Groundwater briefing: Sep 2026

The Central Valley this month, from the map's latest refresh.

• Readings through Sep 2026. 798 monitoring wells were read in Jul–Sep 2026, 409 of them in the last month. More arrive late.
• Deeper than a year ago (subbasin averages): Pleasant Valley (21.2 ft), Madera (5.7 ft), Westside (5.5 ft).
• Shallower than a year ago: Tule (8.0 ft), Cosumnes (7.8 ft), Corning (4.9 ft).
• NOAA's outlook (issued Oct 2026) leans wet: 122 % of normal precipitation for water year 2027. Under it, all 34 subbasins are shallower in Sep 2027 than now.
• Valley kriged average now 138.9 ft below ground; Sep 2027 under the outlook's three precipitation runs: dry (85 %) 142.5 ft, central (122 %) 132.7 ft (80 % range 129.3–134.4), wet (166 %) 128.2 ft.
• 106 of 1,320 RMS wells read in the last year are below their minimum threshold. 19 GSAs meet their plan's undesirable-result rule now; under the outlook, 6 more do within 12 months.
• 101 wells are at their lowest reading on record.
• Typical miss at a well: 4.2 ft at 1 month, 7.0 ft at 12 (held-out tests). Most map wells were last read 3–12 months ago; there the 12-month miss is about 10 ft.

Cite

Gray, W. (2026). Central Valley Groundwater Map and Forecast, release 2026-09.5cdfad9c (readings through Sep 2026) [Data set]. CC BY 4.0. https://groundwater-map-175591637760.us-west1.run.app/release/2026-09.5cdfad9c

Built 2026-10-30 12:00 from release 2026-09.5cdfad9c. CC BY-NC 4.0 (cite Gray, W.).