Effects of Climate Change on Hydropower Resources in the PNW and Western U.S. JISAO Center for Science in the Earth System Climate Impacts Group and Department of Civil and Environmental Engineering University of Washington March, 2006 Alan F. Hamlet Philip W. Mote Nathan Mantua Dennis P. Lettenmaier

Example of a flawed water planning study: The Colorado River Compact of 1922 The Colorado River Compact of 1922 divided the use of waters of the Colorado River System between the Upper and Lower Colorado River Basin. It apportioned **in perpetuity** to the Upper and Lower Basin, respectively, the beneficial consumptive use of 7.5 million acre feet (maf) of water per annum. It also provided that the Upper Basin will not cause the flow of the river at Lee Ferry to be depleted below an aggregate of 7.5 maf for any period of ten consecutive years. The Mexican Treaty of 1944 allotted to Mexico a guaranteed annual quantity of 1.5 maf. **These amounts, when combined, exceed the river's long-term average annual flow**.       

What’s the Problem? Despite a general awareness of these issues in the water planning community, there is growing evidence that future climate variability will not look like the past and that current planning activities, which frequently use a limited observed streamflow record to represent climate variability, are in danger of repeating the same kind of mistakes made more than 80 years ago in forging the Colorado River Compact. Long-term planning and specific agreements influenced by this planning (such as the long-term licensing of hydropower projects and water permitting) should be informed by the best and most complete climate information available, but frequently they are not.

Greenhouse Gas Concentrations are Rising Rapidly Due to Human Activity

Natural AND human influences explain the observations of global warming best. Natural Climate Influence Human Climate Influence Red: observations of global average temperature Grey: simulations with a climate model (huge computer program, like weather prediction model only run for hundreds of years) Natural influence: volcanoes, solar variations – guesses before ~1970, better since then Human influence: greenhouse gases, sulfate aerosols it is possible to simulate the climate of the last 100 years, and the conclusion is that humans didn’t matter much before 1960 – the early warming and the cooling were largely natural, and the late-century warming was largely human-caused All Climate Influences

Temperature trends (°F per century) since 1920 cooler warmer 3.6°F 2.7°F 1.8°F 0.9°F Each dot represents a station with data going back at least to 1920, size of dot shows magnitude of linear trend. Open circles are negative trends - not many of those. Most trends in the 1-3F range. The regional average (using appropriate area-weighting) is 1.5F/century. These data have been quality-controlled and corrected by the National Climate Data Center. This includes removing the “urban warming” effect, which is statistically estimated.

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

spring flows rise and summer flows drop As the West warms, spring flows rise and summer flows drop Stewart IT, Cayan DR, Dettinger MD, 2005: Changes toward earlier streamflow timing across western North America, J. Climate, 18 (8): 1136-1155 Spring snowmelt timing has advanced by 10-40 days in most of the West, leading to increasing flow in March (blue circles) and decreasing flow in June (red circles), especially in the Pacific Northwest.

Observed 20th century variability Curves are fits to ln(CO2) for A2 (solid) and B1 (dashed) Warming ranges are shown for 2020s, 2040s and 2090s relative to 1990s. Central estimates: 0.7C by 2020s, 1.7C by 2040s, 3.2C by 2090s. Pink box shows +/- 2 sigma for annual average temperature (sigma=0.6C). Red lines show previous generation of change scenarios. Pacific Northwest

Observed 20th century variability % +6% +2% +1% Curves are fits to ln(CO2) for A2 (solid) and B1 (dashed) Precip changes are shown for 2020s, 2040s and 2090s relative to 1990s. Central estimates: 1% by 2020s, 3% by 2040s, 6% by 2090s. Pink bar shows +/- 2 sigma for PNW annual precip. Observed 20th century variability -1 to +3% -1 to +9% -2 to +21% Pacific Northwest

Hydroclimatology of the Pacific Northwest

Annual PNW Precipitation (mm) Columbia River Basin Useable Storage ~35 MAF ~50% of storage is in Canada ~Storage is 30% of annual flow Snowpack functions as a natural reservoir The Dalles Elevation (m)

Effects of the PDO and ENSO on Columbia River Summer Streamflows PDO Cool Cool Warm Warm high high low low Ocean Productivity

Warming Affects Streamflow Timing Temperature warms, precipitation unaltered: Streamflow timing is altered Annual volume may be somewhat lower due to increased ET Black: Obs Red: 2.3° C warming Using a hydrologic simulation model we can evaluate the effects of warming on streamflow in isolation. Precipitation is held constant and temperatures are raised by about 4.1 F. The primary effect is on streamflow timing. Winter flows increase, summer flows decline. This effect is primarily related to changes in snow accumulation and melt. Increased temperatures also result in decreases the annual flows, although these effects are relatively small for this amount of warming (see Slide 10).

