impact of climate change on washington metropolitan area ......potential impacts of climate change...
TRANSCRIPT
Potential impacts of climate change on
Washington metropolitan area
water supply
Modeling Quarterly Review Meeting
Chesapeake Bay Program Office, Annapolis, Maryland
July 23, 2013
Sarah Ahmed (with Cherie Schultz, PhD, and Karin Bencala)
Section for Cooperative Water Supply Operations on the Potomac
Interstate Commission on the Potomac River Basin
51 Monroe Street, Suite PE-08 · Rockville, Maryland 20850
Background
Washington Metropolitan Area
Water Supply System Pennsylvania
West Virginia Maryland
Virginia District of
Columbia
• Population > 4.3 million
• Demand ~ 500 MGD
• 3 major suppliers – Washington Aqueduct
(a Division of the USACE)
– Washington Suburban Sanitary Commission (WSSC)
– Fairfax Water
Background
Washington Metropolitan Area
Water Supply System
Potomac intakes
Patuxent reservoirs (WSSC)
Occoquan Reservoir
(Fairfax Water)
Little Seneca
Reservoir Jennings Randolph Reservoir
Savage Reservoir
100 mgd flow-by
• 75% from Potomac River
• 25% from off-Potomac reservoirs
• 3 upstream reservoirs to augment Potomac flow
Background
2010 Reliability Study
Findings of Part 1 – Demand and Resource Availability for the year 2040 (based on historical climate) • The current system will likely meet demands through 2030
• By 2040 the current system may have difficulty meeting demands in event of severe drought
• Summertime outdoor water use may be increasing
Objective of Part 2: Determine potential impacts of climate change, assuming no management changes.
18 Climate Scenarios
3 Emission Scenarios
6 Global Models
Background
Historical Potomac Low Flow Periods
• Most severe droughts were 1930, 1966, 1999, and 2002
• This study’s primary focus is on a “moderate” drought, with likelihood comparable with drought of 1999
1930 drought of
record
1966 lowest documented
flow
1999 first water supply releases from Jennings
Randolph & Little Seneca
2002 drought plus
releases
2010 drought plus
releases
Approach
Overview
18 reliability forecasts for a
“moderate drought” assuming no management
changes
2040 climate: 18 global model projections
2040 weather: based on 1988-1999 data
PRRISM water supply model
Phase 5 Watershed
model
18 Potomac basin stream flow forecasts
Approach
Forecasting Daily Water Demands
• Daily demand forecasts are responsive to temperatures and precipitation changes
• Low reservoir levels trigger water use restrictions, and cause demand forecasts to drop
400
450
500
550
600
650
700
750
800
850
1-Jan 1-Feb 1-Mar 1-Apr 1-May 1-Jun 1-Jul 1-Aug 1-Sep 1-Oct 1-Nov 1-Dec
De
ma
nd
, mil
lio
n g
all
on
s p
er
da
y
Range of total area demand (restricted) under climate changeBaseline - no climate change
Dem
and
, mill
ion
gal
lon
s p
er d
ay
Baseline – no climate change Range of total demand under climate change
Results
Basin-wide Area Weighted Annual Water Budget
Results
Potomac Flows Decrease
0
10000
20000
30000
40000
50000
60000
1-Jan 1-Feb 1-Mar 1-Apr 1-May 1-Jun 1-Jul 1-Aug 1-Sep 1-Oct 1-Nov 1-Dec
Flo
w, m
illio
n g
allo
ns
pe
r d
ay
Range of predicted Potomac River flows under climate changeBaseline - no climate change
0
1000
2000
1-Jun 1-Jul 1-Aug 1-Sep
Closeup of summer drought flows
Results
Average Basin-wide Monthly Baseflow
Results
Water Use Restrictions Increase
Results
System Reliability
Shortfall definition: demands that must be met or reduced by new changes to the current system management
Results
Minimum Reservoir Storage
Conclusion Study Summary
Uncertainties/Limitations
• Range of projections from global models
• Less confidence in regional predictions
• Variability based on short time period (1988-1999)
• Uncertainty added by watershed modeling
2040 Water Supply Reliability (moderate drought conditions)
• Best scenarios: little impact
• Medium-impact scenarios: mandatory water use restrictions likely
• Worst-case scenarios: significant management/system changes required
Conclusion Potential Management/System Changes
To be evaluated in the 2015 reliability study:
• More operational efficiency
• Increased system flexibility
• Earlier and increased water use restrictions
• Additional water supply storage
Questions?
Contact • Sarah Ahmed, [email protected] • Cherie Schultz, PhD, [email protected] Acknowledgements • Cherie Schultz, Karin Bencala and Ross Mandel, Interstate
Commission on the Potomac River Basin, Rockville, Maryland • Lauren Hay, USGS National Research Program, Central Region,
Denver, Colorado • Mark Bennett, USGS Virginia Water Science Center,
Richmond, Virginia • Gary Shenk and Jing Wu, Chesapeake Bay Program Office,
Annapolis, Maryland