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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
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