Water Forward Overview April 24, 2019 1 Water Forward Integrated - PowerPoint PPT Presentation

Water Forward Overview April 24, 2019 1

Water Forward Integrated Water Resource Plan (IWRP) • Austin Water led interdepartmental effort to develop a 100 year water plan that reflects our community’s values • Council-appointed Task Force met monthly • Community outreach throughout the plan development process • Plan approved by Council in November 2018, with planned updates on a five year cycle • Goal: Ensure a diversified, sustainable, and resilient water future, with strong emphasis on water conservation 2

Austin’s Water Supply • Colorado River and Highland Lakes • Combination of state- granted water rights & long-term firm contract with Lower Colorado River Authority (325,000 acre-feet per year)

Historic 2008-2016 Drought Lake Travis, July 2011 and June 2016

Austin Municipal River Diversions

Austin Water Served Population

Water Forward Development ●Recommendation from 2014 Task Force ●Council Appointed Task Force convened in May 2015 ●Austin Water began work to develop scope and begin preliminary analysis ●By July 2016, consultant team procured included CDM Smith, Dr. Katherine Hayhoe (climate scientist), and Dr. Richard Hoffpauir (hydrologist)

Guiding Principles for Plan Development • Core Colorado River Supplies Protect • Public Health • Environment • Reliability • Conservation Focus On • Local Resources • Feasibility • Community Values Align With • Imagine Austin • Regional Coordination

Public Outreach Goals Map of over 90 public outreach events attended by Water Forward project team ●Identify community values to reflect in plan ●Seek input from stakeholders which reflect the diversity of Austin’s population ●Inform and educate the community throughout the process Neighborhood Association Meetings, Earth Day, Health Fairs, Interfaith Dialogue Meetings, Culture Town Halls, Imagine Austin Speaker Series

Alignment with Community Values Clean Safe Drinking Water Water Supply Conservation Reliability of Resources Cost and Environmental Affordability Stewardship

CLIMATE IMPACTS ON WATER SUPPLY AN AUSTIN CASE STUDY Marisa Flores-Gonzalez, Katharine Hayhoe, Richard Hoffpauir

MOTIVATION • Texas is already naturally at risk from regularly- occurring droughts and heavy rainfall events. • The risks we face are not static: they are rising • Every season in Texas has been warming since the 1950s • Warmer temperatures accelerate evaporation and increase water vapor in the atmosphere • This exacerbates the duration & severity of droughts and increases the frequency of heavy rainfall events 12

Example: Recent Drought Cumulative Inflows to Lakes Buchanan and Travis 1950's Drought vs Recent Drought 9 June 1957 8 122 months 7 Cumulative Inflow, Million acre-feet Apr. 1955 6 July 2018 96 months 130 months 5 Sep.1952 Pedernales Flood 65 months Jun. 2016 4 105 months Jun. 1951 3 50 months Apr. 2015 Feb. 2013 April 1949 91 months 65 months 2 24 months 1950s Cumulative Reference Inflow, Nov. 2011 1 May 1947 through June 1957 50 months Sep. 2009 2010's Cumulative Reference Inflow, 24 months October 2007 through July 2018 0 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 Months Since Start of Drought 13

Annual&Precipita.on&0&Quadrangle&710& 1600" 1400" 1200" 1000" 800" 600" 400" 200" "Model"Range" Obs" Linear"(Model"Trend)" 0" 1950" 1975" 2000" 2025" 2050" 2075" 2100" 14 Historical Texas precipitation and evaporation data available at: http://www.twdb.texas.gov/surfacewater/conditions/evaporation/index.asp

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Water Forward WAM Modeling Perform water availability simulations for 4 different future demand projection horizons with different hydrologic scenarios Observed Historical Future Climate Hydrology, Adjusted Hydrology No Adjustment Demand 77 Years of Projection 77 Years of Future Observed Results for Climate Adjusted Years Drought of Record Historical Hydrology, Hydrology 1940 – 2016 2020 X 2040 Stochastically Results for Stochastically 2070 Sampled Future Droughts Worse Sampled Observed than the Drought of Climate Adjusted 2115 Historical Hydrology Record Hydrology 16

STEP THREE STEP FOUR STEP ONE STEP TWO MODEL MODEL ANALYZE MODEL FUTURE FUTURE OBSERVATIONS OBSERVATIONS CLIMATE IMPACTS 17

HISTORICAL ANALYSIS • Use daily temperature and precipitation to calculate 120 indicators of average and extreme conditions over time scales ranging from 1 week to 24 months • Quantify and evaluate observed relationships between climate predictors and hydrologic parameters at the selected gauges 18

