Alan F. Hamlet Dennis P. Lettenmaier Amy K. Snover JISAO Center for Science in the Earth System Climate Impacts Group and Department of Civil and Environmental Engineering University of Washington April, 2003 Climate Change Streamflow Scenarios for Critical Period Water Planning Studies

Changing Awareness of Climate Change in the Water Management Community ~1985: Global warming? ~1995: Is global warming real? ~1997: What are the expected impacts of climate change for our region and our water system? ~2002: How do we include climate change and climate uncertainty in long term planning to reduce risks?

Current Climate 2020s2040s The primary impact pathway in the western US: less snow Snow Water Equivalent (mm)

Columbia River at The Dalles for “Middle-of-the-Road” Scenarios

Effects to Moderate Elevation Basins in the Cascades

Project Motivation: Target existing planning processes at the watershed scale Make streamflow scenarios freely available to help reduce costs of including climate uncertainty in long-term planning (Recommendations from regional stakeholders and policy makers attending a CIG sponsored climate change workshop Skamania, 2001)

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

Project Goals: Create climate change streamflow scenarios that cover the same period of record and are numerically consistent with the historic record of streamflows traditionally used in water planning studies. Make these streamflow scenarios freely available on the web for a large number of river locations to facilitate the incorporation of climate change information into existing water planning efforts.

Choice of GCM Downscaling Methods for the Pilot Study Although more sophisticated methods are also available, the “Delta” method of downscaling GCM results was chosen for the pilot applications. Good fit with producing alternate versions of the historic record used in critical period planning studies. Easy to understand and interpret (the project has an educational component). Captures much of the regional scale information from GCM simulations.

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

Issues with Hydrologic Model Bias

Quantile-Based Bias Correction (Wood et al. 2002) VIC Input = Bias Corrected Output = 10000

Bias Correction Objectives: Result: Bias corrected hydrologic simulations are quite consistent with observed streamflows in absolute value and climate change signals are translated without significant distortion. Raw Bias Corrected

Bias Corrected Time Series Plot for the Current Climate

Bias Corrected Time Series Plot for the Composite 2040 Scenario

Web-Based Data Archive

Goals and Objectives of Two Regional-Scale Pilot Studies in the Pacific Northwest Northwest Power Planning Council: Primarily focused on reliability of the Columbia River hydropower system. Study will use the GENESYS model. Preliminary results in John Fazio’s talk this afternoon. Idaho Department of Water Resources: Primarily focused on groundwater/surface water interactions, sustainability of irrigated agriculture in the Snake River basin, groundwater/surface water interactions and water allocation amongst different users and uses.

Current Streamflow Routing Locations

Some Selected Results for the Snake River Basin (Composite Scenarios)

Planned Project Extensions Extend the period of record of the data to Extend the number of climate change scenarios and the downscaling methods used.

Summary and Conclusions Water policy workshops (Skamania 2001) have highlighted the need to inject climate change information into existing river basin planning activities where possible and to provide access to free streamflow scenarios to help reduce costs. Because most planning studies currently use a critical period framework, our project produces “adjusted” realizations of the historic streamflow record based on simulations from a physically based hydrologic model driven by simple climate change scenarios. The methods are flexible and portable and can be used to create streamflow scenarios deriving from different climate model scenarios, different downscaling methods, or different hydrologic models.