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Civil & Environmental Engineering Princeton University
Network Analysis of Virtual Water Trade Megan Konar
From space, Earth is a “Blue Planet”
Global DistribuKon of Water on Earth
Water available for plant use is less than 0.34% of all fresh water
Global DistribuKon of Water on Earth
FROZEN 70%
UNDERGROUND 30%
SURFACE WATER 0.34%
FRESH WATER 3%
OCEANS 97%
Water for Food Water and food security are inextricably linked. Water and food systems face increasing pressures from global populaKon growth, economic development, and climate change. How are water and food systems linked through internaKonal trade?
Sources of Water
Blue Water
Green Water
The vast majority (80%) of irrigaKon (i.e. “blue”) water resources goes to agriculture. Most food (60-‐70%) is actually rainfed, or produced using “green” water resources.
HarvestingCotton plant Seed-cotton
Cotton seed
Cotton lint
Cotton seedcake
Cotton seed oil
Grey fabric
Fabric
Final textile
Cotton linters
Cotton, notcarded or combed
Cotton, carded orcombed (yarn)
Hulling/extraction
Garnetted stock
Carding/Spinning
Yarn waste
Knitting/weaving
Wet processing
Finishing
Cotton seed oil,refined
Ginning
18.063.0
82.035.0
47.016.0
33.051.0
20.010.0
00.107.1
00.100.1
99.095.0
10.005.0
00.100.1
00.100.1
99.095.0
10.005.0
82.035.0
Legend
Value fraction
Product fraction
ProducKon Chain Co`on
Hoekstra, 2009
Hoekstra, 2009
Crop Water Use Varies In Both Space and Time
H08 Global Hydrologic Model ½₀ x ½₀ SpaKal ResoluKon
Hanasaki, 2010
Virtual W
ater Con
tent [-‐]
Water, Food, and Trade The water embodied in the internaKonal food trade is referred to as “virtual water trade”. Virtual water trade is driven by underlying economic system and climaKc factors.
Water, Food, and Trade The water embodied in the internaKonal food trade is referred to as “virtual water trade”. Virtual water trade is driven by underlying economic system and climaKc factors. This complex system can be represented as a network.
NODES: Countries parKcipaKng in internaKonal food trade. LINKS: Weighted by water volumes, directed by trade.
What is a network?
…Quick Intro
Unweighted & Undirected Weighted & Undirected
Unweighted & Directed Weighted & Directed
Node
Link
4
2
1 8
4
6
1
2
3
Network ProperKes Undirected Directed
Degree Strength
k = 2
k out = 0 k in = 1
s = 7
2
1 4
6
s out = 3 s in = 10
Network ProperKes Unweighted Weighted
Nearest Neighbor Clustering
Virtual Water Trade Network
Regional Networks
Crops and Livestock Crops Livestock All Water Green Water Blue Water
Regional Networks
Crops and Livestock Crops Livestock All Water Green Water Blue Water
Regional Networks
Crops and Livestock Crops Livestock All Water Green Water Blue Water
EnKre network is driven by the trade of rain-‐fed crops
Network ProperKes Node Degree
Node Strength
k out = 0 k in = 1
2
1 4
6
s out = 3 s in = 10
ExponenKal export degree distribuKon
Stretched-‐exponenKal strength distribuKon
Data Fit
Power Law RelaKonship Volume of virtual water traded vs. number of trade partners follows a power law relaKonship
This relaKonship is parKcularly strong for food import, indicaKng that the more import trade partners a country has, the much more virtual water it imports.
Data Fit
Evidence of Rich Club Nearest-‐Neighbor Degree Clustering Coefficient
Weights break down disassortaKve structure
Unweighted Weighted
Unweighted Weighted
Network Dynamics Over Time
% Change from
1986
1986 2007
Volume of virtual water embodied in trade has more than doubled from 1986-‐2007, parKcularly for green water.
Green Water
Blue Water
Dalin et al, 2012; Konar et al, In Review
Global Water Savings from Trade
Savings = 238 km3 yr-‐1 Equivalent to 9% of global agricultural water use
Dalin et al, 2012
Blue and Green Networks Save Water Glob
al W
ater Savings [m
3]
<VW
C Ga
p>
Pos. Links [%
] Crop
Trade
[%]
What is driving this increased water saving over Kme?
. Blue Water Green Water .
IntensificaKon of Trade on Water-‐Efficient Links
. Blue Water Green Water .
QuesKons?
Thank You