WHERE AND WHEN DO WE WHERE AND WHEN DO WE NEED WATER? NEED WATER?

Dr. Francisco J. MezaDr. Francisco J. MezaProject MentorProject Mentor

Dr. Guillermo PodestáDr. Guillermo Podestá

Facultad de Agronomía e Ingeniería ForestalFacultad de Agronomía e Ingeniería ForestalPontificia Universidad Católica de Chile Pontificia Universidad Católica de Chile

ObjectivesObjectives

Main objective: Main objective: Characterize the main components of the agricultural Characterize the main components of the agricultural hydrological cycle as well as the possible crop yield hydrological cycle as well as the possible crop yield outcomes of irrigated sectors under ENSO scenarios. outcomes of irrigated sectors under ENSO scenarios.

Specific objectives were:Specific objectives were:– ENSO impacts on the water cycle and crop growth. ENSO impacts on the water cycle and crop growth. – Probability distribution functions of potential and actual Probability distribution functions of potential and actual

evapotranspirationevapotranspiration– Identify regions and seasons that are particularly sensitive to water Identify regions and seasons that are particularly sensitive to water

scarcityscarcity– Perform preliminary estimates of the benefits of using climate Perform preliminary estimates of the benefits of using climate

forecasts in agricultural water resources planning.forecasts in agricultural water resources planning.

Region Under StudyRegion Under StudyMaipo River Basin Maipo River Basin

Climatic Variability in Chile and El NiClimatic Variability in Chile and El Niño ño PhenomenonPhenomenon

Mean Annual Precipitation (1950-1999) at six Chilean Localities

Locality Locality Lat (S)Lat (S) El NiEl Niññoo NormalNormal La NiLa Niññaa

PudahuelPudahuel 33.2333.23 412.9412.9 217.8217.8 231.0231.0

Curicó Curicó 34.5834.58 1003.81003.8 589.9589.9 612.3612.3

Concepción Concepción 36.4636.46 1513.81513.8 1091.51091.5 1095.71095.7

Temuco Temuco 38.4638.46 1258.01258.0 1087.91087.9 1116.91116.9

Valdivia Valdivia 39.3839.38 2237.92237.9 1946.31946.3 1983.01983.0

Puerto Montt Puerto Montt 41.2641.26 1765.41765.4 1719.51719.5 1806.41806.4

Climatic Variability in Chile and El NiClimatic Variability in Chile and El Niño ño PhenomenonPhenomenon

In central Chile, ENSO does have an influence on other In central Chile, ENSO does have an influence on other meteorological variables that play a fundamental role on meteorological variables that play a fundamental role on

reference evapotranspiration (Meza, 2005)reference evapotranspiration (Meza, 2005)

0

0.2

0.4

0.6

0.8

1

1.2

130 150 170 190 210

ETo (mm)

P(X

<x) EN

LN

N

Water DemandsWater Demands

Surface of crops was determined in each Surface of crops was determined in each section of the basin based on the Chilean section of the basin based on the Chilean Agricultural CensusAgricultural Census

Crop Potential ET was calculated using Crop Potential ET was calculated using FAO crop coefficientsFAO crop coefficients– ETp = Kc * EToETp = Kc * ETo

Irrigation was triggered ony when soil Irrigation was triggered ony when soil water budget fell below a threshold level water budget fell below a threshold level

Soil Water Balance AlgorithmSoil Water Balance Algorithm

max1max1

max1

11

1

12

)(

0

1.0

RPpRPp

RPpD

PpR

ETp

ETpETa

DRETaPp

cc

c

ENSO Effect on Water Demands in ENSO Effect on Water Demands in Central ChileCentral Chile

Water Demands in the Maipo River Basin

0

50000

100000

150000

200000

250000

300000

350000

400000

450000

La Niña Normal El Niño

m3 *1

000 La Niña

Normal

El Niño

ENSO Forecats for Water Resurces ENSO Forecats for Water Resurces ManagementManagement

In Chile, basins are regulated by the “Water In Chile, basins are regulated by the “Water Code Bill”Code Bill”

There are water rights that guarantee There are water rights that guarantee specific amouts to the holders. This limits specific amouts to the holders. This limits the possibility of allocating water according the possibility of allocating water according to the demand (i.e. conditioned on ENSO)to the demand (i.e. conditioned on ENSO)

Only in a situation of severe water scarcity it Only in a situation of severe water scarcity it will be possible to use climatic-oceanic will be possible to use climatic-oceanic indicesindices

Getting the right frameworkGetting the right framework

Up to this moment the objectives were achieved Up to this moment the objectives were achieved – ENSO does play a role determining different ENSO does play a role determining different

evapotranspiration ratesevapotranspiration rates– Greater demands are observed in the second section Greater demands are observed in the second section

(“where”) and during La Niña years (“when”)(“where”) and during La Niña years (“when”)– Due to regulatory issues the real decision maker for Due to regulatory issues the real decision maker for

water allocation is the farmer not the local authoritywater allocation is the farmer not the local authority

Can farmers take advantage of ENSO information Can farmers take advantage of ENSO information for irrigation management? for irrigation management?

