*3.2. Scenario Definitions*

Scenarios are developed to explore the energetic tradeoffs of increasing local water supplies over 5-year increments for years spanning 2020 through 2050. We define two scenarios for average weather year conditions (S1, S2), and two additional scenarios (S3, S4) to simulate future water supplies in a single dry year (that assume similar hydrology to 2014/2015), as a proxy for future possible droughts. In these scenarios, S1 and S3 reflect LADWP's most recent water portfolio trajectory from 2020 to 2040

in the utility's 2015 UWMP [7]; however, we extrapolate projections for years of 2045 and 2050. S2 and S4 are developed to simulate a more aggressive local water supply portfolio to represent the newer water policy targets of the Los Angeles City's Green New Deal, which are not reflected in the 2015 UWMP [24]. The scenarios are described in Table 2.


**Table 2.** Description of scenarios analyzed in this study.

For S2, we consider the maximum cost-effective conservation potential reported in LADWP's water conservation potential study [37] for the years spanning 2020 and 2035, and we assumed 2% additional conservation for each subsequent five year block thereafter (i.e., for 2040, 2045 and 2050). (Based on LADWP's water conservation potential study [37], cost-effective conservation is defined as the level of water savings achievable through cost-effective conservation programs implemented by LADWP, but it would require customer engagemen<sup>t</sup> through expanded financial incentives.) For S4, we assume that water savings in dry years exceed conservation volumes in average weather years due to factors such as more aggressive voluntary and involuntary conservation measures and other water saving ordinances. For stormwater, the cumulative centralized stormwater capture potential reflects LADWP's stormwater capture master plan [38]. To meet the City of Los Angeles' 100% wastewater recycling goal [24], we assume that 60% of the current volume of discharged effluent from wastewater treatment facilities will be further treated according to IPR standards for future groundwater recharge projects by 2035. The remaining 40% is assumed to be treated for environmental use. We exclude any potential water supply from seawater desalination, as LADWP does not include desalinated seawater as part of its future water portfolio [7,16]. Water demand volumes are kept constant in each set of scenarios, such that S1–S2 and S3–S4 reflect water demand volumes in LADWP's 2015 UWMP for an average year and single-dry year, respectively [7]. Figure 3 illustrates LADWP's water portfolio for a historical average year (i.e., ref.), as well as the assumed water portfolios for S1–S4.

**Figure 3.** Historical reference year and projected water supply portfolios in S1–S4. Water supplies from LAA (Los Angeles Aqueduct), MWD (Metropolitan Water District), CON (conservation), GW (groundwater), IPR (indirect potable reuse), NPR (non-potable reuse) and STW (stormwater capture for direct use) balance LADWP's historical or projected water demand, and ENV includes recycled water that goes into environmental services.
