Water Resources

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Water Resources
Primary Source IPCC WG-2 Chapter 3
Freshwater Resources and Their Management
2
Human Activities Affecting Water Resources
less ET?
less precip?
clear land
drain?
irrigate?
(modified after Oki, 2005)
3
Human Activities Affecting Water Resources
more ET?
more precip ?
soil moisture?
veg. change?
(modified after Oki, 2005)
4
Drivers of Water Consumption?

• Population
• Food consumption
• Economic policy (including water pricing)
• Technology (increased efficiency, increased
  demand)
• Lifestyle (e.g., recreation)
• Societal value of freshwater ecosystems

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Human Vulnerability

• 25 of population in coastal regions
• lt 10 of renewable water supply
• rapid population growth
• Irrigation
• gt 70 of water withdrawals
• gt 90 of non-reusable, consumptive use
• Water-stressed basins have 1.5 - 2.1 billion
  people
• Increased efficiency can yield increased
  vulnerability!

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Current Water Stress
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Water-Stress Effects

• Amount
• Timing
• seasonality
• drought
• flood
• Quality
• - salinity
• nutrients
• temperature
• toxins
• pathogens
• sediments

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A simple surface water budget

• Precipitation Evaporation Runoff D Storage
• storage includes lots of things
• soil moisture, aquifers, reservoirs, withdrawals
  for irrigation, glaciers, snowpack, etc.

(From R. Arritt)
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Africa Geographic Changes
2080-2099 Minus 1980-1999 (A1B)
10
-1
50
-50
21
models with ? gt 0
0
10
Africa Water Balance Changes
models with ? gt 0
2080-2099 Minus 1980-1999
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South America Geographic Changes
2080-2099 Minus 1980-1999 (A1B)
10
-1
50
-50
21
models with ? gt 0
0
12
South America Water Balance Changes
10
-1
50
-50
21
models with ? gt 0
2080-2099 Minus 1980-1999
0
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Multi-Model Runoff Change
A1B Scenario
Agree on sign of change? white lt 66 stippled
gt 90
(derived from Milly et al. 2005)
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Runoff Change
SRES A2 2050s vs. 1961-1990
Seasonality?
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Groundwater Recharge
Using a global hydrological model - WGHM
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What is drought?

• One definition
• Elements of the definition
• deficiency of precipitation
• extended period (how long is "extended"?)
• water shortage for some user ("group or
  activity")

A deficiency of precipitation over an extended
period that causes water shortage for some group
or activity.
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Drought depends on the user

• Crops rely on stored soil water. Soil water can
  be rapidly depleted, so that monthly droughts may
  affect crops.

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Drought depends on the user

• Rivers and streams may dry out during seasonal
  droughts.

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Drought depends on the user

• Multi-year droughts may deplete ground water that
  supports communities.

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Drought, more precisely

• Must define the time period over which
  precipitation is below normal.
• Must define what is a water shortage that affects
  a particular activity.

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Iowa corn yields
1988 drought
1993 flood
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Recurrence of 100-yr Droughts

• IS92a emissions
• Business-as-usual water scenario

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Increased Water Stress
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Runoff Changes - Two Analyses
Agree on sign of change? white lt 66 stippled
gt 90
(derived from Milly et al. 2005)
A1B Scenario
(2081-2100) minus (1981-2000)
(derived from Nohara et al. 2006)
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Lake Mead
Riley christopher-gallagher
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Lake Mead Facts

• Lake Mead was formed in Black Canyon when the
  Hoover Dam was finished in 1935.
• Water source for over 22 million people.
• Lake Mead supplies water to
• Las Vegas
• 90 of the supply comes from Lake Mead
• Los Angeles
• San Diego
• Southern California Agriculture
• Extends 110 miles behind the dam
• Capacity is 28.5 million acre-feet
• Saylorville 641,000 acre-feet

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Lake Running Dry? The Causes

• Colorado River system is seeing a deficit of
• 1 million acre-feet of water per year
• This amount can supply 8 million people for 1
  year.
• The water supply is not being replenished
• 8 years of continued drought in the region
• Below average snowfall within the Colorado River
  watershed
• Human factors
• Human demand has increased as populations in the
  southwest have exploded.
• Increased evaporation off the lake
• Human induced climate change

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A Comparison

• Lake Mead has dropped over 100 feet in the last
  10 years to its lowest level since the 1960s.
• September 1998 June 2008

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Personal Experience (R. C.-G.)

• A photo I took of the The same view
  behind
• 1998 flood at the dam - the dam in June
  2008.
• water topped the 8 years of
  drought and over-use of water
• spillways for 4 days.
• May 1998 Las Vegas flood and above average
  snowfall

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Water Cycle Changes - Impacts
A1B Scenario
(2081-2100) minus (1981-2000)
(derived from Nohara et al. 2006)
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END
Water Resources