Pilot Creek runoff vs. Sierra snowpack

SMUD upper-watershed analysis — does decreasing high-altitude snowpack show up in Pilot Creek runoff? Data: USGS gauges + NCEI GHCN snow depths. Generated 2026-10-05.

+0.13r (runoff vs max snow, 1961–2008, n=38)
-0.037 cm/yrNetwork max-snow long-run trend (1900–2026)
+0.002 cm/yrMax-snow trend inside 1961–2008 window
1900–2026Snow-station record span (GHCN)
Bottom line: Over the 1961–2008 window that the Pilot Creek gauges cover, high-altitude snowpack is essentially flat (network max snow depth ≈ constant, March SWE ≈ constant). So within that window, snowpack decline is not the driver of runoff change. But on the full record back to 1900, the 11-station network shows a real, measurable decline in maximum snow depth (~-0.037 cm/yr) and in the high-elevation March SWE proxy (~-0.041 cm/yr) — consistent with your hypothesis, just operating on a longer timescale than the ~48-year gauge record can resolve.

1. Pilot Creek annual runoff with snowpack overlay (1961–2008)

Bars = Pilot Creek water-year runoff (Mm³, USGS 11431800/11433040). Gold dashed line = high-elevation March max snow depth (cm) — a SWE proxy at the peak-SWE season. Runoff is dominated by storm/season timing within the window, not a long-term snowpack trend.

64.851.938.925.913019611970198019891999200835828621514371.60High-elev max snow (cm)Pilot Creek runoff (Mm³/wy)Water year

2. Runoff vs. max snowpack (1961–2008)

Annual runoff (x) vs. network max snow depth (y) for the 48 water years. +0.13 correlation — the year-to-year snow depth in these mid-elevation stations is only weakly tied to Pilot Creek runoff. Dashed = linear fit.

Pilot Creek annual runoff (Mm³/wy)Network max snow depth (cm)

3. The long-run signal: snowpack since 1900

This is where the decline is visible. Network max snow depth (left) and high-elevation March SWE proxy (right), full GHCN record 1900–2026. Both trend down; the March SWE proxy — closer to what the upper Pilot basin actually holds — declines about -0.041 cm/yr.

Water yearNetwork max snow depth (cm)
Water yearHigh-elev March SWE proxy (cm)

4. Measurement locations

Red squares = USGS flow gauges on Pilot Creek. Dots = 11 GHCN snow-depth stations (colored by elevation, blue=low → red=high). Faint blue outlines = the SMUD upper-watershed (UARP) catchments. The snow stations sit on the eastern Sierra crest / western Nevada — the highest ones (Tahoe City, Glenbrook, Bowman Dam, Lake S. Paulding, Sierra Ville, Boca, Portola) are the best SWE proxies for the upper Pilot basin.

-121°-120°39°40°CA QUINCYCA SUSANVILLE 2SWCA BOWMAN DAMCA SIERRAVILLE RSCA PORTOLACA LAKE SPAULDINGCA BOCACA TAHOE CITYNV GLENBROOKNV CARSON CITYNV MINDEN1143180011433040
TypeIDNameLatLonElev (m)
Gauge11431800PILOT C AB STUMPY MEADOWS RES CA38.8946257-120.5682585—
Gauge11433040PILOT C BL MUTTON CANYON NR GEORGETOWN CA38.92351348-120.6418716—
SnowUSC00047195CA QUINCY39.937-120.9481042
SnowUSC00048702CA SUSANVILLE 2SW40.417-120.6631284
SnowUSC00041018CA BOWMAN DAM39.454-120.6561641
SnowUSC00048218CA SIERRAVILLE RS39.583-120.3711516
SnowUSC00047085CA PORTOLA39.805-120.4721478
SnowUSC00044713CA LAKE SPAULDING39.318-120.6391572
SnowUSC00040931CA BOCA39.389-120.0941699
SnowUSC00048758CA TAHOE CITY39.168-120.1431899
SnowUSC00263205NV GLENBROOK39.075-119.9411936
SnowUSC00261485NV CARSON CITY39.125-119.7681451
SnowUSC00265191NV MINDEN38.955-119.7761435

5. Download the data (CSV)

Everything above, as raw CSV.

pilot_creek_annual_runoff.csvPilot Creek annual runoff (water year, Mm³)pilot_creek_runoff_vs_snowpack.csvPilot Creek runoff vs high-elev March SWE (1961–2008)snow_network_longrun.csvNetwork max snow + high-elev March SWE (full record 1900–2026)snow_stations_longrun.csvPer-station max snow depth (all 11 stations, full record)usgs_11431800_daily_cfs.csvUSGS 11431800 daily discharge (CFS), Pilot Creek abv Stumpy Meadowsusgs_11433040_daily_cfs.csvUSGS 11433040 daily discharge (CFS), Pilot Creek abv Mutton Canyonsnow_USC00047195_annual_max.csvCA QUINCY — annual max snow depth (cm)snow_USC00048702_annual_max.csvCA SUSANVILLE 2SW — annual max snow depth (cm)snow_USC00041018_annual_max.csvCA BOWMAN DAM — annual max snow depth (cm)snow_USC00048218_annual_max.csvCA SIERRAVILLE RS — annual max snow depth (cm)snow_USC00047085_annual_max.csvCA PORTOLA — annual max snow depth (cm)snow_USC00044713_annual_max.csvCA LAKE SPAULDING — annual max snow depth (cm)snow_USC00040931_annual_max.csvCA BOCA — annual max snow depth (cm)snow_USC00048758_annual_max.csvCA TAHOE CITY — annual max snow depth (cm)snow_USC00263205_annual_max.csvNV GLENBROOK — annual max snow depth (cm)snow_USC00261485_annual_max.csvNV CARSON CITY — annual max snow depth (cm)snow_USC00265191_annual_max.csvNV MINDEN — annual max snow depth (cm)

6. Sources & documentation

Runoff (USGS NWIS):

USGS 11431800 — Pilot Creek above Stumpy Meadows Res (daily discharge, 00060) USGS 11433040 — Pilot Creek above Mutton Canyon (daily discharge, 00060) USGS NWIS discharge parameter documentation

Snow depth (NCEI GHCN-Daily, element SNWD):

NCEI National Snow Data Center / GHCN-D GHCN station inventory (lat/lon/elev/names)

Catchments: SMUD UARP upper-watershed DEM catchments (data/derived/dem/catchments_webmap.geojson). Plant throughput: CEC 2101 annual generation 2002–2012 + FERC official heads (see data/derived/plants_official.csv).

Method & caveats

Generated for SMUD hydro analysis · data pulled live from USGS NWIS & NCEI GHCN