Incorporating the Costs and Benefits of Adaptation Measures in Preparation for Extreme Weather Events and Climate Change—Guidebook (2020)

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153 The following presents a blank Level 1 worksheet. Level 1: Climate-Adapted Benefit-Cost Analysis This is an approximate test to see if it would be cost-effective to upgrade assets to the future conditions posed by climate change. Current Conditions A P P E N D I X I Blank Level 1 Worksheet Step 1. Determine return periods. Description Variable Value Largest return period for which there will be no damage (Design Return Period) Tcnd (years) Return period associated with an event that would cause moderate but considerable structural damage, or roadway flooding and traffic interruption. This would be the next-highest standard return period to Tnd Tcmod (years) Return period for which damage would be practically maximized Tcmax(years) Step 2. Determine damages associated with Step 1. Total damages associated with Tcnd Dcnd ($) Total damages associated with Tcmod (e.g., loss of riprap, short- term road closure, traffic control and road cleanup costs) Dcmod ($) Total damages associated with Tcmax (i.e., failure of the hydraulic structure leading to large structural damage and loss of road service and possibly injuries or fatalities) Dcmax ($) Present value coefficient for the remaining project useful life (i.e., remaining service life during the period of projected climate change) from Appendix B PVC (%)

154 Incorporating the Costs and Benefits of Adaptation Measures in Preparation for Extreme Weather Events and Climate Change—Guidebook Step 3. Determine current discharge flows associated with Step 2. Associate discharges with return period, Tcnd under current (no climate change) conditions Qcnd (cfs) Associate discharges with return period, Tcmod under current (no climate change) conditions Qcmod (cfs) Associate discharges with Tcmax under current (no climate change) conditions Qcmax (cfs) Step 4. Calculate expected annual damages between Tcnd and Tcmod based on Step 1 and Step 2. = * ( − ) Step 5. Calculate expected annual damages between Tcmod and Tcmax based on Step 1 and Step 2. = * ( − ) Step 6. Calculate total Annualized Damages. = +

Blank Level 1 Worksheet 155 Step 7. Calculate present value of total expected damages under current conditions. = * Note: PVC can be determined based on Appendix B. Step 8. Summarize the data for current climate conditions. Tc(years) Dc($) Qc(cfs) Dac($) Tcnd Tcmod Tcmax Total annualized damages Step 9. Plotting • Create a graph by plotting the return periods Tcnd, Tcmod, and Tcmax (Step 8) on a logarithmic scale on the x-axis against the associated discharges on the y-axis. • Create a second graph by plotting the discharges on the x-axis (with a “normal” scale as opposed to logarithmic) and the estimated damages (D) (Step 8) associated with each discharge on the y-axis.

158 Incorporating the Costs and Benefits of Adaptation Measures in Preparation for Extreme Weather Events and Climate Change—Guidebook Calculate future flows and associated expected damage for future climate conditions. To do this, start by identifying the climate change scenario to be used for analysis (see Chapter 3). For the selected climate scenario, calculate the estimated future discharges for each return period (i.e., return period in which no damage occurs, return period in which moderate damage occurs, and return period in which significant damage occurs). This will result in identifying values for Qf1, Qf3, and Qf5. Step 10. Calculate the future flows for selected return periods. Description Variable Value Associate discharges with return period, Tfnd (i.e., Tnd) based on climate change conditions Qfnd Associate discharges with return period, Tfmod (i.e., Tmod) based on climate change conditions Qfmod Associate discharges with Tf5 (i.e., Tfmax) based on based on climate change conditions Qfmax Step 11. Plotting: Summarize the current and future flows for each return period. Tc(years)* Qc (cfs)* Tf (years) Qf (cfs) *See Step 8 Plot the future discharges under the selected climate change scenario Qfnd, Qfmod, and Qfmax on the same logarithmic graph as the baseline conditions (see Step 9). Step 12. Calculate the Future Return period for the selected climate scenario based on Step 11. This provides an estimate of the climate-adjusted return period for the base flow. = − − * − − = 10 ______________________________________________________________

Blank Level 1 Worksheet 159 Step 13. Interpolate the damages ( ) linearly based on revised future discharges (Step 11) using the equations below. = + − ( − ) * ( − ) = _____________________________________________ Step 14. Interpolate the damages ( ) linearly based on revised future discharges (Step 11) using the equations below. = + − ( − ) * ( − ) = ___________________________________________________ Step 15. Interpolate the damages ( ) linearly based on revised future discharges (Step 11) using the equations below. = + − * = ___________________________________________________

160 Incorporating the Costs and Benefits of Adaptation Measures in Preparation for Extreme Weather Events and Climate Change—Guidebook Step 16. Summarize the climate-adjusted values for discharge and damages. Set the future damages (Dfnd) corresponding to Tfnd to $0, as this value corresponds to the same discharge as Qcnd (i.e., Qcnd=Qfnd ). Tf Df ($) Qf (cfs) Tfnd T’fnd Tfmod Tfmax Step 17. Plot the damages against the peak discharges on the same regular graph paper as for the previous figure to develop a curve for climate-adjusted flows. Step 18. Calculate the annualized damages for climate-adjusted conditions using a similar approach to the previous section, substituting the climate-adjusted values for the current condition values based on Step 16. = * ( − ) = _____________________________________________________________________ Step 19. Calculate the annualized damages for climate-adjusted conditions using a similar approach to the previous section, substituting the climate-adjusted values for the current condition values based on Step 16. = + 2 * ( 1 − 1 ) =____________________________________________________________________ Step 20. Calculate the annualized damages for climate-adjusted conditions using a similar approach to the previous section, substituting the climate-adjusted values for the current condition values based on Step 16. = + 2 * ( 1 − 1 ) = ___________________________________________________________________

Blank Level 1 Worksheet 161 Step 21. Calculate the annualized damages for climate-adjusted conditions using a similar approach to the previous section, substituting the climate-adjusted values for the current condition values. = + + = $_______________________________________________________________________ Step 22. Calculate the annualized damages for climate-adjusted conditions using a similar approach to the previous section, substituting the climate-adjusted values for the current condition values. = * = _______________________________________________________________________ Step 23. Summarize the climate-adjusted values. Tf Qf (cfs) Df ($) Daf ($) Tfnd T’fnd Tfmod Tfmax Step 24. Compare the additional damages for the base case with and without climate adjustment using the base case damages calculated in Step 7 and climate-adjusted damages calculated in Step 22. ∆ = − ∆ = ______________________________________________________________________ This value represents the additional present value of the expected damages from climate change during the asset’s remaining useful life. A resilience/mitigation measure aimed at main- taining the current frequency-damage structure (design level) while accounting for climate change must cost less than this value to be cost-effective.