1Monthly water stress: The relevance of temporally explicit water impact assessment in global crop production

Stephan Pfister and Peter Bayer

ETH Zurich, Institute for Environmental Engineering, Ecological Systems Design Group

Email contact: pfister@ifu.baug.ethz.ch

LCA XIII, Orlando, October 1, 2013

2 So far annual water stress factors with global coverage available Monthly water scarcity factor from WFN (Mekonnen et al. PLOS 2011) has

factors for 405 major watersheds

No data for Italy and many other arid areas

Linear relation with consumption-to-availability

This work is based on annual water stress index (WSI) (Pfister et al. ES&T 2009)

Scaling from 0.01 to 1 (water deprivation factor)

Applied in several LCA studies -> experience of application

Overview water stress assessment (characterization factors)

3 So far only annual water stress factors with global coverage available (based on water use to availablility) Monthly water scarcity factor from WFN (Mekonnen et al. PLOS 2011) has

factors for 405 major watersheds

No data for Italy and many other arid areas

Linear relation

This work is based on annual water stress index (WSI) (Pfister et al. ES&T 2009)

Scaling function (0.01 to 1) (water deprivation factor)

Applied in several LCA studies -> experience of application

Overview water stress assessment (characterization factors)

4Deriving monthly WSI

*9.81

0.01

1

1 1monthlymonthly WTA

WSIe

*monthly monthly year

WTA WTA GSD

Withdrawal-to-availability (WTA) based Annual Watergap 2 (Alcamo et al. 2003)

Monthly adjustments based on Vorosmarty et al. (2000)

Include inter-annual precipitation variability:

geometric standard deviation (GSDyear) for 30 years

Adjust annual WSI function (exclude factor for monthly precipitation variability)

was -6.4

5Annual WSI

6WSI January

7WSI February

8WSI March

9WSI April

10

WSI May

11

WSI June

12

WSI July

13

WSI August

14

WSI September

15

WSI October

16

WSI November

17

WSI December

18

Monthly WSI of selected rivers

NileWSI

19

Average monthly vs. annual WSI

Original WSI

Average monthly WSI

20

Use weighted monthly vs. annual WSI

Original WSI

Weighted monthly WSI

21

Ratio weighted monthly vs. annual WSI

Monthly resolution reveals higher stress in many watersheds

Weighted monthly

/ annual WSI

< 0.5

0.5-1

1-2

>2.0

Original WSI

Weig

hte

d m

on

thly

WS

I

22

Crop water footprint

Water consumption (WC):160 crops on monthly and 5 arc minutes spatial resolution (Pfister et al. ES&T 2011)

Water footprint (WFP):

( )

mon i i

i

year i annual

i

WFP WC WSI

WFP WC WSI

23

Water footprint of a region

Marginal vs. average impact

24

Water footprint of a region (all crops)

Monthly

Annual

25

Conclusions

Temporal resolution is relevant Mainly for foreground process (global picture does merely change)

Crop choice / plantation dates

Annual use-weighte average maps (sector-specific) For background processes (incl. uncertainty)

Storage effects /residence time Dams

Groundwater stocks Water source (ground surface water) -> different impacts!

Include spatial & temporal resolution induced uncertainty (variability induced)

26

stephan.pfister@ifu.baug.ethz.ch

www.ifu.ethz.ch/ESD

THANKS FOR YOUR ATTENTION!

Paper submitted to J Clean Prod

Characterization maps are published on:http://www.ifu.ethz.ch/ESD/downloads/

27

BACKUP SLIDES

LCA Food 2012 , Saint-Malo, October 2, 2012

28

EuropeJanuary February

July August

April

November DecemberOctober

March

May June

September

29

Avera

ge

ww

(WS

I mon)

WSIyear

Nile Murray Missouri

Nile

Murray

Missouri

Rhone

Rhine

Po

Rhone

Rhine

Po

30

UNCERTAINTY WSI (PFISTER & HELLWEG 2011)

31

Pfister et al 2009: Water Stress Index (WSI)

Includes:

Withdrawal-to-availability (WTA)

Variability in precipitation (VF) = geometric standard deviation (GSD)

Flow regulation (highly regulated = SRF)

Index following logistic function:

31

*

-

VF WTA for SRFWTA

VF WTA for non SRF

*6.4 1

0.01

1

1 1WTAWSI

e