Assessing Residential Water Supply Demand Changes

for the City of Long Beach Under Climate Change Scenarios

City of Long Beach Climate Resiliency AssessmentLoyola Marymount

UniversityJeremy S. Pal

Brianna R. PaganChengyu Gao

March 2016

Introduction• Part of City of Long Beach Climate Resiliency

Assessment Report• Proposed by Mayor Robert Garcia in his January 2015

State of the City address• This study focuses on:• Local water demand changes• Residential irrigation• Drought analysis in the past and future

• Time frame: 1966-2005, 2011-2050

Population Changes•Population growth from census data:•0.01% growth from 2000 to 2010•0.46% growth from 2010 to 2015

•Average change of 0.16% is used for population projection

2015 2020 2025 2030 2035 2040 2045 2050455,000

460,000

465,000

470,000

475,000

480,000

485,000

490,000

495,000

500,000

505,000

Long Beach City Population Growth vs. Year

Year

Popu

latio

n

Outdoor Irrigation Demand Quantification• Basic Model – runoff calculation

• Data Sources:• California Irrigation Management Information System (CIMIS)

(1990-2015)• Ten coupled atmosphere-ocean global climate models

(GCMs) (1966-2005)• Projection:• Representative Concentration Pathway 8.5 (RCP 8.5) (2011-2

050)• Parameters:• Precipitation, evaporation, temperature

Residential Landscape Area Estimate• Residential homes are broken into three categories:• Single Family Homes• Duplexes• Multiple Family Homes

• Geographic Information System (GIS) is used to find the total parcel area of residential homes• Zoning data dictionary is provided by the Long Beach city

website• Residential landscape area is estimated by random

sampling of 100 homes

Single-Family Homes

Duplexes Multiple-Family Homes

Total Parcel Area (ft2) 400,000,000 65,000,000 83,000,000Number of Parcels 56,000 10,000 6,300

Average Parcel Area (ft2) 7,300 6,200 13,000Average Landscape Size

(ft2)2,100 2,000 1,600

Fraction of Landscape Area to Average Parcel

Area

28.4% 31.7% 8.5%

Total Rooftop Area (ft2) 120,000,000 26,000,000 28,000,000Number of Rooftops 72,000 15,000 10,000

Finalizing Quantification• Model Correction include parameters below:• Crop Coefficient (Kc)• Effective Evapotranspiration (ET0)• Effective Precipitation (Pe)• Storm Water Capture (SWC)

• Corrections return effective runoff (Runoffe)• The annual residential irrigation demand (ID):

Total Demand Change Estimate• Water consumption of Long Beach in 2014:• 112 gallons per capita per day (GPCD)

• After city’s water conservation effort, it is estimated that the water consumption will likely be reduced to 100 GPCD• Water consumption will be fixed at 100 GPCD in the

projected period of 2030-2050• Population growth is incorporated in the projection

Conclusion• Further reduction beyond Long Beach Water

Department’s (LBWD) 100 GPCD goal will be difficult to achieve• Population growth has the potential to exceed further

GPCD reduction, resulting a net increase in water usage• Storm water capture (i.e. equipping rain barrels with

residents) will not significantly impact water demand• Large scale drought tolerant conversions could save

Long Beach an additional 2030 acre-feet per year under a warmer climate