21st Century Water Management: The Myth of Climate Stationarity and Strategies for Water Resources Management in a Rapidly Evolving Climate Alan F. Hamlet •JISAO/CSES Climate Impacts Group •Dept. of Civil and Environmental Engineering University of Washington Climatological Foundation of U.S. Water Resources Planning and Management: 1) Risks are stationary in time. 2) Observed streamflow records are the best estimate of future variability. 3) Systems and operational paradigms that are robust to past variability are robust to future variability. Schematic of a Typical Water Planning Framework Observed Streamflows Planning Models System Drivers Annual streamflow reconstructions at The Dalles, OR using tree ring growth indices derived from douglas-fir and limber pine from SE British Columbia - Kamloops to Banff/Jasper (1750-1964) 350000 Columbia Basin Planning Window 300000 Observed Annual Streamflow Observed 5 yr mean 200000 Reconstructed Annual Streamflow Linear (Reconstructed Annual Streamflow) 150000 100000 y = -22.831x + 214682 50000 1975 1950 1925 1900 1875 1850 1825 1800 1775 0 1750 Flow (cfs) 250000 Trends in Annual Streamflow at The Dalles from 1858-1998 are strongly downward. 350000 250000 Annual 200000 5 yr mean 10 yr mean 150000 Linear (Annual) 100000 50000 0 1858 1868 1878 1888 1898 1908 1918 1928 1938 1948 1958 1968 1978 1988 1998 Annual Mean Flow (cfs) 300000 16.4 MAF was considered a conservative estimate at the time of the Compact. However, the average annual flow over the 20th century has been only 15 MAF. Relative to the gage record today, flows in the early 20th century appear to be unusually high. How unusual is this period in a longer-term context? (Figure Courtesy Connie Woodhouse) Tree rings placed the gage record in a long-term context Colorado River flow, reconstructed by Stockton and Jacoby, 1976 Stockton and Jacoby 1976 “…the timing of the drafting of the Compact was an unfortunate event, in that it did not occur during a representative flow period.” “The general picture of a collision between water demand and supply in the UCRB in the not-toodistant future is all too apparent.” Stockton and Jacoby 1976 (Figure Courtesy Connie Woodhouse) The Myth of Stationarity Meets the Death of Stationarity Muir Glacier in Alaska Aug, 13, 1941 Aug, 31, 2004 Image Credit: National Snow and Ice Data Center, W. O. Field, B. F. Molnia http://nsidc.org/data/glacier_photo/special_high_res.html Simulated Changes in Natural Runoff Timing in the Naches River Basin Associated with 2 C Warming 120 Simulated Basin Avg Runoff (mm) 100 80 Impacts: •Increased winter flow •Earlier and reduced peak flows •Reduced summer flow volume •Reduced late summer low flow 1950 60 plus2c 40 20 0 oct nov dec jan feb mar apr may jun jul aug sep 2000 1996 1992 1988 1984 1980 1976 1972 1968 1964 1960 1956 1952 1948 1944 1940 CRB 1936 CA 1932 1928 3 1924 1920 1916 Std Anomalies Relative to 1961-1990 Regionally Averaged Cool Season Precipitation Anomalies 4 PNW PRECIP GB 2 1 0 -1 -2 -3 Changes in Simulated April 1 Snowpack for the Canadian and U.S. portions of the Columbia River basin (% change relative to current climate) 20th Century Climate “2040s” (+1.7 C) -3.6% -21.4% April 1 SWE (mm) “2060s” (+ 2.25 C) -11.5% -34.8% Rebalancing Water Systems in Response to Climate Change Some Conflicting Objectives Likely to be Impacted by Climate Change: •Hydropower and water supply vs. flood control •Hydropower and water supply vs. instream flow and ecosystem services. •Interstate and international transboundary agreements 8000 7000 6000 5000 4000 3000 2000 1000 0 Sep Full 25000 20000 15000 : Current Climate Sep Aug Jul Jun May Apr Mar Feb Jan Dec Nov 10000 Oct Storage Jul Aug Jun Apr May Mar Feb Jan Dec Oct 30000 Nov Reservoir Inflow Flood Control vs. Refill Flood Control vs. Refill Streamflow timing shifts can reduce the reliability of reservoir refill 