STREAMFLOW GAUGES Dallas # # ^ _ WEATHER STATIONS # # # # 1940-2016 # # # # # # # # # # # # # # # # # # # # # # # # # # Austin # ^ _ # # # # # # # Houston # _ ^ San Antonio ^ _ # # USGS Stream Gauges # E USGS Weather Stations _ ^ Cities Rivers 0 50 Miles Lakes and Bays 19

TOP STREAMFLOW PREDICTORS AVERAGE PRECIPITATION AVERAGE TEMPERATURE DRY DAYS EXTREME TEMPERATURE 20

COMPARING OBSERVED AND MODELED STREAMFLOW I10000 −− 1983 − 2013 0.8 OBSERVED MODELLED DOWNSCALED 0.6 MODELLED PAST PROBABILITY OBSERVED 0.4 0.2 0.0 Regarding Downscaling Technique, See Also -- 0 2 4 6 8 10 Stoner, A., Hayhoe, K., Yang, X., Wuebbles, D., 2012. An Asynchronous Regional Regression Model for Statistical 21 LOG(STREAMFLOW+1) Downscaling of Daily Climate Variables. International Journal of Climatology 33(11): 2473-2494.

GAUGE-SPECIFIC FUTURE PROJECTIONS OUR STREAMFLOW MODEL BASED ON HISTORICAL OBSERVATIONS 20 GLOBAL CLIMATE MODELS 22

Historical and Adjusted WAM Naturalized Flows for Austin’s IWRP 77 Years, 1940 - 2016 Colorado River at Austin Long-term mean flow is the same to Droughts are longer and drier. slightly lower depending on the group of High flows are higher. future conditions. Variability increases with future conditions. 23

Historical and Adjusted WAM Naturalized Flows for Austin’s IWRP 77 Years, 1940 - 2016 Colorado River at Winchell Long-term mean flow decreases with Droughts are longer and drier. future conditions. High flows are about the same or lower. Variability decreases with future conditions. 24

Beyond the 2010’s Drought for Austin’s IWRP • The period of record contains 2 major droughts. • For Austin’s Water Forward IWRP, consideration of droughts worse than the drought of record (DWDR’s) incorporated as prudent risk management for long- term planning. • Goal for DWDR Selection in Austin’s IWRP : Select candidate DWDR events that represent a variety of drought duration and severity combinations. Water supply reliability metrics developed for candidate droughts. 25

Markov Chain Monte Carlo Sampling High, Upper 1/3 Step #1 Classify each year in period of Step #3 Step #4 Medium, Middle 1/3 record based on annual Select Select Low, Lower 1/3 flow volumes sequence specific of states year 1940 1950 1960 1970 1980 1990 2000 2010 High 2007 1941 1951 1961 1971 1981 1991 2001 2011 Med 1985 1942 1952 1962 1972 1982 1992 2002 2012 Med 1966 1943 1953 1963 1973 1983 1993 2003 2013 Low 2012 1944 1954 1964 1974 1984 1994 2004 2014 Low 1947 1945 1955 1965 1975 1985 1995 2005 2015 Med 1995 1946 1956 1966 1976 1986 1996 2006 2016 Low 2006 1947 1957 1967 1977 1987 1997 2007 Low 1972 1948 1958 1968 1978 1988 1998 2008 Low 1993 1949 1959 1969 1979 1989 1999 2009 High 1957 High 1965 Step #2 Calculate transition probability between states Med 2000 based on the observed transitions Med 1994 Annual Transition State Low 2011 Low Med High Med 1978 Prior Low 42.3% 38.5% 19.2% High 1951 Annual Med 26.9% 26.9% 46.2% High 1989 State High 33.3% 33.3% 33.3% Step #5 Build extended WAM hydrology input files according to the 26 sequence of selected years

Drought Return Periods Assign probabilities to duration, severity, and joint probability of duration & • severity. Return period calculated for the occurrence of duration and severity both exceeding the levels shown. Recent Drought 1950s Drought Regarding steps from SPI/SRI to Drought Return Period, See Fig.2 in – Halwatura, D., Lechner, A., Arnold, S., 2015. Drought Severity-Duration-Frequency Curves: A 27 Regarding Drought Return Period, See Also -- Shiau, J. 2006. Fitting Drought Duration and Foundation for Risk Assessment and Planning Tools for Ecosystem Establishment in Post-Mining Landscapes. Hydrol. Earth Syst. Sci. 19(2): 1069-1091. Severity with Two-Dimensional Copulas. Water Resources Management, 20(5), 795-815.

28 Summary • Regular IWRP updates will address new information. • Historical hydrology is a key component of long-term planning, however for Austin’s IWRP it was also important to consider planning for change and uncertainties. • For Austin’s IWRP, prudent risk management for long-term planning considers: – potential changes to hydrology based on the best available science, and – drought scenarios that differ from and are worse than the past.