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Effects of Climate Change 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

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Effects of Climate Change on the Hydrologic Cycle

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  1. 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

  2. Outline • Introduction • Colorado River Basin and Lake Mead Characteristics • Climate Change Characteristics • Summary and Conclusions 2

  3. 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 3

  4. 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

  5. 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) • Long term failure with negative net inflow 5

  6. 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 6

  7. 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 7 Source: Barnett and Pierce, 2008

  8. 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 8 No climate change No climate change Climate change included

  9. 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: • Change in volume of evaporation equals volume of water vapor produced • Constant Lv • Water vapor is an ideal gas • External pressure doesn’t affect vapor pressure

  10. Climate Change – Water Vapor • CC Equation approximated as: • es in Pa • T in oC Atmosphere can hold more water 10 Source: Chow et al., 1988

  11. 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

  12. Climate Change – Runoff Average percent change in runoff volume compared to historical conditions (1900-1970) from 12 climate models. Source: Milly et al., 2008

  13. 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 13

  14. 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!

  15. 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, <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. See http://webspace.utexas.edu/jbklenz/ce394k/KlenzendorfFinalReport.htm for complete list of works cited. 15

  16. Questions? 16

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  18. May, 2000 18 Source: NASA Earth Observatory

  19. May, 2003 19 Source: NASA Earth Observatory

  20. 20 Source: NASA Earth Observatory

  21. Average – 18.0 MAF Average – 15.1 MAF Average ~ 13.5 MAF 21 Source: Woodhouse et al., 2006

  22. 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

  23. Drought = 1125 ft Lake Powell Constructed Addition of new water intake at elevation 860 ft by 2013 (ENR, 2008) 23 Source: USBR, 2008

  24. 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

  25. CRB water balance model

  26. 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 26

  27. 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

  28. 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

  29. Climate Change – CC Relation • Model results don’t scale as the CC equation predicts • Less change in precipitation and evaporation with increased temperature α=6.5 29 Source: Boer, 1993

  30. 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, 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 • 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

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

  32. 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

  33. 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

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