Scenarios for agricultural water demand :Scenarios for agricultural water demand :Experiences from WADI and other projectsExperiences from WADI and other projects

Dr Keith Weatherhead Dr Keith Weatherhead

Institute of Water and EnvironmentInstitute of Water and EnvironmentCranfield University at Silsoe, UKCranfield University at Silsoe, UK

Agricultural Water DemandAgricultural Water Demand

major water use in many European catchments

concentrated in driest areas

peaks in driest months of driest years

mainly consumptive

A simple demand model:A simple demand model:

Demand is sum of products of:

crop areas (ha)

proportions irrigated (%)

irrigation needs (mm per annum)

1/ (irrigation efficiencies)

Dry year irrigation water demand in England

Modelling Future DemandModelling Future Demand

The “IrriGrowth” spreadsheet model was used.

This predicts volumetric water demand at regional level.

Input:

2001 cropping and irrigation data

Socio-economic scenario changes

Climate change impacts on irrigation need

GLOBALISATION

REGIONALISATION

COMMUNITYCONSUMERISM

GLOBALSUSTAINABILITY

LOCALSTEWARDSHIP

PROVINCIALENTERPRISE

WORLD MARKETS

CONVENTIONALDEVELOPMENT

Socio-economic futures

CCDeW: predicted growth in irrigation water demand in England

ProvincialEnterprise

WorldMarkets

GlobalSustainability

LocalStewardship

2025U 34% 14% -20% -4%2025MH 60% 36% -4% 14%

2055U 72% 24% -31% -6%2055MH 117% 56% -13% 19%

% change from 2001 baselineU - unchanged climateMH - medium -high climate change

NB: The forecasts are for unconstrained demand at current costs. Actual use will be constrained by water availability

Some issues raisedSome issues raised

Unconstrained demand or …….?

Market feedback

Increased atmospheric CO2

Adaptation

Sustainability of European Irrigated Agriculture (WADI)

Sustainability of irrigated agriculture in Europe within the context

of the post Agenda 2000 CAP Reforms and the Water

Framework Directive

Led by Julio Berbel, University of Cordoba

Spain.

UK

Italy

Greece

Portugal

Joint Research Centre,

Farmer´s Income Evolution (€/ha)

00.10.20.30.40.5

200 400 600 800 1000 1200 1400 1600

Wat

er P

rice

(€/m

3)

Lezíria do Tejo Baixo Alentejo

Farm income impacts - examples from Portugal

WADI

Labour Demand Curve (h/ha)

0

0.1

0.2

0.3

0.4

0.5

30 60 90 120

Wa

ter

Pri

ce (

€/m

3 )

Lezíria do Tejo Baixo Alentejo

Labour demand impacts -examples from Portugal

WADI

Marginal value of water - examples from England

WADI

Marginal Value of Water £/m3

0

0.5

1

1.5

2

2.5

0 20% 40% 60% 80% 100%

% of unconstrained irrigation water requirements

Mar

gina

l Val

ue £

/m3

Pot/Veg

Pot/S Beet

Which demand?

Market feedback: will crops move? Example of predicted growth in demand in England

Climate change impactsClimate change impacts

Human activity

Climate change

Atmospheric CO2 increase

Stomatal resistanceGrowth rates

Yield

Rainfall & ETTemperature

Frost

Areas irrigatedDepths needed

Locations

Spatial water demand

Atmospheric CO2 increases

Socio-economic scenarios

Future atmospheric COFuture atmospheric CO2 2 increasesincreases

UKCIP02

(ppmv)

Present 2020s 2050s

low 350 422 489

medium-low 350 422 489

medium -high 350 435 551

high 350 437 593

Impacts of increased atmospheric CO2Impacts of increased atmospheric CO2

Impacts are complex and inter-related.

Experimental results generally show:

Faster growth rates, larger plants, higher yield

(typically doubling CO2 increases growth by 30%)

Higher stomatal resistance

In CCDeW, modelling indicated:

direct impacts on irrigation need (mm) cancel out for England

increased yields lead to reduced areas required, reducing water demand

An example of adaptation - An example of adaptation - drip irrigation of potatoes drip irrigation of potatoes

ConclusionConclusion

Modelling agricultural water demand is feasible, but forecasting requires expert

judgement as well as hard science.

Define clearly which “demand” we want.

Must include market feedback loops and iteration.

Must consider farmer adaptation options.

Keith Weatherhead, Cranfield