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Transcript of Tufts University Where Will the Water Go? Hydrologic Impacts of Climate Change David Purkey, SEI and...
Tufts University
Where Will the Water Go?Hydrologic Impacts of Climate Change
David Purkey, SEI and
Richard M. VogelDepartment of Civil and Environmental Engineering
Tufts University
SEI Climate Change SymposiumTufts University
November 30, 2007
Tufts University
• Previous national water resource assessments were completed 30-40 years ago:Wollman and Bonem, 1971; Water Resources Council 1968, 1978National 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
Background and Motivation I
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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
Background and Motivation II
Background and Motivation
III
Balancing Water for Humans and Nature
by
Malin Falkenmarkand
Johan Rockström
2004
Tufts University
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.
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P
Traditionally, water availability is defined in terms of NET water balance of a watershed
P – ET = SWout
* water availability = runoff * reflects both the traditional water-supply perspective, and an aquatic-focused ecological perspective P = Precipitation;
ET = EvapotranspirationSWout = Surface-water runoffAssume that GWin = GWout = 0
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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
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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
headwatersource
headwaterno-flow
terminal flow-through
terminal sink
P P
ET SW + GW
ET
SW + GW
SW + GW
(from Weiskel, Vogel and others., in prep.)
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 regimesto appear as Weiskel, Vogel and others, in preparation, 2007
p + (swin + gwin) = et + (swout + gwout) = 1
- Land-atmosphere fluxes (P, ET) - Landscape fluxes (GW, SW)
hydro- system
Now, lower case denotes the normalized water balance:
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
Deerfield River, MA, HUC-12
ConnecticutRiver basin, hydroclimaticregimes(for 308 HUC-12’s)
ET / PVery humid 0 – 0.33Humid 0.33 – 0.66Sub-humid 0.66 – 1.0Semi-arid 1.0 – 1.5Arid 1.5 – 3.0Very arid > 3.0
(data compiled by S.. Brandt using Vogel et al regressions)
humidvery humid sub-humid
semi-arid
arid
very arid
= et
= p
hydroclimatic pathway
headwaters
mouth
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Integrating human water useinto the water balance …
SWin + P + Hin
= SWout + ET + Hout
(see Weiskel and others, 2007)
Hout = withdrawals Hin = return flows + imports
…a water balance with three flux classes:
- Land-atmosphere fluxes (P, ET) - Landscape fluxes (GW, SW) - Human fluxes (Hin, Hout)
A new conceptual model of the terrestrial water balance:
hydro- system
Water-use Regimes: 4 end-member (EXTREME) regimes
surcharged churned
undeveloped depleted
Hin Hin Hout
SW + GW
SW + GW
SW + GW
(from Weiskel, Vogel and others 2007)
Hout
Central Valley Aquifer
P ET
P - ET P - ET
P - ET
Water-use regime plot
Shows relative magnitudes of withdrawals versus return flows and of human vs. natural fluxes.
(Weiskel, Vogel and others, 2007)
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Selected Water-Use RegimesWatersheds
From Weiskel, Vogel and others., 2007
Nor
mal
ized
Im
por
ts
+R
etu
rn F
low
s
Normalized Withdrawals
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Selected water-use regimesAquifers
From Weiskel, Vogel and others., 2007
Nor
mal
ized
Ret
urn
Flo
ws
Normalized Withdrawals
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Seasonal (Monthly) Water Use Regimes
Upper Charles River Aquifer,
Massachusetts1989-1998
Regimes are sensitive to seasonal climate and
water use variations
Based on transientsimulations of
Eggleston (2003)
Normalized Withdrawals
Nor
mal
ized
Ret
urn
Flo
ws
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A Water Resource Development Pathway
Mississippi River Alluvial Aquifer,
Predevelopment 1918to 1998
Water use regimes are subject to trends
Based on transientsimulations of Reed
(2003)Normalized Withdrawals
Nor
mal
ized
Ret
urn
Flo
ws
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Sustainable Water-Use Regimes
A rich topic forfuture research
For example relative Net demand RND
RND>0.2 impliesSTRESS
out
inout
SW
HHRND
Con
stan
t RN
D
Normalized Withdrawals
Nor
mal
ized
Ret
urn
Flo
ws
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Green Water Management Potential
Green water management strategies are most attractive in hydrologic units with
high water use intensity AND high green water
availability
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Traditional focus has been on net water balance of
watersheds•Focus was on blue-water demands 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
Summary
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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
Summary