Transcript Effects of Global Warming on the Hydrologic Cycle

Effects of Climate Change on
the Hydrologic Cycle
The Future of Lake Mead
Presented by: Brandon Klenzendorf
CE 394K.2 – Surface Water Hydrology
Instructor: Dr. Maidment
April 29, 2008
https://webspace.utexas.edu/jbklenz/ce394k/klenzendorf.ppt
Outline
• Introduction
• Colorado River Basin and Lake Mead
Characteristics
• Climate Change Characteristics
• Summary and Conclusions
2
Introduction
• Project motivation:
– Barnett and Pierce (2008), “When Will Lake Mead Go
Dry?” article attributes global warming to low lake
levels. Is this true?!?
– Q: What do I know about climate change?
A: Not much!
• Problems to investigate:
– Current conditions of Colorado River Basin and
review of literature and causes of low lake levels
– Results of climate change on hydrologic cycle and
movement of atmospheric water
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Colorado River Basin (CRB)
• Total drainage area of
243,000 mi2
• Average annual
streamflow
– 15.1 MAF (1906-present
gage values)
– 13.5 MAF (tree ring
reconstruction values)
– 18.0 MAF (1920 allocation
value)
• Allocations governed by
“Law of the River”
– Allocations total 18 MAF, of
which over 16 MAF is
currently being utilized
4
Source: Barnett and Pierce, 2008
CRB Statistics
•
•
•
•
•
•
90% of streamflow generated in Upper Basin
70% of streamflow generated from snow pack
Average annual precipitation (P): 14.0 in.
Average annual evaporation (E): 12.2 in.
Average annual runoff (P-E): 1.8 in. (13%)
Allocations of 18.0 MAF:
–
–
–
–
7.5 MAF to Upper Basin
7.5 MAF (+1 MAF if necessary) to Lower Basin
1.5 MAF to Mexico
Additional minor water rights
• Negative net inflow (Outflow > Inflow)
– I(t) ~ 15.1 MAF (or as low as 13.5 MAF)
– Q(t) ~ 16.0 MAF (increasing trend)
dS
 I (t )  Q (t )
dt
• Long term failure with negative net inflow
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Literature on CRB Water Supply
• Global Change Research Act of 1990 called for
determining the effects of climate change on national
resources
• Multiple studies have found that human induced
increases in temperature of 2-4oC result in a runoff
reduction of 10-30% over the next 30-50 years
• More precipitation will fall as rain instead of snow + less
snow pack + earlier snow melt = change in timing of
peak flows
• Tarboton (1995) and others examined severe sustained
drought in CRB and found no major adverse impacts to
various drought conditions
• Use of general circulation models (GCMs) have shown
increases in temperature and evaporation, decreases in
precipitation and runoff; suggest failure of system
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Barnett and Pierce, 2008
• Provide first estimate of when Lakes Mead and
Powell will go dry
• 10% chance empty by 2013; 50% chance empty
by 2021
• Causes: global warming,
natural climate variability,
current operating status
• Used water balance model
and Monte Carlo simulations
to create CDF curves for
multiple scenarios
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Source: Barnett and Pierce, 2008
Barnett and Pierce, 2008
• Absence of climate change:
– Net inflow of -0.15 MAF in 2008
– Net inflow of -1.15 MAF by 2060
• CDF of system running dry based on net inflow
• Timing of wet/dry years still allows for failure with
zero net inflow
No climate change
No climate change
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Climate change included
Climate Change – Water Vapor
• Greenhouse gases (CO2, water vapor, etc) trap infrared radiation
emitted from the Earth’s surface
• Increased surface infrared radiation must be balanced by an
increase in sensible heat (temperature) and latent heat
(evaporation)
• Clausius-Clapeyron (CC) Equation:
–
–
–
–
es is saturated vapor pressure
T is temperature
Lv is latent heat of vaporization
Rv is water vapor gas constant
• Assumptions:
des
Lv es

2
dT RvT
– Change in volume of evaporation equals volume of water vapor
produced
– Constant Lv
s
– Water vapor is an ideal gas
– External pressure doesn’t affect vapor pressure
d (ln e )
  (T )
dT
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Climate Change – Water Vapor
• CC Equation approximated as:
 17.27T 
es  611 exp 

 237.3  T 
– es in Pa
– T in oC
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Vapor Pressure (kPa)
7
6
5
Atmosphere can
hold more water
4
3
2
1
0
-20
-10
0
10
20
30
40
Temperature (oC)
10
Source: Chow et al., 1988
Climate Change – Runoff
• Evaporation increases
across the Earth
• Precipitation decreases
for CRB
• Runoff (P-E) decreases
for CRB
• Current locations with low
runoff will get lower; high
runoff will get higher
• Areas of high runoff will
shrink with climate
change
• More extreme droughts
and floods
Evaporation
CRB
Runoff
CRB
Model predictions of change in runoff
for double CO2 concentrations.
