Effects of Climate Change on the Hydrologic Cycle

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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/klenzen
dorf.ppt
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Outline

• Introduction
• Colorado River Basin and Lake Mead
  Characteristics
• Climate Change Characteristics
• Summary and Conclusions

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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

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Source Barnett and Pierce, 2008
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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 gt Inflow)
• I(t) 15.1 MAF (or as low as 13.5 MAF)
• Q(t) 16.0 MAF (increasing trend)
• 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
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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

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No climate change
No climate change
Climate change included
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Climate Change Water Vapor

• Greenhouse gases (CO2, water vapor, etc) trap
  infrared radiation emitted from the Earths
  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
• Change in volume of evaporation equals volume of
  water vapor produced
• Constant Lv
• Water vapor is an ideal gas
• External pressure doesnt affect vapor pressure

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Climate Change Water Vapor

• CC Equation approximated as
• es in Pa
• T in oC

Atmosphere can hold more water
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Source Chow et al., 1988
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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
Source Held and Soden, 2006
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Climate Change Runoff
Average percent change in runoff volume compared
to historical conditions (1900-1970) from 12
climate models.
Source Milly et al., 2008
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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 Cant 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. 573-574.
• NASA (2003) EO Study Drought Lowers Lake Mead,
  Jesse Allen, National Aeronautics and Space
  Administration Earth Observatory, 21 February
  2008, lthttp//earthobservatory.nasa.gov/Study/Lake
  Mead/lake_mead.htmlgt
• 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, lthttp//www.usbr.gov/lc/region/g4000/
  hourly/mead-elv.htmlgt
• 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.
• See http//webspace.utexas.edu/jbklenz/ce394k/Klen
  zendorfFinalReport.htm for complete list of works
  cited.

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Questions?
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• This slide intentionally left blank.

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May, 2000
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Source NASA Earth Observatory
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May, 2003
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Source NASA Earth Observatory
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Source NASA Earth Observatory
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Average 18.0 MAF
Average 15.1 MAF
Average 13.5 MAF
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Source Woodhouse et al., 2006
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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

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Source Barnett and Pierce, 2008
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Drought 1125 ft
Lake Powell Constructed
Addition of new water intake at elevation 860 ft
by 2013 (ENR, 2008)
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Source USBR, 2008
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CRB Allocations

• 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

Source Barnett and Pierce, 2008
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• 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 Earths 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

Source Maidment CE 394K.2 class notes, 2008
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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 dont scale as the CC equation
  predicts
• Less change in precipitation and evaporation with
  increased temperature

a6.5
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Source Boer, 1993
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Runaway Greenhouse
Outgoing longwave radiation (OLR) is
representative of infrared radiation and can be
modeled as a function of temperature

• OLR of 260 W/m2
• Point a, T276 K, low RH, low CO2
• Point b, T288 K, high RH, low CO2
• Point c, T330 K, high RH, high CO2
• 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

Source Pierrehumbert, 2002
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Climate Change Runoff
Annual average of change in runoff compared to
the global modeling average.
Source Held and Soden, 2006
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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

Source Maidment CE 394K.2 class notes, 2008
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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

Source Maidment CE 394K.2 class notes, 2008