WEAP Model Development in WEAP Model Development in California Water PlanCalifornia Water Plan

Mohammad Rayej, Ph.D., P.E.Mohammad Rayej, Ph.D., P.E.Senior Engineer, W.R. Senior Engineer, W.R.

California Dept. of Water ResourcesCalifornia Dept. of Water Resources

GoalsGoals(General)(General)

Recommendations from CWP Update’ 05

• Improve Quantitative analysis

– Historical Water Portfolios– Future Scenarios– Alternative Response Packages

GoalsGoals(Specifics)(Specifics)

• Current and future water Demand & Supply• Demand (Urban, Ag, Environment)• Supply (Surface, GW, Desal, …)

• Future Scenarios• Population growth• Socio_economic factors• Climate Change

• Response Packages • 27 resource management strategies (Demand reduction, supply

augmentation, system re-operation, …)

• Performance Metrics & Evaluation• (water supply, quality & energy benefits, cost, shortages

magnitude, duration and frequency)

Analytical Tool: WEAPAnalytical Tool: WEAP

• Water Evaluation And Planning Model• Integrates Demand & Supply in a single tool• Demand_driven water supply allocation model• Demand priorities and supply preferences• Highly scaleable in space & time• Steps through time to simulate future conditions• Very suitable to build future water scenarios • Explores management strategies (demand

reduction, supply augmentation)

Application to California Application to California Water Plan’ 09Water Plan’ 09

(General Assumptions)(General Assumptions)

• Base year: 2005• Projection year: 2050• Time scale: monthly time step• Space scale: Hydrologic Region, Planning Area

(SR, SJ)• Regions not linked• High level representation of Regions (actual

water system; reservoir operations not modeled)

10 Hydrologic Regions 10 Hydrologic Regions

• 1- North Coast• 2- San Francisco Bay• 3- Central Coast• 4- South Coast• 5- Sacramento River • 6- San Joaquin River• 7- Tulare Lake• 8- North Lahontan• 9- South Lahontan• 10- Colorado River

WEAP Schematic viewWEAP Schematic view(10 hydrologic Regions)(10 hydrologic Regions)

Demand Methods in WEAPDemand Methods in WEAP 1- Rainfall-Runoff “Catchment” Method (Green dots !!!)

• Approach:– Uses so called “2-bucket” approach to perform soil moisture mass balance in

the root zone and deep percolation over time– Physically based; includes soil, plant and climate and irrigation parameters– Computes crop ET, surface runoff, subsurface lateral flow to surface stream,

deep percolation to GW. – Very suitable for climate change scenarios

• Input Parameters:– Plant (land use area, Kc, leaf area index to control surface runoff)– Soil (soil moisture capacity, soil hydraulic conductivity, initial moisture content)– Climate (precip, temp, RH, wind speed, melting point and freezing point

temperature for snowmelt runoff and snowpack accumulation)– Irrigation (low and high threshold of soil moisture to start or stop irrigation)

• Output:– Demand volume (Acre-ft)

Demand & SupplyDemand & Supply(status)(status)

• Demand (development and calibration completed)

– Ag– Urban (Indoor & Outdoor)– Environment

• Supply sources (in progress)– SWP, CVP, GW, Local projects, Desalination, Imports– Projection Approach: “Water Year Type” method based on

Precip, using historical supplies and precip tied to future precip from climate scenarios

Urban Demand

– Urban Indoor - Urban Outdoor

• Single Family - Single Family• Multi Family - Multi Family• Commercial - Commercial• Industrial - Large

Landscape

WEAP data viewWEAP data view(Urban indoor & outdoor disaggregation)(Urban indoor & outdoor disaggregation)

Urban Demand Method Urban Demand Method

Per Capita Approach (Indoor)

- Unit water use rate: “Unit” water use rate (e.g. AF/person, AF/Homes)

- Total activity level: Total level of activity for the demand category (People, Homes)

- Demand Volume = Unit rate x Total Activity Level

Urban Demand Urban Demand (Scenario Drivers)(Scenario Drivers)

– 3 Growth Scenarios (affecting activity level)

• Population• Single Family homes• Multi Family homes• Commercial employees• Industrial employees

– Elasticity factors (affecting per capita use rate)• Price of water• Average household income• Number of people in SF homes (Indoor demand only)• Number of people in MF homes (Indoor demand only)• Naturally Occurring conservation

– Climate factors (Urban Outdoor)

Urban Demand MethodUrban Demand Method

Catchment Approach (Outdoor)

• Physically-based hydrologic process based on soil, plant and climate (precip, temp, ET, surface runoff, deep percolation, seepage)

• Computes Irrigation Demand (e.g. ft)• Irrigation demand adjusted by elasticity factors

(price, family income, NOC)• Urban outdoor irrigated area (e.g. acre)• Demand volume (acre x ft)

Urban Demand ProjectionUrban Demand Projection

• Urban Outdoor

• Outdoor land use projection (2005-2050)

– Historical (WY 2000) data (CIMIS & CUP+) was used to compute Etc, ETAW, AW (ft) assuming cool season/warm season crop coefficients for each region.

