Global Change Effects on Water Supplies

• Global inventory:

- Oceans 98.897 %

- Ice 1.060 %

- Underground 0.035 %

- Lakes and rivers 0.007 %

- Atmosphere 0.001 %

The Hydrologic Cycle

The Hydrologic Cycle

• Groundwater and runoff (stored in reservoirs) are the main, and practically speaking, only sources of water usable for drinking, agriculture, etc.

Supply and Demand

• Precipitation does not always (rarely!) fall where the demand is.

Who Uses What?

Groundwater

Aquifers

What Happens When One Pumps From An Aquifer?

Groundwater Contamination as a Result of Pumping

Existing Saltwater Intrusion Problems Due to Pumping Alone

• Approximate 4.2 million people depend on the Biscayne aquifer for water.

Existing Saltwater Intrusion Problems Due to Pumping Alone

Saltwater Intrusion as a Result of Sea Level Rise

• Increase in sea level forces saltwater further into the aquifer.

Additional Effects of Groundwater Pumping

• Freshwater demand is likely to increase due to a growing population and changes in precipitation/recharge patterns.

- Subsidence!

Groundwater-Related Subsidence

• Water helps support the surrounding and overlying ground.

Groundwater-Related Subsidence

• In areas where the underlying geology is predominantly limestone (calcium carbonate), groundwater will dissolve some of the rock over time.

H2O + CO2 + CaCO3 Ca2+ + 2HCO3-

Tangent – Caves!

Groundwater-Related Subsidence

Groundwater-Related Subsidence

Other Groundwater Issues – Ogallala Aquifer

• Primarily used for agriculture.

• Water was stored coming out of the last ice age. Modern recharge is negligible.

• Development led to a 100-foot drop in the water table by the mid-1980’s.

• Will likely empty it within decades.

Surface Water

• Surface water exists where the land surface meets the water table.

Surface Water

• Several big issues here:

- potential changes in where the precipitation falls.

- type of precipitation (snow versus rain).

- loss of natural reservoirs.

Surface Water

• Relative changes in precipitation for the period 2090-2099 relative to 1980-1989. White areas are where less than 66% of the models agree. Stippled areas are where more than 90% of the models agree.

Surface Water• Aqueducts

Surface Water

Surface Water

Surface Water – Colorado River Compact

• In 1922 seven western states came up with an agreement to share the water from the Colorado River and its tributaries.

• Rapid development led to heavy water use leading to decreasing volume and water quality.

• By the mid-1960’s the lower part of the river had a total dissolved solid content of 2700 ppm (2.7 g/kg, about a tenth of that of seawater).

• U.S. built Mexico a desalinization plant as a result of a lawsuit.

Surface Water – Colorado River Compact

• River survey done during an unusually wet period …

• Water divided up by volume rather then percent!

• Low reservoir levels in many places around the world!

Surface Water – Aral Sea

Surface Water – Aral Sea

• Diversion of water draining into the Aral for irrigation has caused the lake to shrink.

- in 14 years, the Aral went from being the 4th to the 6th largest lake in the world

Surface Water – Aral Sea

• Remaining water has a salinity nearly twice that of the ocean.• Blown salt from the dried lakebed harming agriculture and causing respiratory problems.

Surface Water – Rain and Snow

• Snow and ice are critical parts of the hydrologic cycle in mountainous regions and at high latitudes.

• Water stored in the frozen state is released during Spring, providing water for the rest of the year.

Surface Water – Rain Versus Snow

• Two issues here:

1) If the precipitation falls as rain it may overflow reservoir capacities, and that water must then be released.

Surface Water – Decreasing Snow and Melting Snowpack

• Two issues here:

2) Mountain glaciers act as frozen reservoirs, and 80-90% of mountain glaciers worldwide are

receding.

1948 2002 2006

Switzerland

Washington

Surface Water – Decreasing Snow and Melting Snowpack

Himalayas

Surface Water – Decreasing Snow and Melting Snowpack

Surface Water – Decreasing Snow and Melting Snowpack

Bolivia

Surface Water – Decreasing Snow and Melting Snowpack

Mt. Kilimanjaro, Africa

• More than 2 million people depend on Mt. Kilimanjaro’s ice and snow for water.

• Projected to be gone within the next twenty years.

Where to go for Water?

• Need to make undrinkable water drinkable.

- Filtration

- Distillation

- Reverse osmosis

Where to go for Water?

Now What?

• More so than temperature increases or sea level rise, diminishing or changing water supplies will likely be the a critical test of our ability to adjust to a changing climate.

- Change the way we use water (conservation, water reclamation).

- Infrastructure to move water from where we have enough to where we don’t.