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 Cannonsville Reservoir, November 2001 Historic usable storage 600 Billions of gallons 500 400 300 200 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010
Drinking Water Quality - Turbidity § Increased precipitation may cause increased turbidity in the Catskill system. N 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
DEP Climate Change Program Objectives Assessment and Action Plan, Report 1 1. Work with Climate Scientists to Improve Regional Climate Change Projections 2. Quantify Potential Climate Change Impacts on 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
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
Integrated Modeling System Climate Change Analysis – Phase I Data Models Results Changes Watershed Watershed Watershed - Land Use Management Models - Soils (GWLF-VSA, - Topography SWAT) - Hydrography Land Use - GIS Based Flows Flows Changes - Management WQ Loads Trophic Reservoir Climate Time Series State Models Change - Meteorology (1D Hydrothermal - Flows (Delta Change, Turbidity Eutrophication, - WQ SDM,RCM) -Freq / Magnitude CEQUAL-W2) -Alum Decisions Reservoir Flows Reservoir - Bathymetry Operations WQ - Infrastructure System System Performance System Model - Storage - Operating Rules - Demand (OASIS) - Demand - Spills
Scales of Concern v West of Hudson Water Supply 3500 km 2 v Individual WOH reservoir watersheds 1180 km 2 -245 km 2 v Watershed hydrologic simulations for reservoir system supply and operation ~ 1000 km 2 -4000 km 2 v Watershed nutrient loading simulations ~100 km 2 - 2000 km 2 v Watershed turbidity loading simulations ~10 km 2 -100 km 2 v Reservoir model simulations ~ 1km 2 -50 km 2
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 Cannonsville Watershed Precipitation for 20 year Scenarios Monthly 90 th Percentile Monthly Max SRES A2, 2081-2100, 90th percentile SRES A2, 2081-2100, Max. 40 1 bin 25 bin Obs 35 15 Precipitation (mm) Precipitation (mm) 30 25 10 20 15 10 5 J F M A M J J A S O N D J F M A M J J A S O N D
Results of Different CF Methods Cannonsville Watershed Mean Daily Air Temperature 20 year Scenarios Monthly 90 th Percentile Monthly Max SRES A2, 2081-2100, Max. SRES A2, 2081-2100, 90th percentile 40 35 35 30 o C) o C) 30 25 Av. Temperature ( Av. Temperature ( 25 20 20 15 15 10 10 5 5 0 0 -5 J F M A M J J A S O N D J F M A M J J A S O N D
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
Watershed Model Results – 2081-2100 Scenarios Mean Daily Values Air Temperature ( C) Total Precipitation (cm) 25 0.6 20 0.5 15 0.4 10 0.3 5 0.2 0 0.1 J F M A M J J A S O N D -5 0 -10 J F M A M J J A S O N D Snowpack Water Equivalent (cm) Stream Discharge (cm) 0.45 8 0.4 7 0.35 6 0.3 5 0.25 4 0.2 3 0.15 max 2 0.1 87.5 %tile 1 0.05 median 0 0 12.5 %tile J F M A M J J A S O N D J F M A M J J A S O N D min
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?
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