Precipitation Affects Streamflow Volume Precipitation increases, temperature unaltered: Streamflow timing stays about the same Annual volume is altered Black -- Obs Blue -- 9% increase in precip. Using a hydrologic simulation model we can evaluate the effects of precipitation changes on streamflow in isolation. Temperature is held constant and precipitation is increased by about 9% in winter. The primary effect is on streamflow volume. Annual flows increase by about 10% percent.

Global Climate Change Scenarios and Hydrologic Impacts for the PNW

Four Delta Method Climate Change Scenarios for the PNW Somewhat wetter winters and perhaps somewhat dryer summers

Changes in Mean Temperature and Precipitation or Bias Corrected Output from GCMs ColSim Reservoir Model VIC Hydrology Model

The warmest locations are most sensitive to warming +4.5% winter precip

Changes in Simulated April 1 Snowpack for the Canadian and U. S Changes in Simulated April 1 Snowpack for the Canadian and U.S. portions of the Columbia River basin (% change relative to current climate) Current Climate “2020s” (+1.7 C) “2040s” (+ 2.25 C) -3.6% -11.5% -21.4% -34.8% April 1 SWE (mm)

Naturalized Flow for Historic and Global Warming Scenarios Compared to Effects of Regulation at 1990 Level Development Historic Naturalized Flow Estimated Range of Naturalized Flow With 2040’s Warming Regulated Flow

Decadal Climate Variability and Climate Change

Will Global Warming be “Warm and Wet” or “Warm and Dry”? Answer: Probably BOTH!

Water Resources Implications for the Columbia River Basin

Impacts on Columbia Basin hydropower supplies Winter and Spring: increased generation Summer: decreased generation Annual: total production will depend primarily on annual precipitation (+2C, +6%) (+2.3C, +5%) (+2.9C, -4%) NWPCC (2005)

Warming climate impacts on electricity demand Reductions in winter heating demand Small increases in summer air conditioning demand in the warmest parts of the region From a variety of charts in an NWPCC report (http://www.nwcouncil.org/library/2002/2002-11.pdf; see Fig.15), the monthly electricity demand during the winter is ~25000 MW; during the summer it's more like 20000 MW. So, the changes in winter demand in this figure are probably a reduction ~10% (as a maximum). This jives with some of the graphs from Sailor (I attached one) that calculates the sensitivity of electricity consumption for a 2 degree C warming to be a little less than 10%. NWPCC 2005

Adaptation to climate change will require complex tradeoffs between ecosystem protection and hydropower operations Source: Payne, J.T., A.W. Wood, A.F. Hamlet, R.N. Palmer, and D.P. Lettenmaier, 2004, Mitigating the effects of climate change on the water resources of the Columbia River basin, Climatic Change, Vol. 62, Issue 1-3, 233-256

Flood Control vs. Refill Streamflow timing shifts can reduce the reliability of reservoir refill Full Model experiments (see Payne et al. 2004) have shown that moving spring flood evacuation two weeks to one month earlier in the year helps mitigate reductions in refill reliability associated with streamflow timing shifts. Payne, J.T., A.W. Wood, A.F. Hamlet, R.N. Palmer, and D.P. Lettenmaier, 2004, Mitigating the effects of climate change on the water resources of the Columbia River basin, Climatic Change, Vol. 62, Issue 1-3, 233-256

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

Implications for Hydropower Licensing Agreements Because of the long time frame of hydropower licensing agreements, considerable changes in climate and streamflow are likely to occur during the life of the license. These changes will tend to “unbalance” existing tradeoffs between water resources objectives such as hydropower, flood control, water supply, instream flow, and water temperature. Different users and uses of water will not be impacted equally. As warming progresses, water management plans will need to be updated regularly to cope with what we believe will be rapidly evolving conditions. If current licensing agreements are not robust to these expected hydrologic changes and do not include flexible mechanisms for updating the agreements, law suits or other challenges to the license could occur as warming progresses. To cope with these issues, new tools and approaches are needed to create licensing agreements that can adapt autonomously to changing hydrologic conditions and “rebalance” tradeoffs between different uses in a well defined and agreed upon manner. Such approaches are technically feasible.

Selected References and URL’s Climate Impacts Group Website http://www.cses.washington.edu/cig/ White Papers, Agenda, Presentations for CIG 2001 Climate Change Workshop http://jisao.washington.edu/PNWimpacts/Workshops/Skamania2001/WP01_agenda.htm Climate Change Streamflow Scenarios for Water Planning Studies http://www.ce.washington.edu/~hamleaf/climate_change_streamflows/CR_cc.htm Northwest Power and Conservation Council Columbia Basin Hydropower Study http://www.nwppc.org/energy/powerplan/plan/Default.htm Refs on Climate Variability and Climate Change http://www.ce.washington.edu/~hamleaf/hamlet/publications.html

Observed Hydrologic Changes