Use of ENSO driven climatic Use of ENSO driven climatic information for optimum water information for optimum water

allocation allocation International Workshop on Climate Prediction and

Agriculture: Advances and Challenges. May 9-13, 2005.

Dr. Francisco J. MezaDr. Francisco J. Meza

Facultad de Agronomía e Ingeniería ForestalFacultad de Agronomía e Ingeniería ForestalPontificia Universidad Católica de Chile Pontificia Universidad Católica de Chile

Droughts in ChileDroughts in Chile

Occurrence of Severe DroughtsOccurrence of Severe Droughts

Source: Urrutia de Hazbun et al, 1993.Source: Urrutia de Hazbun et al, 1993.

Year Affected Regions ENSO phase (Trenberth)1960-1962 IV Normal

1965 IV, V La Niña1967 IV , V , RM Normal

1968-1969 III, IV, V, RM , VI El Niño1970-1971 III, IV La Niña

1979 VIII, IX, X Normal1985 IV La Niña

1990-1991 III, IV, V Normal1998 V, RM, VI, VII, VIII La Niña

Mean Economic Impact of Droughts in Mean Economic Impact of Droughts in Chile Chile (Source: MOP-UC, 1997)(Source: MOP-UC, 1997)

05000

1000015000200002500030000

7 13 18 22 26 30 34 38 42 46

Unidad de Análisis

M$/

Añ

o

Basin Number

Can we take advantage of ENSO Can we take advantage of ENSO information for water resources information for water resources

management problems?management problems?

Requisites of valuable information Requisites of valuable information (ENSO forecast)(ENSO forecast)

Climatic Predictability + Systems Vulnerability

+ Decission Capacity

Hansen, J.W., 2002

Climatic PredictabilityClimatic Predictability(ENSO Forecast)(ENSO Forecast)

Irrigation ManagementIrrigation Management

When water is not a limiting factor, irrigation is reduced to When water is not a limiting factor, irrigation is reduced to the management of the soil water budget to minimize plant the management of the soil water budget to minimize plant stress. stress.

When water is scarce the operation of irrigation increases When water is scarce the operation of irrigation increases in complexity, becoming a traditional resource allocation in complexity, becoming a traditional resource allocation problem.problem.

Optimum allocation of resources is achieved when the Optimum allocation of resources is achieved when the consequences associated to all possible combinations of consequences associated to all possible combinations of alternatives and states of the variable are known.alternatives and states of the variable are known.

Traditional ApproachTraditional Approach

Assumes that Water Demands are constant (i.e. Assumes that Water Demands are constant (i.e. fixed at climatological values)fixed at climatological values)

Uses Doorenbos and Kassam empirical equations Uses Doorenbos and Kassam empirical equations or Jensen´s formula to estimate yield changes as a or Jensen´s formula to estimate yield changes as a function of actual evapotranspiration function of actual evapotranspiration

4

1

n

i

i

j

jm ETc

ETa

Y

Jensen´s formula (Jensen, 1968)

Traditional ApproachTraditional Approach

Mathematical programming formulationMathematical programming formulation

lmlmlmXl

QETcEXc ,;max ,,,

M

mmm YP

1

*)(

lm

ml QX ,

ml

X ml

,

0,

Objective Function

Constraints

ENSO based ApproachENSO based Approach

Since ENSO does influence reference Since ENSO does influence reference evapotranspiration, it is reasonable to incorporate evapotranspiration, it is reasonable to incorporate that information and perform an optimization that information and perform an optimization conditioned on ENSO phaseconditioned on ENSO phase

The problem is rewritten asThe problem is rewritten as

lmlmlmXl

QoETcEXo ,|;max ,,,

Where o represents El Niño, Normal or La Niña phase

Expected Value of InformationExpected Value of Information

The information (ENSO forecast) will be The information (ENSO forecast) will be valuable if valuable if at least one of the optimal actions at least one of the optimal actions (i.e. irrigation strategies) associated with the (i.e. irrigation strategies) associated with the forecast information differs from the one forecast information differs from the one selected without forecast.selected without forecast.