Precipitation
11
Source: Held and Soden, 2006
Climate Change – Runoff
Average percent change in runoff volume compared to
historical conditions (1900-1970) from 12 climate models.
12
Source: Milly et al., 2008
Summary
• Colorado River Basin Summary
– CRB reservoir system will likely fail due to allocations
greater than streamflow
– Main problem is recent change to negative net inflow
due to increased water usage
– Climate change will only make the situation worse
• Climate Change Summary
– Increased temperature allows atmosphere to hold
more water vapor
– Increased evaporation in CRB
– Decreased runoff in CRB
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Conclusion
• Climate change will hurt the reliability of
reservoir system in the CRB. However,
the major problem is over allocation of the
river, and this problem is what should be
addressed.
• Take home message: Can’t blame global
warming for everything!
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Works
Cited
Barnett, T.P. and D.W. Pierce (2008): “When Will Lake Mead go Dry?”, Journal of Water Resources
Research, Vol. 44, W03201.
Boer, G.J. (1993): “Climate Change and the Regulation of the Surface Moisture and Energy Budgets”,
Climate Dynamics, Vol. 8, pg. 225-239.
Bosilovich, M.G., S.D. Schubert, and G.K. Walker (2005): “Global Changes of the Water Cycle
Intensity”, Journal of Climate, Vol. 18, pg. 1591-1608.
Chow, V.T., D.R. Maidment, and L.W. Mays (1988): Applied Hydrology, McGraw-Hill, Boston,
Massachusetts.
Held, I.M. and B.J. Soden (2000): “Water Vapor Feedback and Global Warming”, Annual Review of
Energy and the Environment, Vol. 25, pg. 441-475.
Held, I.M. and B.J. Soden (2006): “Robust Responses of the Hydrological Cycle to Global Warming”,
Journal of Climate, Vol. 19, pg. 5686-5699.
Milly, P.C.D., J. Betancourt, M. Falkenmark, R.M. Hirsch, Z.W. Kundzewicz, D.P. Lettenmaier, and
R.J. Stouffer (2008): “Stationarity is Dead: Whither Water Management?”, Science, Vol. 319, pg. 573574.
NASA (2003): EO Study: Drought Lowers Lake Mead, Jesse Allen, National Aeronautics and Space
Administration Earth Observatory, 21 February 2008,
<http://earthobservatory.nasa.gov/Study/LakeMead/lake_mead.html>
Pierrehumbert, R.T. (2002): “The Hydrologic Cycle in Deep-Time Climate Problems”, Nature, Vol. 419,
pg. 191-198.
Tarboton, D.G. (1995): “Hydrologic Scenarios for Severe Sustained Drought in the Southwestern
United States”, Water Resources Bulletin, Vol. 31, No. 5, pg. 803-813.
USBR (2008): Bureau of Reclamation: Lower Colorado Region, 5 March 2008, United States
Department of the Interior, Bureau of Reclamation,
<http://www.usbr.gov/lc/region/g4000/hourly/mead-elv.html>
Woodhouse, C.A., S.T. Gray, and D.M. Meko (2006): “Updated Streamflow Reconstructions for the
Upper Colorado River Basin”, Water Resources Research, Vol. 42, W05415.
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See http://webspace.utexas.edu/jbklenz/ce394k/KlenzendorfFinalReport.htm for complete list of works
cited.
Questions?
