Santa Barbara staff present lower 2025 water demand baseline and seven-scenario demand envelope

Jasmine Showers, the staff presenter, told the Santa Barbara City Water Commission that the draft 2025 urban water management plan (UWMP) baseline projects lower potable demand than the plan adopted in 2020 and that the city has developed a seven-scenario demand envelope to capture uncertainty through 2050.

“Baseline demands now include the effect of water conservation programs and more detailed water loss,” Showers said, explaining that the 2025 baseline draws on average water use from 2021 through 2024 rather than the pre-drought assumptions used in 2020. She said the 2020 projection assumed a rebound toward 90% of pre-drought use; observed use since 2021 has been lower, producing a smaller 2025 baseline.

Showers quantified the change: the 2020 potable-demand projection reached about 12,500 acre-feet per year by 2050, while the 2025 baseline projects closer to 10,000 acre-feet per year — a difference of roughly 3,000 acre-feet annually by mid-century. The presentation included recycled-water use and planned sales to Montecito Water District in all scenarios.

The staff presentation stressed that the baseline is the most plausible single trajectory, but that planners need a demand envelope to reflect alternative futures. The envelope includes scenarios for higher housing growth (aligned with RHNA allocations of 8,000 units for 2023–2031), slower housing growth (the city housing element assumes about 3,100 units in the same period), faster or slower job-driven commercial demand (+/−20% applied to commercial users), climate-driven increases using Cal‑Adapt projections, the effect of adopted water-rate increases, and a stacked “demand creep” upper bound.

On rates, Showers said the city’s 2024 rate study includes 10.5% increases in 2025–2026 and 10% increases in 2027–2028, with a 5% assumption in later years for modeling. The team used a price-elasticity value of −0.11, which, applied annually in the model, produces a scenario about 11% below baseline by 2050; staff cautioned that approach may be conservative because of demand hardening.

Using Cal‑Adapt data, the climate scenario in the envelope assumed a 1.4°F increase from 2025 to 2050 and applied an estimate that a 1°F rise in temperature increases outdoor demand by approximately 5%, producing roughly a 2% increase versus baseline by 2050 in that scenario. The demand‑creep upper bound — a stack of upward pressures such as tourism, hotter weather, and faster job growth — could reach roughly 31% above baseline (including recycled water and Montecito sales) by 2050, staff said.

Showers also reviewed the city’s adaptive management matrix from the 2020 consolidated plan. Staff said the commission is currently below Phase 1 (tracking and managing demand) and described mandatory triggers in later phases: for example, desalination expansion would be triggered at about 13,000 acre-feet of potable demand or an approximate 20% supply reduction. At higher phases, staff said conservation measures would become mandatory and desalination or other new supplies would be implemented.

Commissioners questioned the assumed start point for projections, whether conservation measures produce permanent behavioral change, and the mix of housing types underlying growth scenarios. Showers said recent permitting data shows roughly 68% of new permitting was for multifamily construction and acknowledged uncertainty around behavioral rebound, noting the demand scenarios were developed with an experienced consulting firm.

The UWMP update is part of the city’s consolidated planning through 2050; staff said the updated baseline and demand-envelope work will inform the UWMP due July 1, 2025. No formal action was required on the demand update at this meeting.