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Los Angeles Basin Stormwater Conservation Study

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Los Angeles Basin Stormwater Conservation Study Technical Memorandum No. 86-68210-2013-05 Los Angeles Basin Stormwater Conservation Study Task 3.1 Development of Climate-Adjusted Hydrologic Model Inputs U.S. Department of the Interior Technical Service Center Bureau of Reclamation October 2013 Mission Statements The mission of the Department of the Interior is to protect and provide access to our Nation’s natural and cultural heritage and honor our trust responsibilities to Indian Tribes and our commitments to island communities. The mission of the Bureau of Reclamation is to manage, develop, and protect water and related resources in an environmentally and economically sound manner in the interest of the American public. Cover Photo: Morris Dam across the San Gabriel River, California. Los Angeles Basin Stormwater Conservation Study Task 3.1. Development of Climate- Adjusted Hydrologic Model Inputs Prepared by: Water and Environmental Resources Division (86-68200) Water Resources Planning and Operations Support Group (86-68210) Flood Hydrology and Consequences Group (86-68250) Victoria Sankovich, Meteorologist Subhrendu Gangopadhyay, Hydrologic Engineer Tom Pruitt, Civil Engineer R. Jason Caldwell, Meteorologist Peer reviewed by: Ian Ferguson, Hydrologic Engineer Los Angeles Basin Study Task 3.1 Development of Climate-Adjusted Hydrologic Model Inputs Contents Page Executive Summary .................................................................................................... ES-1 1. Introduction ............................................................................................................. 1 1.1 Study Purpose and Objectives ................................................................................. 1 1.2 Description of LA Basin Study Area ......................................................................... 1 1.3 Potential Future Climate Change Impacts ................................................................ 2 1.3.1 Literature Review ............................................................................................. 2 1.3.2 LA Basin Study Task 3.1 ................................................................................. 4 2. Development of Climate-Adjusted Hydrologic Model Inputs ............................. 5 2.1 Historical Data .......................................................................................................... 5 2.1.1 Historical Precipitation Data ............................................................................ 5 2.1.2 Historical Potential Evaporation Data .............................................................. 6 2.2 Future Climate Projections ....................................................................................... 6 2.2.1 Global Climate Models (GCM)......................................................................... 6 2.2.2 Downscaled Projections .................................................................................. 8 2.3 Spatial and Temporal Subsets of Climate Projections ........................................... 10 2.3.1 Spatial Subsets .............................................................................................. 10 2.3.2 Temporal Subsets ......................................................................................... 11 2.4 CMIP3-BCSD and CMIP5-BCSD Climate Scenarios ............................................. 12 2.4.1 CMIP3-BCSD and CMIP5-BCSD Projection Selection ................................. 12 2.4.2 Hourly Precipitation Time-Series For CMIP3-BCSD and CMIP5-BCSD Projections ..................................................................................................... 16 2.4.3 Hourly Evaporation Time-Series Under CMIP3-BCSD and CMIP5-BCSD Projections ..................................................................................................... 20 2.5 CMIP5-BCCA Climate Projections .......................................................................... 21 2.5.1 CMIP5-BCCA Projection Selection ............................................................... 21 2.5.2 Hourly Precipitation Time-Series Under CMIP5-BCCA Projections .............. 22 2.6 Climate-Adjusted Hydrologic Inputs ........................................................................ 23 3. Storm Event Frequency For Future Climate Projections .................................. 27 3.1 Storm Event Frequency for the CMIP3-BCSD and CMIP5-BCSD Projections ...... 27 3.2 Storm Event Frequency for the CMIP5-BCCA Projections .................................... 28 3.3 Discussion of Storm Event Frequency Results ...................................................... 30 4. Summary and Conclusions .................................................................................. 35 4.1 Existing Projections ................................................................................................ 35 4.2 Climate Scenarios .................................................................................................. 36 4.3 Hourly Projections of Precipitation and Potential Evaporation ............................... 36 4.4 Storm Event Frequency .......................................................................................... 36 5. References .............................................................................................................. 39 i Los Angeles Basin Study Downscaled Climate Change Report List of Tables Table 1. Years and Duration Associated with the Simulated Historical Period ................ 12 Table 2. CMIP5-BCCA Projections Used in this Study (Reclamation 2013). ................... 22 Table 3. Historical and Projected Monthly Means of Potential Evaporation (in inches) for Evaporation Measurement Station 23129. ................................... 25 Table 4. Historical and Projected Monthly Means of Precipitation (in inches) for Precipitation Gage 1071. .............................................................. 26 List of Figures Figure 1. Map of the basin study area. ............................................................................... 3 Figure 2. Map of LACDPW precipitation gages and evaporation stations used in this study. ............................................................................................... 6 Figure 3. Simulated carbon dioxide emissions scenarios used in CMIP3 projections (based on IPCC 2007)...................................................................... 7 Figure 4. Radiative forcing of the RCPs (emission runs used by CMIP5 projections, based on van Vuuren et al [2011]). ................................................. 8 Figure 5. Sets of downscaled projections used. ................................................................. 9 Figure 6. Map showing the NLDAS grid cells that correspond with the study area (crosses represent the center points of each grid cell). .................................... 11 Figure 7. Stylized example of a projection membership diagram. .................................... 14 Figure 8. Selection process for the BCSD climate scenarios. .......................................... 15 Figure 9. BCSD climate scenario selections for all six future periods. ............................. 16 Figure 10. Process to develop hourly precipitation time-series for each gage. ................ 17 Figure 11. Hourly time series repeated for each projection in each climate scenario. ..... 19 Figure 12. Hourly time series for all future time periods concatenated to provide one-time series. ................................................................................................ 19 Figure 13. Selecting CMIP5-BCCA projections from lowest and highest emission pathways (RCP2.6 and RCP8.5). ..................................................................... 21 Figure 14. Map of precipitation gage locations. ............................................................... 29 Figure 15. 24-hour, 1-in-50-year precipitation depths for the current climate, from NOAA Atlas 14 (Perica et al. 2012). ......................................................... 30 Figure 16. Change in 24-hour, 1-in-50-year precipitation depths in inches between the current climate (NOAA Atlas 14; Perica et al. 2012) and the minimum estimate from the BCSD projections for 2011 through 2099. ........................... 32 Figure 17. Change in 24-hour, 1-in-50-year precipitation depths in inches between the current climate (NOAA Atlas 14; Perica et al. 2012) and the minimum estimate from the CMIP5-BCCA projections for 2011 through 2099. ............... 32 Figure 18. Change in 24-hour, 1-in-50-year precipitation depths in inches between the current climate (NOAA Atlas 14; Perica et al. 2012) and the maximum estimate from the BCSD projections for 2011 through 2099. ........................... 33 Figure 19. Change in 24-hour, 1-in-50-year precipitation depths in inches between the current climate (NOAA Atlas 14; Perica et al. 2012) and the maximum estimate from the CMIP5-BCCA projections for 2011 through 2099. ............... 33 Appendices Appendix A: CMIP3-BCSD Projection Membership Diagrams and Projection Membership Tables Appendix B: CMIP5-BCSD Projection Membership Diagrams and Projection Membership Tables Appendix C: Storm Event Frequency Results ii Los Angeles Basin Study Task 3.1 Development of Climate-Adjusted Hydrologic Model Inputs Acronyms and Abbreviations °C degrees Celsius BCCA Bias-Correction Constructed Analogue BCSD Bias-Correction and Spatial Disaggregation CDF Cumulative Distribution Function CMIP3 Coupled Model Intercomparison Project,
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