Deprecate and remove the `nadp` module (target: 2026-11-01)

[thodson-usgs]

Proposal

Deprecate the dataretrieval.nadp module now and remove it from the package on or after 2026-11-01 (six months from today, 2026-05-01).

A deprecation PR adding DeprecationWarnings to each public function in nadp.py is open at #243 — this issue will be updated once that PR is merged so the warning ship-status is visible from one place.

Justification

• Scope. dataretrieval is a USGS water-data package. NADP (the National Atmospheric Deposition Program) is hosted by the University of Wisconsin–Madison's State Lab of Hygiene, not USGS. Maintaining a third-party data fetcher in this package is outside the project's scope, and divergence between NADP's site layout and our wrapper has historically been a source of breakage (the existing tests in tests/nadp_test.py were added precisely because an upstream path change silently broke the module).
• Maintenance state. The module is small (~200 lines) and lightly maintained. The TODOs in the module docstring — "include AIRMoN, AMNet, and AMoN", "flexible handling of strings for parameters and measurement types", "add error checking", "add tests" — have been there for years and have not been picked up.
• Different shape from the rest of the package. Every other module in dataretrieval returns tabular data (DataFrames). nadp returns paths to extracted zipped GeoTIFFs — a fundamentally different use case, and one users can serve directly with a few lines of requests + zipfile against https://nadp.slh.wisc.edu/.
• Precedent. This follows the same pattern recently used for the waterwatch module (deprecated, then removed in Remove waterwatch module #228).

Timeline

Date	Milestone
2026-05-01	Deprecation PR opened (#243). Each public function in nadp.py emits a DeprecationWarning on call.
TBD	PR #243 merged → deprecation warning shipped in the next release.
2026-11-01	Earliest date the nadp module may be removed from dataretrieval. A separate removal PR will be opened on or after this date.

Migration guidance for users

Users currently depending on dataretrieval.nadp should fetch NADP zip/TIFF artifacts directly from https://nadp.slh.wisc.edu/ — the URL patterns the module hard-codes (https://nadp.slh.wisc.edu/filelib/maps/...) are stable and trivially reproducible with requests + zipfile. We're happy to host a short snippet in NEWS.md or the docs if there's demand; please comment on this issue if so.

Tracking

• Deprecation PR: Deprecate nadp module #243 (status will be reflected here once merged)
• Follow-up removal PR: not yet opened; will be filed on or after 2026-11-01

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