– Applied Volume (WY 2000) used to estimate landscape area (Acres)– Future demographic projection is used to drive future outdoor

landscape;

• Climate data projection on Urban outdoor (2005-2050)– Like Ag land climate projection, the 12 future climate projection on

Urban areas downscaled on the 10 hydrologic regions were provided by David Yates (NCAR)

Ag Demand Ag Demand (Scenario Drivers)(Scenario Drivers)

• Population – 3 population scenarios driving Ag land use

(acre)

• Climate– 12 climate scenarios driving “unit” water use

rates (ft)

Ag DemandAg Demand(physical parameters in WEAP)(physical parameters in WEAP)

• Soil• Soil moisture capacity• Hydraulic conductivity• Initial soil moisture

• Plant• Crop coefficient (Kc)• Leaf Area Index (crop canopy to control surface runoff)

• Climate• Precip• Temp• Relative Humidity• Wind Speed• Lattitude• Melting point temp (snowmelt runoff)• Freezing point temp (snowpack accumulation)

• Irrigation• Lower soil moisture Threshold (LT) (to start irrigation)• Upper soil moisture Threshold (UT) (to stop irrigation)

WEAP data viewWEAP data view(Ag physical parameters)(Ag physical parameters)

WEAP data viewWEAP data view(Ag climate parameters)(Ag climate parameters)

Environmental Demand Projection Environmental Demand Projection (Approach)(Approach)

• Historical “unmet demand”– Historical “actual” applied water data (1998-2007) was

compared with environmental Objectives to determine “unmet” demand.

– Unmet demands were ranked from min. to max. to find “percentiles” (min.,25,50,75,max).

– Percentiles were used to assign “Year Type” class, e.g. (<min=critical, 25%=Dry, 50%=Below Normal, 75%=Above Normal, >75%= Wet)

– Within each “Year Type” class, “min”, “avg”, “max” values were used to assign to 3 narrative Expansive, Current Trend and BluePrint scenarios, respectively. This implies environmental water is limited under Expansive growth scenario, while BluePrint growth has more access.

Environmental Demand Projection Environmental Demand Projection (Approach)(Approach)

• Future “additional desired flow”– Then, future climate scenario for each region was

used to generate a corresponding “Percentile” and “Year Type” classification based on future Precip for the projection period of 2005-2050.

– Finally, future annual “Precip” Year Type, was matched with historical “Unmet” demand Year Type class to find corresponding “additional desired flow” in respective future years when WEAP steps through time (2005-2050)

Demand ScenariosDemand Scenarios(General)(General)

• 3 Growth Scenarios

Current Trends Growth – Current trend of population growth projected by DOF

Strategic Growth – Low population growth projection by PPIC

Expansive Growth – High population growth projection by PPIC

• 12 Climate Scenarios– Based on 2 emission scenarios (A2 and B1) projections in

Governer’s report simulated by 6 GCM models.

WEAP ScenariosWEAP Scenarios(scenario manager)(scenario manager)

Ag Demand Projection (TAF)Ag Demand Projection (TAF)((Sac HR, 2005-2050)Sac HR, 2005-2050)

(3 scenarios, climate # 1)(3 scenarios, climate # 1)

Urban Indoor Demand Projection (TAF)Urban Indoor Demand Projection (TAF)(Sac HR, 2005-2050)(Sac HR, 2005-2050)

(3 scenarios)(3 scenarios)

Urban Outdoor Demand Projection (TAF)Urban Outdoor Demand Projection (TAF)(Sac HR, 2005-2050)(Sac HR, 2005-2050)

(3 scenarios, climate #1)(3 scenarios, climate #1)

Environmental Demand Projection Environmental Demand Projection (additional desired flow, TAF, 2005-2050)(additional desired flow, TAF, 2005-2050)

(Sac HR, 3 scenarios, climate #1)(Sac HR, 3 scenarios, climate #1)

Next Steps in WEAPNext Steps in WEAP

• Develop baseline future supply

• Determine future level “unmet” demands under the 3 Demand (Growth) Scenarios.

• Develop Response Packages from the list of 27 Resource Management Strategies.

• Evaluate Response Packages in terms of a set of performance metrics (water supply benefits, costs, …)