Snow-departure vignette for the Kootenay Lake region (KOTL + LARL + DUNC + SLOC)

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Problem

The package's original climate-departure (KOTL) vignette ran the consumer pipeline on a single watershed group at single-watershed scale. That made the snow story underpowered — there's no climatic gradient inside one WSG, and no inherited geography for readers to anchor on. Now that snow vars exist (#48, v0.2.0) and the FWCP Peace vignette has demonstrated the regional-AOI pattern with per-ecoregion breakdowns and citation-grounded interpretation, the natural KOTL evolution is to expand the AOI to the four-WSG Kootenay Lake region and tell the snow story properly.

This supersedes the deferred KOTL decision in #49 with a concrete plan: keep KOTL as a worked example, expand its AOI, mirror the peace-fwcp.Rmd structure.

Scope

The new vignette uses a four-watershed-group AOI in the southern Kootenays:

WSG	Name	km²	Direction from Kootenay Lake
KOTL	Kootenay Lake	9,370	(anchor)
LARL	Lower Arrow Lake	6,612	W — includes Trail / Rossland / Red Mountain
DUNC	Duncan Lake	4,763	N — drains north end of Kootenay Lake (Duncan + Lardeau)
SLOC	Slocan River	3,431	NW — between Selkirks and Monashees

Total: ~24,200 km². Comparable to the FWCP Peace AOI (~73,000 km²) but more compact and focused on a single climatic theatre — the southern Selkirks and southwest Purcells around Kootenay Lake.

The east-west precipitation gradient across this AOI is the climatic backbone of the snow story:

• West / NW (LARL, SLOC): Selkirks west slope catches Pacific spillover precip via the Slocan/Lower Arrow openings. Deep maritime snowpack at high elevations.
• N / centre (DUNC, KOTL): Selkirks east slope + Kootenay Lake basin. High alpine snowpack (Purcell Wilderness Conservancy west, Selkirks east of the lake).
• E (KOTL east shore into the Purcells): rain shadow of the Selkirks, drier despite high elevation.

This gradient makes the snow story richer than at the Peace scale (where the gradient is mostly continental + latitudinal).

Vignette deliverables (mirror peace-fwcp.Rmd)

• New AOI bundled at inst/extdata/example_aoi_kootenay_lake.gpkg (union of the 4 WSGs from FWA via fresh::frs_db_conn() or bcdata)
• Bundled context layers at inst/extdata/context_kootenay_lake.gpkg — towns (Nelson, Castlegar, Trail, Rossland, Kaslo, Nakusp), lakes, rivers, highways, watershed groups, ecoregions clipped to AOI. Mirror data-raw/example_context_fwcp_peace.R.
• vignettes/kootenay-lake.Rmd — full vignette with sections matching the FWCP Peace template:
  • Area of Interest
  • Connect to the Data Catalog
  • Extract Climate Time Series
  • Trends
  • Daytime Highs and Overnight Lows
  • Snowpack (the headline section — seasonal-curve table + 4 annual scalars)
  • Recent vs Pre-warming
  • Spatial Pattern
  • Per-Ecoregion Variation (incl. snow per-ecoregion if signal differentiates)
  • Watershed Groups Across Ecoregions (4-WSG version)
  • Interpretation
  • References
• Bibliography reuse vignettes/references.bib from Snowpack-departure methodology lit review: rag-build + 11 papers + citation map #54 — same 11 papers cover the snow methodology for the Kootenays as for the Peace.
• Pre-compute via new data-raw/kootenay_lake_vignette_data.R mirroring data-raw/peace_fwcp_vignette_data.R. Bundled inst/vignette-data/kootenay_lake.rds.
• Drop the existing single-WSG vignettes/climate-departure.Rmd and any KOTL-only assets that aren't reused (the README quick-start still uses some KOTL polygons — keep those if they're the same WSG geometry).

Place names worth calling out in the prose

Anchor names readers will recognize:

• Kootenay Lake (centre) — Nelson, Kaslo, Crawford Bay
• Lower Arrow Lake / Slocan — Castlegar, Nakusp, Slocan, New Denver
• Trail / Rossland / Red Mountain — south LARL, lowest-elevation snow signal in AOI
• Duncan Lake / Lardeau valley — north of Kootenay Lake, alpine + ski-relevant terrain (Duncan, Argenta, Howser)
• Purcell Wilderness Conservancy — east edge of KOTL, alpine/ungulate habitat

Snow story angle

Particular things to test/report given the QA findings from #48:

• Per-WSG (or per-ecoregion-within-AOI) snow signal — does the east-west precip gradient produce different snow trends? In particular: do western WSGs (SLOC, LARL) show the deep-pack maritime signal, vs eastern KOTL/Purcell areas showing drier-trending snow?
• ASWS QA at Kootenay-region sites — extend data-raw/qa_snow_validation.R to the new AOI's sites (mostly the same bcsnowdata calls, different spatial filter).
• Salmon framing not relevant here either. Lower Columbia River below Hugh Keenleyside (Castlegar) is dam-fragmented; KOTL itself has Kootenay Lake gerrard rainbow trout (resident). FWCP Columbia Region supports resident salmonids + kokanee, not anadromous salmon. Use the same FWCP-Peace-style framing.

Out of scope

• Rockies / Elk Valley (BULL, ELKR) — different climatic regime, different reporting context (FWCP East Kootenay).
• Anadromous salmon framing.
• New methodology — reuse the v0.2.0 + Snowpack-departure methodology lit review: rag-build + 11 papers + citation map #54 stack.
• Updating the README quick-start beyond pointing at the new vignette (the existing single-WSG KOTL example assets stay in inst/extdata/ for the README).

Closes

Closes #49 (KOTL decision: keep + expand).