Decision Relevant Climate Change Impact Assessments using WEAP21

1. Decision Relevant Climate Change Impact Assessments using WEAP21 Stockholm Environment Institute-Boston Center National Center for Atmospheric Research Natural Heritage Institute with support from: U.S. EPA, Office of Research and Development

2. Let’s start with a quick introduction to the original version of WEAP, and most other water resource management simulation models for the matter.

3. A Simple System

4. What are we assuming? • That we know how much water is flowing at the top of each river. • That we know how much water is flowing into or out of the river as it moves downstream. • That we know what the water demands are with certainty.

5. What are we assuming? • That we know how much water is flowing at the top of each river. • That we know how much water is flowing into or out of the river as it moves downstream. • That we know what the water demands are with certainty. • Basicly, that this system has been removed from it HYDROLOGIC context.

6. What do we do now?

7. ADD HYDROLOGY!

8. Hydrology Model Critical question: How does rainfall on a catchment translate into flow in a river? Critical question: What pathways does water follow as it moves through a catchment? Runoff? Infiltration? ET? Seepage? Critical question: How does movement along these pathways impact the magnitude, timing, duration and frequency of river flows?

9. Planning Model Critical question: How should water be allocated to various uses in time of shortage? Critical question: How can these operations be constrained to protect the services provided by the river? Critical question: How should infrastructure in the system (e.g. dams, diversion works, etc) be operated to achieve maximum benefit? Critical question: How will allocation, operations and operating constraints change if new management strategies are introduced into the system?

10. WEAP, with its integrated Hydrology Molude, provides a framework for answering both set of questions.

11. WEAP Hydrology

12. The WEAP 2-Bucket Hydrology Module Surface Runoff = f(Pe,z1,1/LAI)

13. One 2-Bucket Model Per Land Class

14. This last point leads to a stylized groundwater representation

15. An Example from California

16. WEAP Schematic of Sacramento Watershed Based Model

17. Calibration and Validation • Model Evaluation (1961-1999): • Flows Along Mainstem and Tributaries • Reservoir Storage and Release • Trinity Diversion • Agricultural Water Demand • Groundwater Storage Trends • Yolo Bypass Flood Inundation • Sacramento River Water Temperature

18. Reservoir Storage SHASTA

19. Stylized Sacramento Climate Scenarios

20. Phenologies of reproductive events in freshwater phase of Chinook salmon life-cycle in the SV watershed.□ = adult immigration; ∆ = spawning and hatching; ◊ = juvenile emigration

21. River Temperature Model • First-order DO and temperature patterned after Chapra (1997) • Water quality simulated for select rivers, where tributaries, discharges, and return flows prescribed. • Mass balance equations for each stream segment • Hydrologic inflows from rivers and groundwater sources simulate the water balance and mixing of concentrations and temperature along each reach. • Same River network for the water resources and the water quality simulation, and assumes complete mixing.

22. Temp. Profile – Kms Downriver of Shasta Dam

23. Current Decision-Relevant Activity • Collaborating with PCWA and EID on the development of a WEAP21 model of the American River Watershed for exploration of potential climate change impacts. • Collaborating with DWR to see if the WEAP21 Framework can contribute to the “quantitative climate change assessment” envisioned for B160-2010. • Working with the California Climate Center on a case study for the Sacramento Valley as part of a climate change assessment report called for under Governor Schwarzenegger’s Executive Order S-3-05.

24. Approach • Develop refined WEAP model of the American River watershed. • Apply the model to understand hydropower potential of PCWA system. • Apply the model to understand the drought vulnerability of the EID water supply system. • Potentially integrated with a model of the Yuba River watershed which is managed by Nevada Irrigation District and has substantial transfers into the American River watershed.

25. The American River Watershed in WEAP21

26. North Fork American

27. Preliminary Calibration 1990 - 1999

28. Warmer and Drier Climate Scenario

29. Current Decision-Relevant Activity • Collaborating with PCWA and EID on the development of a WEAP21 model of the American River Watershed for exploration of potential climate change impacts. • Collaborating with DWR to see if the WEAP21 Framework can contribute to the “quantitative climate change assessment” envisioned for B160-2010. • Working with the California Climate Center on a case study for the Sacramento Valley as part of a climate change assessment report called for under Governor Schwarzenegger’s Executive Order S-3-05.

30. Approach • Train DWR staff on the use of WEAP. • Develop a link between Sacramento Valley application and a Delta Water Quality Model. • Develop a link with a future demand scenario generator developed by RAND. • Embed the Sacramento Valley application in a more stylized system-wide model. • Run a series of climate change scenarios. • Evaluate with DWR if the WEAP framework can be used for quantitative climate change analysis in Bulletin 160-2010.

31. Current Decision-Relevant Activity • Collaborating with PCWA and EID on the development of a WEAP21 model of the American River Watershed for exploration of potential climate change impacts. • Collaborating with DWR to see if the WEAP21 Framework can contribute to the “quantitative climate change assessment” envisioned for B160-2010. • Working with the California Climate Center on a case study for the Sacramento Valley as part of a climate change assessment report called for under Governor Schwarzenegger’s Executive Order S-3-05.

32. Approach • Disaggregate HUCs to ID level • Calibrate model • Run climate change scenarios • Modify assumptions (e.g. changing irrigation technology/efficiency, varying cropping patterns, conversion of farmland to urban use, etc.) • Re-run scenarios • Perform economic assessment

33. Spatial Disaggregation Sacramento Valley WEAP Model

34. Spatial Disaggregation Before After Stone Corral HUC

35. Model Calibrated for Stone Corral • Regional water consumption and delivery within Sacramento-Stone Corral HUC corresponds to historic data. • Irrigation district level water consumption and delivery reflects historic observations. • Groundwater levels follow historic trend.

36. Future Work • Disaggregate and calibrate Lower Butte HUC • Run climate change scenarios • Modify Assumptions (e.g. add dynamic cropping patterns) • Perform economic assessment

37. Conclusions • The hydrology module is a powerful tool for considering changing catchment dynamics. • Hydrology is essential for conducting rigorous analysis of climate change impacts. • Hydrology could be very interesting for sectoral economic analysis because it considers several resources in a catchment, rainfed and irrigated agriculture, forest and range management, fish appropriate flows. • Increasing activity is taking place with the WEAP21 Framework in California, with the real potential to influence decision-making processes.