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Where Will the Water Go? Hydrologic Impacts of Climate Change

Where Will the Water Go? Hydrologic Impacts of Climate Change. David Purkey, SEI and Richard M. Vogel Department of Civil and Environmental Engineering Tufts University SEI Climate Change Symposium Tufts University November 30, 2007. Background and Motivation I.

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Where Will the Water Go? Hydrologic Impacts of Climate Change

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  1. Where Will the Water Go?Hydrologic Impacts of Climate Change David Purkey, SEI and Richard M. Vogel Department of Civil and Environmental Engineering Tufts University SEI Climate Change Symposium Tufts University November 30, 2007

  2. Background and Motivation I • Previous national water resource assessments were completed 30-40 years ago: • Wollman and Bonem, 1971; Water Resources Council 1968, 1978 • National Water Commission, 1973 • Methods introduced here apply to local, regional, national and global Climate and Water Assessments • Water Availability Is Impacted by Climate, Land Use and Water Use and their Interactions and Changes

  3. Background and Motivation II Many recent innovations enable us to perform water resource assessments at extremely fine spatial and temporal scales. Intellectual quest for an analog to the ‘Mach number’ or ‘Reynolds number’ for hydroclimatic systems

  4. Background and Motivation IIIBalancing Water for Humans and NaturebyMalin FalkenmarkandJohan Rockström2004

  5. Methodology for a National/Global Water Census Many of the following ideas arise from a collaboration with Peter Weiskel (USGS) and others resulting in: Weiskel, P.K., R.M. Vogel, P.A. Steeves, P.J. Zarriello, L.A. DeSimone and K.G. Ries, III, Water-Use regimes: Characterizing direct human interaction with hydrologic systems, Water Resources Research, 43, W04402, 2007 and several other papers in progress.

  6. Traditionally, water availability is defined in terms of NET water balance of a watershedP – ET = SWout* water availability = runoff * reflects both the traditional water-supply perspective,and an aquatic-focused ecological perspective P P = Precipitation; ET = Evapotranspiration SWout = Surface-water runoff Assume that GWin = GWout = 0

  7. Consider total instead of net water balance…P = SWout + ET * considers both: “green water” (ET) demands of terrestrial ecosystems, including rainfed agriculture, and “blue water” (SWout) demands of aquatic ecosystems and human withdrawals. See Falkenmark and Rockström, 2004

  8. From watersheds to hydrologic units … SWin + P = SWout + ET * Considers landscape position, as well as climate. * considers both green and blue water Recent GIS datasets (or gridded models) are essential to this approach: (i.e. National Hydrography Dataset, PRISM Climate Data, etc.) Unit 1 Unit 2

  9. Hydroclimatic Regimes4 Extreme End-members Arise From Total Water Balance P P ET SW + GW headwater no-flow headwater source ET SW + GW SW + GW terminal flow-through terminal sink (from Weiskel, Vogel and others., in prep.)

  10. Example fromNew England Potential Water Availability(= P + SWin) for each of 308 HUC-12’s of the Conn. Riverwatershed (mean annual) Map by Sara Brandt, using regional hydrologic equations of Vogel and Wilson (1996) Paper on hydroclimatic regimes to appear as Weiskel, Vogel and others, in preparation, 2007

  11. Now, lower case denotes the normalized water balance: p + (swin + gwin) = et + (swout + gwout) = 1- Land-atmosphere fluxes (P, ET) - Landscape fluxes (GW, SW) hydro- system

  12. Map of Potential Water Availability for the African Continent From MS Thesis by Sara Freeman Tufts University 2007

  13. Hydroclimatic regime plotShows relative magnitudes of vertical and horizontal fluxes Deerfield River, MA, HUC-12

  14. headwaters humid very humid sub-humid = p ConnecticutRiver basin, hydroclimatic regimes (for 308 HUC-12’s) ET / P Very humid 0 – 0.33 Humid 0.33 – 0.66 Sub-humid 0.66 – 1.0 Semi-arid 1.0 – 1.5 Arid 1.5 – 3.0 Very arid > 3.0 (data compiled by S.. Brandt using Vogel et al regressions) semi-arid hydroclimatic pathway arid very arid mouth = et

  15. Integrating human water useinto the water balance … SWin + P + Hin = SWout + ET + Hout (see Weiskel and others, 2007) Hout = withdrawals Hin = return flows + imports

  16. A new conceptual model of the terrestrial water balance: …a water balance with three flux classes:- Land-atmosphere fluxes (P, ET) - Landscape fluxes (GW, SW) - Human fluxes (Hin, Hout) hydro- system

  17. Water-use Regimes: 4 end-member (EXTREME) regimes Central Valley Aquifer Hin Hin Hout P - ET P - ET SW + GW churned surcharged Hout P ET P - ET SW + GW SW + GW undeveloped depleted (from Weiskel, Vogel and others 2007)

  18. Water-use regime plotShows relative magnitudes of withdrawals versus return flows and of human vs. natural fluxes.(Weiskel, Vogel and others, 2007)

  19. Selected Water-Use RegimesWatersheds From Weiskel, Vogel and others., 2007 Normalized Imports +Return Flows Normalized Withdrawals

  20. Selected water-use regimesAquifers From Weiskel, Vogel and others., 2007 Normalized Return Flows Normalized Withdrawals

  21. Seasonal (Monthly) Water Use Regimes Upper Charles River Aquifer, Massachusetts 1989-1998 Regimes are sensitive to seasonal climate and water use variations Based on transient simulations of Eggleston (2003) Normalized Return Flows Normalized Withdrawals

  22. A Water Resource Development Pathway Mississippi River Alluvial Aquifer, Predevelopment 1918 to 1998 Water use regimes are subject to trends Based on transient simulations of Reed (2003) Normalized Return Flows Normalized Withdrawals

  23. Sustainable Water-Use Regimes A rich topic for future research For example relative Net demand RND RND>0.2 implies STRESS Constant RND Normalized Return Flows Normalized Withdrawals

  24. Green Water Management Potential Green water management strategies are most attractive in hydrologic units with high water use intensity AND high green water availability

  25. An Indicator of Green Water Management Potential From MS thesis Sarah Freeman Tufts University 2007

  26. Summary • Traditional focus has been on net water balance of watersheds • Focus was onblue-waterdemands of humans and aquatic ecosystems • Traditional water assessments did not fully incorporate humans into the water balance • Focus was on watersheds, whereas water availability also depends upon location WITHIN watershed • Total water balance of hydrologic units offers a more comprehensive view of hydroclimatology

  27. Summary • Water Resource Assessments Must Focus on Hydrologic Units (HU’s) and total water balance because: • 1- Total water balance focuses on blue and green- water demands of humans (e.g., rainfed agriculture) and terrestrial ecosystems • 2-Water is managed in hydrologic units • 3- Spatial datasets are gridded which is consistent with HU’s • 4-Integrated water balance is needed for full incorporation of humans into water cycle

  28. Climate Elasticity of Streamflow Sankarasubramanian, Vogel and Limbrunner, Climate Elasticity of Streamflow in the United States, Water Resources Research, 2001.

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