SW WA water supplies in 2030

The future of water in SW WA...

Overview (from CSIRO report)
It's going to get hotter and drier (big surprise there!).

Rainfall will decrease by up to 18%, resulting in around 25 to 50% less run-off into stream and rivers.

Groundwater (in aquifers) won't be affected much by climate change.

The region currently takes about 75% of its water from ground water.

If the climate doesn't get too hot and demand doesn't grow too quickly, then there will enough water in 2030.

If either the climate gets hot, or demand grows rapidly, then there won't be enough water in 2030.

Either way, there will be localised issues. The two statements above ignore water quality and transportation. Taking these two factors into account means there are likely to be water deficits in horticulture (Harvey), coal mining (Collie) and urban supply (Perth). 

"Under current per-capita water consumption levels, rapid population and economic growth, along with the reductions in water yields, are expected to result in appreciable water deficits developing near Perth and some regional cities in south-western Australia by 2030." (Source)

As a result... 

"Seawater desalination is expected to become the main drinking water supply in the next few years" (source)

In the worst case scenario (high demand and a hot climate), the shortfall in available water across the region would be about 250 Giga Litres (GL) per year. Perth metropolitan area currently consumes about 250 GL/year...ouch...looks like a limit to growth...or an incentive to consume less*

*One estimate is that current per capita use needs to fall by about 10%, from 149 KL/year to 134 KL/year

Brief description of methodology
Forecast out to 2030, using three possible future climates: "wet extreme, median and dry extreme future climate". These were compared to "historical" (1975 - 2007) and "recent" (1997 - 2007) climate models. They also considered a "future development" model, that assumes growth in demand.

Where water comes from

There appear to be two sources of water: groundwater (aquifers) and surface water (rainfall and it's subsequent run-off). This map shows how they are distributed.


Where the rainfalls
It rains the most in the SW (about 1200mm/year) and least in the NE (less than 350mm/year) of the area. (These are, of course, averages!)

There's a lot of water loss to evaporation in the NE (about 1650mm/year) and less in the SW (about 1180mm/year).

So overall there is a deficit of rainfall in the NE (350 - 1650 = -1300 mm/year) and a bit to spare in the SW (1200 - 1180 = 20 mm/year). That's the averages. Extremes appear to be a deficit of about 1350 mm/year in the NE and a surplus of 150mm/year in the wettest bits of the SW).


It's going to rain less

It's going to rain less

As the climate warms up, it will rain less. Depending on the climate model used and the forecast of how much the climate will change, the predicted fall in rainfall by 2030 varies from about 1% less to about 18% less. The diagram shows the data.

The reports translates this to "water yields" from rainfall, which seems to be the water available from streams and rivers. These will decline by an average of 24% in the "median" scenario; and range from 4% to 49% lower. Presumably 49% comes from the "hot" scenario.

And this also translates into less flow in rivers which could affect ecosystems dependent on high flows.

And, regions that depend on surface water will be in deficit by 2020, assuming continued increase in demand. In English this means that areas like Harvey (horticultural irrigation) and Collie (coal mining) won't have enough water to meet demand. Bad news for those who like to eat, good news for those who would like to see fewer fossil fuels in use?

Groundwater seems OK
Groundwater supplies are more resilient to climate change. Yields are likely to be between only 2% lower by 2030 and may actually have increased. However, certain ecosystems (such as wetlands) are sensitive to changes in groundwater levels and may be affected by climate change.

About three-quarters of the regions water demands come from groundwater (as opposed to rainwater).

Demand for ground water is forecast to increase by between 10 and 57% by 2030. The median is about 35%. The range depends on predictions for population and industrial growth. This will result in deficits in groundwater availability in the Perth, Collie and Albany regions.

What it all means
Putting together groundwater and surface water supply and the projected demand for the various "future climate" scenarios, suggests the region has enough water in most cases. The main problem arises if there is high growth in demand linked to full belt climate change. The diagram below summarises the data. 

However, these numbers ignore water quality and transportation issues...so in actual fact, this isn't as good as it first seems! So, for example, Perth is expected to have significant gaps between yield and demand for groundwater by 2030. At it's worst, the deficit could be 250 Giga Litres (GL)/year. To put that in context, Perth currently uses about 700 mega litres (ML) of water a day (http://www.watercorporation.com.au/s/supply.cfm). So, a deficit of 250 GL/year over the whole region would mean Perth city would have no water for 357 days each year...ouch!