Potential Effects of Climate Change on New York City Water Supply Quantity and Quality: An Integrated Modeling Approach

Donald Pierson, Elliot Schneiderman and Mark Zion New York City Dept of Environmental Protection

Hampus Markensten and Emmet OwensUpstate Freshwater Institute

1. Project Overview

NYC DEP Climate Change Integrated Modeling Project

• Purpose: To evaluate the potential effects of future climate change on New York City Water Supply– Water availability and reservoir operations.– Reservoir eutrophication– Reservoir turbidity

• Multi-year project carried out in two phases. Now in early phase I

• This presentation will present initial Phase I modeling results.

• We are describing our methods and early progress – not final results

Original System Modeling Schematic

HistoricalClimate

WatershedModel

ReservoirModels

OASISModel

Integrated Model

SystemIndicators

HistoricalOperations

HistoricalRiver Flows

Early Phase I Model Connections

GCM/Delta ChangePredictions

WatershedModel

ReservoirModels

OASISModel

Integrated Model

SystemIndicators

AdjustedOperations

Turbidity Simulations Schoharie Reservoir

Eutrophication Simulations Cannonsville Reservoir

Phase I Climate Change Simulations

System Modeling of Reservoir Operations – All West of Hudson Reservoirs

2. Climate Change Projections

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

Control Period (1981-2000) 2.9 3.3 4.8 4.8 4.7 4.6 3.5 3.5 3.2 3.5 3.1 3.3

Future Period (2046-2065) 4.8 4.6 4.6 4.9 4.2 4.6 4.1 3.1 3.5 3.8 4.1 4.9

Delta Precip Factor = Future/Control 1.7 1.4 0.9 1.0 0.9 1.0 1.2 0.9 1.1 1.1 1.3 1.5

Average GCM-Projected Precipitation by Month for Control and Future Periods

Daily Precipitation Input Data for Model Simulations

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Application of Climate Change Delta Method - Precipitation

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Future +65yr

(Future = Baseline * Factor)

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Daily Air Temperature Input Data for Model Simulations

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Baseline

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Application of Climate Change Delta Method – Air Temp

Average GCM-Projected Air Temperature by Month for Control and Future Periods

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

Control Period (1981-2000) -5.4 -3.3 2.4 7.5 12.2 17.7 20.3 19.2 15.0 9.6 2.2 -2.5

Future Period (2046-2065) -1.6 -0.2 4.0 9.3 15.4 20.0 22.8 21.9 18.6 11.4 4.9 0.2

Delta Precip Factor = Future/Control 3.8 3.1 1.6 1.8 3.3 2.3 2.5 2.8 3.6 1.8 2.8 2.6

(Future = Baseline + Factor)

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Monthly Precipitation and Air Temperature Delta Change Factors

65 years forward (2046-2065)

•Expected monthly change in Precipitation

Based on 8 GCM/Emission Scenarios. Upper and lower bars are max and min of these. Box is the range of the remaining 6 scenarios. Vertical bar is the median of all scenarios.

(multiplicative factor)

(degrees C additive factor)

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•Expected monthly change in Air Temperature

100 years forward (2081-2100)

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3. Watershed Effects

GWLF Hydrologic Water Balance ModelPrecipitation

Snowpack

Mean Daily AirTemperature

Rain +Snowmelt

PET

ET

Runoff

Infiltration

UnsaturatedZone

Saturated Zone Baseflow

Streamflow

Latitude

RelativeHumidity

Solar Radiation

MeltCoeff

VegetationCover Coeff

CurveNumber Delay

Coeff

RecessCoeff

Soil WaterCapacity

UnsatLeakCoeff

Elevation

Season

Deep Seepage

SeepCoeff

GWLF Watershed Model ResultsSum of All WOH Watersheds

65 Yr Forward 100 Yr Forward

Temperature(oC)

Evapotranspiration(cm/day)

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Based on 8 GCM/Emission Scenarios. Upper and lower bars are max and min of these. Box is the range of the remaining 6 scenarios. Bar within box is the median. Line shows baseline run.

GWLF Watershed Model ResultsSum of All WOH Watersheds

65 Yr Forward 100 Yr Forward

Snow(cm/day)

Snowpack(cm)

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GWLF Watershed Model ResultsSum of All WOH Watersheds

65 Yr Forward 100 Yr Forward

Precipitation(cm/day)

Streamflow(cm/day)

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4. Water Supply System Effects

Effects of Climate Change on Reservoir Water Quantity using Delta Change, GWLF, and OASIS Models

GWLF Watershed

Models

OASIS Model

Historical Precip, AirTemp1966-2004

Climate Scenario Precip, AirTemp Stream

Flow

Reservoir Water Quantity

Simulate reservoir water balance.

