Overview of New York City Water Supply Climate Change Research Don - - PowerPoint PPT Presentation

Overview of New York City Water Supply Climate Change Research

Don Pierson Section Chief Water Quality Modeling NYC DEP Bureau of Water Supply

New York City’s Water Supply System

§ New York City draws its drinking water from 1,972 square miles of watershed, extending to the Catskill Mountains, up to 125 miles north of the city. § 19 reservoirs and 3 aqueducts supply 1 billion gallons to more than 9.3 million people daily. § Catskill and Delaware watersheds currently supply 100 % of demand. § Croton watershed has potential to meet up to 30 % of demand.

Main Goals

v Identify the potential impacts of climate change using a quantitative modeling frame work.

v Interested in both Water Quantity and Quality v Consequences are difficult to predict as a result of complex interactions between processes

v Begin to evaluate paths to adaptation.

v WRF project 4262. Vulnerability assessment and risk management tools for climate change: Assessing potential impacts and identifying adaptation options v WRF Project 4306. Analysis of reservoir operations under climate change

Issues of Concern

Water Availability

§ Our region currently experiences intermittent drought and flooding

200 300 400 500 600 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 Billions of gallons

Cannonsville Reservoir, November 2001

Historic usable storage

N

Drinking Water Quality - Turbidity

§ Increased precipitation may cause increased turbidity in the Catskill system.

Catskill aqueduct intake

N

Drinking Water Quality - Eutrophication

• Changes in climate may affect trophic status

and phytoplankton.

• Changes in water temperature , thermal

structure and mixing, and the timing of nutrient delivery

Assessment and Action Plan, Report 1

1. Work with Climate Scientists to Improve Regional Climate Change Projections 2. Quantify Potential Climate Change Impacts

• n NYC Water Systems

3. Determine and Implement Appropriate Adjustments to NYC’s Water Systems 4. Inventory and Reduce Greenhouse Gas Emissions 5. Improve Communication and Tracking Mechanisms

DEP Climate Change Program Objectives

Climate Change Integrated Model Project

• Purpose : Evaluate the affects of climate change on NYC water supply
• Water storage and system operation
• Turbidity
• Nutrient loading and Eutrophication
• Project grew out of discussions in NYCDEP Climate Change Task

Force – Component of Climate Change Action Plan

• Major Project Tasks
• Develop credible future climate scenarios that can be used to drive watershed and reservoir

models

• Develop watershed hydrology, biogeochemical, erosion and sediment transport models that

adequately account for climate mediated processes

• Develop models of reservoir sediment transport and phytoplankton production that

adequately account for climate mediated processes

• Develop competence in forest modeling
• Apply models and data sets to make future predictions of the state on NYC water supply
• Collaboration
• CUNY Hunter College
• Allan Frei PI –
• 7 Post Docs hired – based at NYCDEP Kingston Offices
• Post Doc Advisors
• Tammo Steenhuis Cornell University
• Larry Band University of North Carolina

Turbidity

• Freq / Magnitude
• Alum Decisions

Watershed Models

(GWLF-VSA, SWAT)

Models

Flows WQ Loads

Integrated Modeling System

Watershed

• Land Use
• Soils
• Topography
• Hydrography
• GIS Based
• Management

Data Time Series

• Meteorology
• Flows
• WQ

Reservoir Models

(1D Hydrothermal Eutrophication, CEQUAL-W2) Reservoir WQ

Reservoir

• Bathymetry
• Infrastructure

System Model

(OASIS) Flows Operations

Results Watershed Management Land Use Changes Changes Trophic State Climate Change

(Delta Change, SDM,RCM)

Climate Change Analysis – Phase I

Flows

System

• Operating Rules
• Demand

System Performance

• Storage
• Demand
• Spills

Scales of Concern

v West of Hudson Water Supply 3500 km2 v Individual WOH reservoir watersheds 1180 km2-245 km2 v Watershed hydrologic simulations for reservoir system supply and operation ~ 1000 km2-4000 km2 v Watershed nutrient loading simulations ~100 km2 - 2000 km2 v Watershed turbidity loading simulations ~10 km2-100 km2 v Reservoir model simulations ~ 1km2 -50 km2

Results of CCIMP

Climate Data analysis

• Daily data sets obtained for 20 models 20c3m SRES A1B, A2, B1

scenarios 1960-2000, 2046-2065, 2081-2100

• Data have been interpolated to a common grid
• Common file format developed.
• Initial delta change (monthly factors) downscaling completed
• New frequency distribution downscaling method developed, that we

think better simulates change in events of different size

• Anandhi et al. Examination of change factor methodologies for climate change

impact assessment Accepted Water Resources Research

• GCM data evaluation/ranking of 20C3M scenarios – submitted to

BAMS

• Alternative methods for estimating future climate scenarios will be

evaluated

• Weather generators
• Dynamic downscaling methods
• Other statistical methods?

Development of Change Factor Methodology

Two Different Methods of Calculating Precipitation Change Factors Monthly Average Monthly Frequency Distribution

Results of Different CF Methods

J F M A M J J A S O N D 10 15 20 25 30 35 40

SRES A2, 2081-2100, Max. Precipitation (mm)

J F M A M J J A S O N D 5 10 15

1 bin 25 bin Obs

SRES A2, 2081-2100, 90th percentile Precipitation (mm)

Cannonsville Watershed Precipitation for 20 year Scenarios

Monthly Max Monthly 90th Percentile

Results of Different CF Methods

Cannonsville Watershed Mean Daily Air Temperature 20 year Scenarios

Monthly Max Monthly 90th Percentile

J F M A M J J A S O N D 5 10 15 20 25 30 35 40

SRES A2, 2081-2100, Max.

• Av. Temperature (
• C)

J F M A M J J A S O N D

• 5

5 10 15 20 25 30 35

SRES A2, 2081-2100, 90th percentile

• Av. Temperature (
• C)

Watershed Hydrology

• There is an important shift in the timing of streamflow
• Future increases in air temperature and precipitation

lead to:

• Increased evaporation and streamflow
• Decreased snow pack and snowmelt
• Increased snowmelt rain and stream flow in winter
• Decreased spring streamflow – due to lower snowmelt

0.1 0.2 0.3 0.4 0.5 0.6 J F M A M J J A S O N D

• 10
• 5

5 10 15 20 25 J F M A M J J A S O N D 1 2 3 4 5 6 7 8 J F M A M J J A S O N D

min max median 87.5 %tile 12.5 %tile

Watershed Model Results – 2081-2100 Scenarios Mean Daily Values

Air Temperature ( C) Total Precipitation (cm) Snowpack Water Equivalent (cm)

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 J F M A M J J A S O N D

Stream Discharge (cm)

Consequences of Changing Hydrology

• Greater winter streamflows lead to:
• Reservoirs filling earlier in Spring
• Greater release and spill in winter and spring

(including nutrients)

• Most climate scenarios suggest there will be

decreases in drought conditions

• Changes in the timing of nutrient and turbidity

inputs to reservoir

• Isothermal, cold lower ambient light

Future Challenges

• How will the frequency and intensity of extreme events change in the

future (e.g. mesoscale systems that cause turbidity in the reservoirs) ? How do we downscale GCM data to represent changes in the extremes?

• Model evaluation for climate sensitivity
• What model processes are most sensitive to Climate Change?
• Are these processes adequately represented in models?
• How do we deal with the large number of derived future climate

scenarios?

• How do we deal with uncertainty? Deterministic vs. Probabalistic?
• Extreme Events
• Stream and reservoir turbidity levels
• How do we separate effects of future changes in landuse from climate

change?

Questions?