size

100 200 300 400 500 600 700 800 900 12.0 12.5 13.0 13.5 14.0 14.5 15.0 15.5 Annual global temperature (°C) Summer rainfall (mm) .

5 10 15 20 25 30 10 20 30 40 50

Percent time daily rainfall is exceeded Daily rainfall (mm)

1981–2000 2046–2065

Dynamic downscaling

• Use spatial patterns of

projected changes from dynamically-downscaled CCAM model to scale GCM results.

Rainfall-runoff modelling

• Calibrate 5 models

(SIMHYD, Sacramento, IHACRES, SMARG, AWBM) to 90 unregulated catchments

• Evaluate model

performance through cross-validation using parameters from the nearest neighbour

• Choose optimal model and

regionalise to ungauged areas.

Changes in rainfall and runoff by ~2030

+1%

• 2%
• 6%
• 8%
• 3%

+2% Rainfall Runoff

Reporting metrics

5000 10000 15000 20000 25000 Dry extreme future climate Median future climate Wet extreme future climate Historical climate Average annual volume (GL) . Non-extracted water Extracted water

50 100 150 J F M A M J J A S O N D Mean monthly runoff (mm) x Future range Future median Historical 0.0 0.1 0.1 0.2 0.2 0.3 0.3 0.4 0.4 0.5 J F M A M J J A S O N D Month EOS monthly flow (GL) .

Future range Future median Historical Without extractions

• 25
• 20
• 15
• 10
• 5

J F M A M J J A S O N D Month Percent change in EOS monthly flow due to development . Range Median 1 10 100 1000 10000 100000 20 40 60 80 100 Percent time volume is exceeded EOS daily flow (ML) .

Reporting metrics

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0% 20% 40% 60% 80% 100% Percent of years exceeded Extracted volume per . unit allocated . Future range Future median Historical

0.0 0.2 0.4 0.6 0.8 1.0 0% 20% 40% 60% 80% 100% Percent of years exceeded Extracted volume per . unit allocated . D range Dmid 1 2 3 4 5 0% 20% 40% 60% 80% 100% Percent of years exceeded Annual volume (GL) . Future range Future median Historical

Annual allocation (GL)

1 2 3 4 5 6 0% 20% 40% 60% 80% 100% Percent of years exceeded Annual volume (GL) . D range Dmid

Annual water demand (GL)

Ecological impacts

Historical climate Dry extreme future climate

• 2% of subcatchments

and 15 key ecological sites are potentially impacted:

• 10 river sections
• 4 riverine wetlands
• 1 Ramsar wetlands
• 0 estuaries
• 1% of subcatchments

and 13 key ecological sites are potentially impacted:

• 8 river sections
• 1 riverine wetlands
• 2 Ramsar wetlands
• 2 estuaries

Conclusions

• A method has been developed which allows estimates of current and

future water availability to be made across very large regions.

• The method includes assessments of changes in water availability due to

changes in climate, as well as impacts due to catchment development such as forestry, irrigation and groundwater extractions.

• The method produces a wide range of reporting metrics, including:
• Spatial patterns of changes in rainfall and runoff
• Current and future water availability and use at catchment scale
• Reliability of proposed future irrigation development schemes
• Impacts of climate change and catchment development on streamflows
• Ecological impacts of projected changes in streamflows.