Calculate reservoir operations based on current operating rules.

Delta Change

OASIS Model ResultsSum of All WOH Reservoirs

65 Yr Forward 100 Yr Forward

Reservoir Inflow(MGD)

Storage(BG)

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OASIS Model ResultsSum of All WOH Reservoirs

65 Yr Forward 100 Yr Forward

Release and Spill

(MGD)

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5. Turbidity Projections for Schoharie Reservoir

Effects of Climate Change on Turbidity in Schoharie Tunnel using Delta Change, GWLF, and W2 Models

GWLF Watershed

Model

Pre-Processor

W2 Reservoir

Model

Historical Precip, AirTemp

Climate Scenario Precip, AirTemp

Historical Tunnel Operation Data

StreamFlow

Net Flow In

Net turbidity In

Adj Tunnel Ops Data

Reservoir Water Quantity, Quality

Simulate reservoir water balance, and adjust tunnel data if withdrawal exceeds available storage.

Calculate turbidity inputs using sediment rating curve

Calculate net flow inputs

Reformat data for W2 model

Simulates water, temperature, and constituents in 2 dimensions (vertical, longitudinal)

Delta Change

Schoharie Reservoir Water Quantity Projections

65 yr forward

•Reservoir Storage (MG)

•Reservoir Spill (MG)

100 yr forward

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Schoharie Reservoir Turbidity Projections

65 yr forward

•Input Turbidity Load (ntu-mgd)

•Turbidity in Schoharie Tunnel (ntu)

100 yr forward

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6. Eutrophication Projections for Cannonsville Reservoir

Effects of Climate Change on Trophic Status of Cannonsville Reservoir using Delta Change, GWLF, and

PROTECH Models

GWLF Watershed

Model

Pre-Processor

PROTECHReservoir

Model

Historical Precip, Air Temp

Climate Scenario Precip, Air Temp

Historical Operation Data

Adj Ops Data

Reservoir Water Quantity, Quality

StreamFlow

Net Flow In

Nutrient Loads

Simulate reservoir water balance, and adjust tunnel data if withdrawal exceeds available storage.

Adjust Inflow water temperature

Adjust Air temp and dew point temp inputs to reservoir model

Calculate net flow inputs

Reformat data for PROTECH model

Simulates water, temperature, nutrients and phytoplankton functional groups in 1 dimension (vertical)

Delta Change

Adjusted Met Data

Adj Stream Temp

Nutrient Loads

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Dissolved Phosphorus (Kg/d)

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Water Surface Elevation (meters above sea level)

Particulate Phosphorus (Kg/d)

65 years forward 100 years forward

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Mean Reservoir Water Temperature (C)

Baseline

Delta Change based on ECAM A2 100 years forward

Water Temperature (C)

1994 1995 1996 1997

65 years forward 100 years forward

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Mean Reservoir Chlorophyll a (mg m-3)

Baseline

Delta Change based on ECAM A2 2081-2300

Chlorophyll a (mg m-3)

1994 1995 1996 1997

65 years forward 100 years forward

Why are these results preliminary?

1. Climate Change projections using delta change method don’t account for possible changes in storm frequency, intensity, and spatial variability.

2. Adaptation by adjustment of Reservoir Operations not accounted for.

3. Feedback between water quality and Reservoir Operations not accounted for

4. Effects of climate change on Ecosystem Processes not accounted for (Forest Health, Biogeochemical Cycles, Ecosystem Adaptation).

5. Effects of climate change on Channel Processes Affecting Turbidity not accounted for.

6. Model testing and sensitivity analysis needed to understand model predictions at extreme present climate and future climate conditions.

Summary• DEP’s Models were used with simple climate

scenarios (delta change) to obtain preliminary indication of the effects of climate change on water supply quantity and quality

• Initial results suggest– Reduced snowpack and spring melt– Greater fall and winter flows– Turbidity and nutrient loads follow flow pattern– Enhanced fall phytoplankton bloom

• Preliminary nature of these results are being addressed as the project progress.

EXTRA

Air

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GWLF Watershed Model ResultsSum of All WOH Watersheds

Annual Percent Change in Water Balance Components

65 Yr Forward 100 Yr Forward

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