Alan F. Hamlet Philip Mote Dennis P. Lettenmaier JISAO Center for Science in the Earth System Climate Impacts Group and Department of Civil and Environmental Engineering University of Washington October, 2003 Considering Climate Variability and Climate Change in Long-Term Water Planning

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**.

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) should be informed by the best and most complete climate information available, but frequently they are not. What’s the Problem?

Overview: What do we know about Pacific Northwest climate variability and river flow over the past 250 years or so? What should we expect for the 21st century? How can planners bring this information to bear on long- range water planning?

Hydroclimatology of the Pacific Northwest

Annual PNW Precipitation (mm) Elevation (m) The Dalles

Winter Precipitation Summer Precipitation (mm)

Hydrologic Characteristics of PNW Rivers

Temperature warms, precipitation unaltered: Streamflow timing is altered Annual volume stays about the same Precipitation increases, temperature unaltered: Streamflow timing stays about the same Annual volume is altered Sensitivity of Snowmelt and Transient Rivers to Changes in Temperature and Precipitation

A history of the PDO warm cool warm A history of ENSO Pacific Decadal OscillationEl Niño Southern Oscillation

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

Long-Term Trends in Temperature, Precipitation, and Streamflow

Area-weighted Regional Avg=1.5 F/century

Annual Precipitation Trends From HCN stations

Winter precipitation and annual flow in the Columbia River are highly correlated and are both gradually increasing since 1916 (Trend ~ +7% per century) (Comparison of Annual Flow at The Dalles and Predicted Flow Based on Oct-Mar Basin-Average Precipitation from )

Trends in Annual Streamflow at The Dalles from are strongly downward.

Source: Gedalof, Z., D.L. Peterson and Nathan J. Mantua. (in review). Columbia River Flow and Drought Since Submitted to Journal of the American Water Resources Association. The Dust Bowl was probably not the worst drought sequence in the past 250 years red = observed, blue = reconstructed

Global Climate Change Scenarios and Impacts on the PNW

Humans are altering atmospheric composition

The earth is warming -- abruptly

Natural Climate InfluenceHuman Climate Influence All Climate Influences Natural AND human influences explain the observations best.

Emissions scenarios we chose are “middle of the road” ones

1 BMRC 2 CCC 3 CCSR 4 CSIRO 5 ECHAM3 6 ECHAM4 7 GFDL 8 HadCM2 9 IAP 10 MRI 11 CERFACS 12 PCM 13 GISS 14 HadCM3 15 LMD 16 CSM Higher Predictive Skill For Temperature Lower Predictive Skill For Precipitation Climate models predict temperature more accurately than precipitation.

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

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

Current Climate 2020s2040s Snow Water Equivalent (mm) VIC Simulations of April 1 Average Snow Water Equivalent for Composite Scenarios (average of four GCM scenarios) The main impact: less snow

Reductions in Snowpack for PCM Scenarios (low sensitivity)

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

Effects to the Cedar River (Seattle Water Supply) for “Middle-of-the-Road” Scenarios

Frequency of Drought in the Columbia River Comparable to Water Year 1992 (data from ) x 2 x 4.7 x 1.3

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 (in press). Adaptation to climate change will require complex tradeoffs between ecosystem protection and hydropower operations

Monitoring Climate Change Impacts

20th century decline in NH snow cover R.D. Brown, J. Climate, 2000 Satellite meas. Surface measurements

Trends in April 1 snow water equivalent, Mote, P.W., 2003: Trends in snow water equivalent in the Pacific Northwest and their climatic causes. Geophysical Research Letters.

Snowmelt runoff timing trends, Graphic provided by Dan Cayan, Scripps Institute of Oceanography and the USGS. To appear in Climatic Change, 2003

Strategies and Tools for Incorporating Climate Information in Long-Term Water Planning

Broad Strategies for Incorporating Climate Variability and Climate Change in Long-Term Water Planning Identify and Assess Climate Linkages Identify potential linkages between climate and resource management that could affect outcomes in the long term. What’s being left out? Are there future “deal breakers” in these omissions? (e.g. ocean productivity, glaciers maintaining summer streamflow in the short term) Design for Robustness and Sustainability Use modeling studies to test preferred management alternatives for robustness in the face of climate variability represented by paleoclimatic studies, conventional observations, and future climate change projections. Identify Limits and Increase Response Capability Use estimates of uncertainties or “what if” scenarios to find the performance limits inherent in preferred management alternatives. How can response capability be increased? Expect Surprises and Design for Flexibility to Changing Conditions Design contingency planning into management guidelines to allow for ongoing adaptation to unexpected (or uncertain) conditions without recursive policy intervention.

Observed Streamflows Planning Models System Drivers Critical Period Planning Methods for Water Studies

Observed Streamflows Climate Change Scenarios Planning Models Long term planning for climate change may include a stronger emphasis on drought contingency planning, testing of preferred planning alternatives for robustness under various climate change scenarios, and increased flexibility and adaptation to climate and streamflow uncertainty. Altered Streamflows System Drivers Incorporating Climate Change in Critical Period Planning

Bias Corrected Time Series Plot for the Current Climate

Bias Corrected Time Series Plot for the Composite 2040 Scenario

Web-Based Data Archive

Conclusions: The integrated and cumulative impacts of climate variability and climate change on water resources need to be incorporated more effectively in long-term water planning if we are to avoid costly mistakes in forging long-term water and energy policies and in allocating water for future use. Including better information on climate variability and climate change in water planning will require some changes in the way we do things, but good tools and sources of information are available to assist with the process.