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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

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

slide2

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
slide3

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

slide4

Background and Motivation IIIBalancing Water for Humans and NaturebyMalin FalkenmarkandJohan Rockström2004

methodology for a national global water census
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.

slide6

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

slide7

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

from watersheds to hydrologic units
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

hydroclimatic regimes 4 extreme end members arise from total water balance
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.)

slide10

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

p sw in gw in et sw out gw out 1 land atmosphere fluxes p et landscape fluxes gw sw

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

slide12

Map of Potential Water Availability for the African Continent

From MS Thesis by Sara Freeman

Tufts University 2007

hydroclimatic regime plot shows relative magnitudes of vertical and horizontal fluxes
Hydroclimatic regime plotShows relative magnitudes of vertical and horizontal fluxes

Deerfield River, MA, HUC-12

slide14

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

integrating human water use into the water balance
Integrating human water useinto the water balance …

SWin + P + Hin

= SWout + ET + Hout

(see Weiskel and others, 2007)

Hout = withdrawals Hin = return flows + imports

slide16

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

water use regimes 4 end member extreme regimes
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)

slide18

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

selected water use regimes watersheds
Selected Water-Use RegimesWatersheds

From Weiskel, Vogel and others.,

2007

Normalized Imports +Return Flows

Normalized Withdrawals

selected water use regimes aquifers
Selected water-use regimesAquifers

From Weiskel, Vogel and others., 2007

Normalized Return Flows

Normalized Withdrawals

slide21

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

slide22

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

slide23

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

slide24

Green Water Management

Potential

Green water management strategies are most attractive in hydrologic units with high water use intensity AND high green water availability

slide25

An Indicator of Green Water Management

Potential

From MS thesis

Sarah Freeman

Tufts University

2007

slide26

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
slide27

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
slide28

Climate Elasticity of Streamflow

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