8000 + 2.25 oC 6000 5000 4000 3000 30000 Full 2000 1000 25000 20000 15000 : Current Climate Sep Aug Jul Jun May Apr Mar Feb Jan Dec 10000 Nov : + 2.25 oC No adaptation Oct Storage Sep Jul Aug Jun Apr May Mar Jan Feb Dec Oct 0 Nov Reservoir Inflow 7000 Flood Control vs. Refill Streamflow timing shifts can reduce the reliability of reservoir refill 8000 7000 + 2.25 oC 5000 4000 30000 3000 Full 2000 1000 : Current Climate Storage Aug 25000 Sep Jul Jun Apr May Mar Jan Feb Dec Oct 0 Nov 20000 : + 2.25 oC No adaption 15000 Sep Aug Jul Jun May Apr Mar Feb Jan Dec 10000 Nov : + 2.25 oC plus adaption Oct Reservoir Inflow 6000 Major U.S. Flood Control Checkpoints Bonners Ferry Columbia Falls The Dalles Optimization Reduces Storage Deficits without Jeopardizing Flood Protection 2,000 Storage Deficits 1,500 optimized 1,000 500 Duncan Libby Mica Hungry Horse Dworshak Climate change/no adaptation 600 Flood Risks Flow at The Dalles (kcfs) Grand Coulee 0 Arrow July 31 Average Storage Deficit (KAF) Climate change/no adaptation 500 400 300 optimized 200 100 -2 -1 0 1 2 3 Extreme Value Type I Distribution Reduced Variate, Y 4 5 Adaptation Strategies Approaches to Adaptation and Planning •Anticipate changes. Accept that the future climate will be substantially different than the past. •Use scenario based planning to evaluate options rather than the historic record. •Expect surprises and plan for flexibility and robustness in the face of uncertain changes rather than counting on one approach. •Plan for the long haul. Where possible, make adaptive responses and agreements “self tending” to avoid repetitive costs of intervention as impacts increase over time. Schematic of Climate Change Water Planning Framework Observed Streamflows Planning Models Altered Streamflows Climate Change Scenarios System Drivers Example of a Self-Tending Reservoir Operating System •Improved Streamflow Forecasts Incorporating Warming and Other Features of Altered Climate System •Dynamic Reservoir Operating Systems Using Optimization or Hybrid Optimization/Simulation Approaches to Rebalance the System. •Such systems are more flexible because they do not require a “trigger” for a change in the operating policies, and arguably do not require as much intervention as the climate system gradually changes, because the system responds autonomously to improvements in forecasts. •These ideas are not really new: Harvard Water Program ~1965 Cool Season Climate of the Western U.S. PNW GB CA CRB DJF Temp (°C) NDJFM Precip (mm) Global Climate Change Scenarios and Hydrologic Impacts for the PNW Observed 20th century variability °C +3.2°C +1.7°C +0.7°C 0.9-2.4°C 0.4-1.0°C Pacific Northwest 1.2-5.5°C Observed 20th century variability % -1 to +3% +1% +6% +2% -1 to +9% Pacific Northwest -2 to +21% Will Global Warming be “Warm and Wet” or “Warm and Dry”? Answer: 450000 Probably BOTH! Natural Flow Columbia River at The Dalles 350000 300000 250000 200000 2000 1990 1980 1970 1960 1950 1940 1930 1920 1910 150000 1900 Apr-Sept Flow (cfs) 400000 Schematic of VIC Hydrologic Model and Energy Balance Snow Model Snow Model The warmer locations are most sensitive to warming 2060s +2.3C, +6.8% winter precip Trends in April 1 SWE 1950-1997 Mote P.W.,Hamlet A.F., Clark M.P., Lettenmaier D.P., 2005, Declining mountain snowpack in western North America, BAMS, 86 (1): 39-49 DJF avg T (C) Overall Trends in April 1 SWE from 1947-2003 Trend %/yr Trend %/yr DJF avg T (C) Temperature Related Trends in April 1 SWE from 1947-2003 Trend %/yr Trend %/yr DJF avg T (C) Precipitation Related Trends in April 1 SWE from 1947-2003 Trend %/yr Trend %/yr 250 Simulated Basin Avg Runoff (mm) Chehalis River 200 150 1950 plus2c 100 50 0 oct nov dec jan feb mar apr may jun jul aug sep 500 Hoh River Simulated Basin Avg Runoff (mm) 450 400 350 300 1950 250 plus2c 200 150 100 50 0 oct nov dec jan feb mar apr may jun jul aug