According to Bayes´ theorem one can According to Bayes´ theorem one can calculate the expected value of information calculate the expected value of information as:as: coPoEVI

o

)(*

Case StudyCase StudyMaipo River BasinMaipo River Basin

Parameters usedParameters used

CropTomato Potato Watermelon

Price USD/ton 250 220 320Ym (ton) 65 50 401 0.33 0.37 0.622 1.15 0.74 0.743 0.74 0.62 0.744 0.33 0.15 0.24

ResultsResults

Expected Value of Information for the different Expected Value of Information for the different phases of ENSO phases of ENSO

Available water at each irrigation time was equivalent to 55 mm Available water at each irrigation time was equivalent to 55 mm

0

50

100

150

200

250

300

350

La Niña Normal El Niño

EV

I (U

SD

/ha)

____

ResultsResults

Expected Value of Information as a function of Expected Value of Information as a function of different levels of water supplydifferent levels of water supply

-50

0

50

100

150

200

250

0 20 40 60 80 100 120 140 160 180 200

Available Water for Irrigation (mm)

EV

I (U

SD

/ha)

___

ResultsResults

So far results show that ENSO information can be used to So far results show that ENSO information can be used to select an irrigation strategy, representing a case of perfect select an irrigation strategy, representing a case of perfect information (i.e. the forecasted evapotranspiration is equal information (i.e. the forecasted evapotranspiration is equal to the observed one in susequent periods)to the observed one in susequent periods)

A more realistic approach should be a case where A more realistic approach should be a case where irrigation strategy is revised based on irrigation strategy is revised based on – a) Previous water demandsa) Previous water demands– b) Forecasted evapotranspirationb) Forecasted evapotranspiration

In that situation the decision maker can correct “wrong” In that situation the decision maker can correct “wrong” allocations due to climate variability allocations due to climate variability

ResultsResults Evolution of the objective function Evolution of the objective function of the decision maker that of the decision maker that

allocates water using El Niño forecasts and the one that allocates water using El Niño forecasts and the one that bases his decision on historical ETc valuesbases his decision on historical ETc values

14300

14350

14400

14450

14500

14550

14600

14650

14700

14750

14800

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Irrigation Moment

Obje

ctiv

e Funct

ion (U

SD

)___

__

Revised Strategy ENSO Forecast

Value of Forecast

Conclussions and Future StepsConclussions and Future Steps

In locations where ENSO signal has an effect on In locations where ENSO signal has an effect on water demands there is an economic potential for water demands there is an economic potential for climate forecasts in water resources allocation at climate forecasts in water resources allocation at the farm level.the farm level.

The expected value of information is not a The expected value of information is not a monotonic function because when water is very monotonic function because when water is very scarce the allocation decissions are limitted.scarce the allocation decissions are limitted.

The next step is to refine the translation of yields The next step is to refine the translation of yields because they also are affected by climatic because they also are affected by climatic variability (use process based crop simulation variability (use process based crop simulation models) models)

Where and When do we Need Where and When do we Need Water?Water?

Summary of Scientific ActivitiesSummary of Scientific Activities √√ Regional Water Demand Model Conditioned on ENSO Regional Water Demand Model Conditioned on ENSO

phasesphases √√ Assessment of potential use of ENSO information for Assessment of potential use of ENSO information for

Irrigation ManagementIrrigation Management √√ Communication and DisseminationCommunication and Dissemination

– 84th AMS Annual Meeting, Seattle Washington84th AMS Annual Meeting, Seattle Washington– Local Seminar Local Seminar “Climatic Variability and Change: Issues in Water “Climatic Variability and Change: Issues in Water

Resources, Agriculture and Forest Ecosystems”Resources, Agriculture and Forest Ecosystems” Dr Carlos Nobre, CPTECDr Carlos Nobre, CPTEC Dr Bonifacio Fernandez. School of EngineeringDr Bonifacio Fernandez. School of Engineering Dr Francisco Meza. ATI participantDr Francisco Meza. ATI participant

Summary of Scientific ActivitiesSummary of Scientific Activities

– 85th AMS Annual Meeting, San Diego, California85th AMS Annual Meeting, San Diego, California– Papers:Papers:

Meza, F.J. 2005. Use of ENSO driven climatic information for Meza, F.J. 2005. Use of ENSO driven climatic information for optimum irrigation under drought conditions: Preliminary optimum irrigation under drought conditions: Preliminary assessment based on model results. Climate Research: assessment based on model results. Climate Research: submitted.submitted.

Meza, F.J. 2005. Obtaining daily precipitation parameters from Meza, F.J. 2005. Obtaining daily precipitation parameters from meteorological yearbooks. Agricultural and Forest Meteorology: meteorological yearbooks. Agricultural and Forest Meteorology: submitted.submitted.

Meza, F.J. 2005. Variability of reference evapotranspiration and Meza, F.J. 2005. Variability of reference evapotranspiration and water demands. association to ENSO at the Maipo river basin, water demands. association to ENSO at the Maipo river basin, Chile. Global and Planetary Change: In press Chile. Global and Planetary Change: In press

"You don't get points for predicting rain. "You don't get points for predicting rain. You get points for building arks."You get points for building arks."

– – Lou Gerstner, IBM CEO (Quoted by Lou Gerstner, IBM CEO (Quoted by Richard Katz, UCAR)Richard Katz, UCAR)

QUESTIONS????QUESTIONS????