WEAP Model Development in California Water Plan Mohammad Rayej, Ph.D., P.E. Senior Engineer, W.R. California Dept. of Water Resources

Goals (General) Recommendations from CWP Update’ 05 Improve Quantitative analysis –Historical Water Portfolios –Future Scenarios –Alternative Response Packages

Goals (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: 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 Water Plan’ 09 (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 view (10 hydrologic Regions)

Demand 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 & Supply (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 view (Urban indoor & outdoor disaggregation)

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 (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 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 Projection Urban Outdoor Outdoor land use projection ( ) –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 ( ) –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 (Scenario Drivers) Population –3 population scenarios driving Ag land use (acre) Climate –12 climate scenarios driving “unit” water use rates (ft)

Ag Demand (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 view (Ag physical parameters)

WEAP data view (Ag climate parameters)

Environmental Demand Projection (Approach) Historical “unmet demand” –Historical “actual” applied water data ( ) 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. ( 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 (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 –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 ( )

Demand Scenarios (General) Demand Scenarios (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 Scenarios (scenario manager)

Ag Demand Projection (TAF) ( Sac HR, ) (3 scenarios, climate # 1)

Urban Indoor Demand Projection (TAF) (Sac HR, ) (3 scenarios)

Urban Outdoor Demand Projection (TAF) (Sac HR, ) (3 scenarios, climate #1)

Environmental Demand Projection (additional desired flow, TAF, ) (Sac HR, 3 scenarios, climate #1)

Next 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, …)