sep 200 Nooksack River Simulated Basin Avg Runoff (mm) 180 160 140 120 1950 100 plus2c 80 60 40 20 0 oct nov dec jan feb mar apr may jun jul aug sep Mapping of Sensitive Areas in the PNW by Fraction of Precipitation Stored as Peak Snowpack HUC 4 Scale Watersheds in the PNW Climate Change Impacts are Similar to Impacts of Water Management in PNW Hydropower Systems 30000 Estimated natural flows Streamflow (cfs) 25000 20000 nat 15000 obs 10000 5000 Skagit River at Mt. Vernon 0 10 11 12 1 2 3 4 5 6 7 8 9 Changes in Flood Risk in the Western U.S. Regionally Averaged Temperature Trends Over the Western U.S. 1916-2003 3.00 PNW Linear Trend (Deg. C per century) CA PNW 1.50 1.00 0.50 0.00 -0.50 -1.00 nov dec jan feb mar apr may jun jul aug sep 4.00 Linear Trend (Deg. C per century) CA CRB GBAS 2.00 oct GB CRB Tmax 2.50 CA 3.50 CRB Tmin GBAS 3.00 PNW 2.50 2.00 1.50 1.00 0.50 0.00 oct nov dec jan feb mar apr may jun jul aug sep DJF Avg Temp (C) Simulated Changes in the 20-year Flood Associated with 20th Century Warming DJF Avg Temp (C) X20 2003 / X20 1915 X20 2003 / X20 1915 X20 2003 / X20 1915 DJF Avg Temp (C) 20-year Flood for “1973-2003” Compared to “1916-2003” for a Constant Late 20th Century Temperature Regime X20 ’73-’03 / X20 ’16-’03 X20 ’73-’03 / X20 ’16-’03 Summary of Flooding Impacts Rain Dominant Basins: Possible increases in flooding due to increased precipitation variability, but no significant change from warming alone. Mixed Rain and Snow Basins Along the Coast: Strong increases due to warming and increased precipitation variability (both effects increase flood risk) Inland Snowmelt Dominant Basins: Relatively small overall changes because effects of warming (decreased risks) and increased precipitation variability (increased risks) are in the opposite directions. Landscape Scale Ecosystem Impacts Annual area (ha × 106) affected by MPB in BC 9.0 2005 Bark Beetle Outbreak in British Columbia 8.0 2004 7.0 6.0 5.0 2003 4.0 3.0 2.0 2002 1.0 2001 2000 1999 0 1910 1930 1950 1970 1990 2010 Year (Figure courtesy Allen Carroll) Temperature thresholds for coldwater fish in freshwater • Warming temperatures will increasingly stress coldwater fish in the warmest parts of our region – A monthly average temperature of 68ºF (20ºC) has been used as an upper limit for resident cold water fish habitat, and is known to stress Pacific salmon during periods of freshwater migration, spawning, and rearing +1.7 °C +2.3 °C Impact Pathways Associated with Climate •Changes in water quantity and timing Reductions in summer flow and water supply Increases in drought frequency and severity Changes in hydrologic extremes Changing flood risk (up or down) Summer low flows Changes in groundwater supplies •Changes in water quality Increasing water temperature Changes in sediment loading (up or down) Changes in nutrient loadings (up or down) •Changes in land cover via disturbance Forest fire Insects Disease Invasive species Impact Pathways Associated with Climate •Changes in water management practice Hydropower production (energy demand) Flood control operations (changing flood risk and refill statistics) Instream flow augmentation Use of storage to control water temperature •Changes in Ecosystem Protection and Recovery Planning Design of fish and wildlife recovery plans Habitat restoration efforts ESA listings (as a process) Monitoring programs Approaches to Adaptation and Planning •Anticipate changes. Accept that the future climate will be substantially different than the past. •Use scenario based planning to evaluate options rather than the historic record. •Expect surprises and plan for flexibility and robustness in the face of uncertain changes rather than counting on one approach. •Plan for the long haul. Where possible, make adaptive responses and agreements “self tending” to avoid repetitive costs of intervention as impacts increase over time.