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May, 2000
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Source: NASA Earth Observatory
May, 2003
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Source: NASA Earth Observatory
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Source: NASA Earth Observatory
Colorado River at Lees Ferry - 10 Year Averages
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Gage Flows
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Tree Ring Flows
Streamflow (MAF)
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Average – 18.0 MAF
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16
Average – 15.1 MAF
15
14
Average ~ 13.5 MAF
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12
11
10
1500
1600
1700
1800
1900
2000
Year
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Source: Woodhouse et al., 2006
CRB Reservoir System
• Lake Mead
– Constructed in 1936 by Hoover Dam
– Provides water to 8 million people in California, Nevada,
Arizona, Mexico
– Total storage of nearly 30 MAF, over half for water supply
• Lakes Mead and Powell
– Combined storage of 52 MAF
– Account for 85% of total storage in CRB
22
Source: Barnett and Pierce, 2008
Lake Mead Elevation
1250
Spillway Elevation = 1221 ft
1200
1150
Elevation (ft)
1100
Drought = 1125 ft
Minimum Power Pool Elevation = 1050 ft
1050
Lower Water Authority Intake Elevation = 1000 ft
1000
Lake Powell
Constructed
950
900
1935
1945
1955
1965
1975
1985
1995
2005
Year
Addition of new water intake at
elevation 860 ft by 2013 (ENR, 2008)
23
Source: USBR, 2008
CRB Allocations
•
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•
•
Upper Basin at 5 MAF/yr and increasing
Lower Basin already at full allocation of 7.5 MAF/yr
Mexico already at full allocation of 1.5 MAF/yr
Additional loss to evaporation of about 1.5 MAF/yr
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Source: Barnett and Pierce, 2008
• CRB water balance
model
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Climate Change
• 1827 – Fourier said atmosphere will allow solar
radiation to enter uninhibited but traps thermal
radiation from the Earth’s surface
• 1861 – Tyndal said thermal radiation trapping is
not due to major gases (N2 and O2) but to trace
gases
• Major greenhouse gases
– CO2
– Water vapor, H2O
– Others (CH4, N2O)
• Mechanisms of climate change will not be
discussed here, only impact on hydrology
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Climate Change – CO2
• CO2 concentration from 1900-1920 is 300 ppm
• CO2 concentration at present day is 355 ppm
(Bosilovich et al, 2005)
• CO2 concentration to melt all permanent polar
ice is 1200 ppm (Pierrehumbert, 2002)
• Most climate models
investigate doubling of CO2
to roughly 700 ppm and find
an increase in temperature
of 2-4 oC
27
Source: Maidment CE 394K.2 class notes, 2008
Climate Change – Water Vapor
• The atmosphere can hold more water vapor at
higher temperatures
• This produces more clouds which warm the
surface in infrared (longwave, thermal) radiation
but cool the surface in shortwave (solar)
radiation (Boer, 1993)
• Therefore, increased water vapor in the
atmosphere will further act to increase surface
temperature and evaporation
• This will further increase atmospheric water
vapor concentrations
• Result: possible “runaway greenhouse” effect
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Climate Change – CC Relation
• Model results don’t
scale as the CC
equation predicts
• Less change in
precipitation and
evaporation with
increased
temperature
29
Source: Boer, 1993
Runaway Greenhouse
• OLR of 260 W/m2
– Point a, T=276 K, low RH,
low CO2
– Point b, T=288 K, high RH,
low CO2
– Point c, T=330 K, high RH,
high CO2
Outgoing longwave radiation (OLR) is
representative of infrared radiation and can
be modeled as a function of temperature
• OLR of 300 W/m2
– Point a’, T increases by 14 K
– Point b’, T increases by 30 K
– Water vapor feedback
• Kombayashi-Ingersoll limit
– How fast can a moist
atmosphere loose energy by
infrared radiation
30
Source: Pierrehumbert, 2002
Climate Change – Runoff
Annual average of change in runoff compared
to the global modeling average.
31
Source: Held and Soden, 2006
Climate Change – Runoff
• Current precipitation
trends controlled by
wind circulation
• These trends intensify
due to climate
change, so dry areas
become drier and wet
areas become wetter
32
Source: Maidment CE 394K.2 class notes, 2008
General Circulations Models (GCMs)
• Focus only on
troposphere
• Horizontal resolution of 2o
to 4o latitude and
longitude
• Vertical resolution of 10
to 20 layers
• Assume constant relative
humidity
• Assume constant lapse
rate
• Unable to resolve small
scale phenomenon
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Source: Maidment CE 394K.2 class notes, 2008