Effect of climate change on water

From the UN Global Compact.

Broadly speaking climate change will cause:

• Increased variability in climate with more "severe weather events". Hence, increased heavy rainfall, more flooding and longer droughts.
• Loss of snow and ice.
• Higher temperatures in the atmosphere and sea.

This will affect water quality, supply and demand. This post summarises a few general statements made in the UN report to business and provides an overview of what might happen, but not much in the way of detail.

This rather cheery picture shows how supplies of freshwater may change by the end of the century (it's from the IPCC...)

These changes will probably cause:

Supply

1. Water shortages due to changes in rainfall and hence the water table. Drier in the subtropics and mid-latitudes which are already poor.

2. Glaciers and snowcaps reduced. One-sixth of population live in river basins fed by glaciers and snow melt. Notably China, India, Pakistan and western USA.

3. Damaged ecosystems due to temp increases, changes in rainfall and longer droughts. Ecosystems filter water and buffer against floods, but not when they deteriorate.

4. Flooding, extreme weather and sea-level rise will mess with existing water infrastructure (treatment and distribution). e.g. The future climate is likely to be more variable with floods followed by drought. Capacity to store large volumes during flood to carry through a drought may not exist. E.g. sea level rise could compromise water treatement.

5. Non-consumptive activities may be affected by drought, flood or extreme events. E.g.

Tourism that depends on snow or water;

Freight by river (e.g. Rhine in Europe, Mississippi in US);

Freshwater fisheries.

Quality

1. Extreme rainfall and floods increase erosion and contaminate water. Also wash soil based pollutants and toxins into fresh water.

2. Sea level rise can contaminate coastal surface and groundwater supplies (rivers, deltas and aquifers)

3. Increased algal and bacterial blooms due to higher temperatures.

4. Greater health risks e.g. flooding mobilises pathogens and contaminants.

Demand

1. Prolonged dry spells and drought increase irrigation demand. e.g. estimate is 40% increase in land needing irrigation by 2080.

2. Higher temps mean farm animals need more to drink.

3. More cooling water needed in industrial applications due to higher atmospheric and water temps.

Disasters

1. There's likely to be flooding and inundation of coastal areas, flood plains etc. due to sea level rise and heavier rainfall in certain places.

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!

SW WA water part 1 - surface water (rainfall)

Project to provide "robust estimates of current and future water yields for Western Australia’s south-west."

http://www.clw.csiro.au/publications/waterforahealthycountry/swsy/

Reported in 2010. Presentations and reports at the link above. There are three reports:
1. A summary that highlights possible shortfalls in 2030
2. A report on surface water supplies (rainfall and run-off from rain fall)
3. A report on ground water supplies (e.g. aquifers)

This post is a summary of the summary on surface water (rainfall)
It's going to rain less. The warmer it gets the less it rains. On average there will be 8% less rainfall and 25% less run-off. How bad it could get? Rainfall down 14% and runoff down 42% by 2030. Report does not go into what this will mean for agriculture, urban areas, policy etc.

Brief 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. 

Graphs of changes from SWSY-Summary-SurfaceWater.pdf

Main findings

It's going to get drier and the more the climate warms the drier it will be.

Rainfall declines in all three futures vs historical and recent. E.g. in "median" future "rainfall declines by an average of 8 percent and runoff by 25 percent relative to the historical climate.


In the future "streamflow" will decline by 800 gigalitres (GL) (for the median future) and by over 1400 GL under the dry extreme future climate. <How significant is that?>


Historically "the probability of rainfall exceeding 900 mm and runoff exceeding 130 mm in any one year is 20 percent. This probability reduces to 5 percent under the median future climate and to less than 3 percent in the dry"

Variability will increase substantially.

Days of low or no flow will increase.

Some numbers
Top section of table from the pdf. (Other rows, not copied, broke down results by geographical areas.) This table may be useful comparing for different scenarios and identifying just how bad it could get...rainfall down 14% and runoff down 42% by 2030.