Annual precipitation reversal rates showed no clear change across 344 US divisions from 1901-1960 to 1966-2025
We tested whether annual precipitation reversals between local dry and wet tails changed across 344 US climate divisions. NOAA nClimDiv water-year totals gave 1,596 reversals in 1901-1960 and 1,517 in 1966-2025. With local 20th and 80th percentiles set within each period, the rate fell from 7.86% to 7.47%. The late-minus-early change was -0.39 percentage points. Its conditional 95% five-edge block interval was -2.48 to +1.74 points. A national year-field shuffle gave a two-sided p value of 0.6455 for the change relative to its exact reference mean. Pooled thresholds changed the point sign to +0.39 points, but its interval also included zero. All five planned setting checks had intervals that included zero. Thus, this annual precipitation measure did not resolve a change in reversal frequency. The result does not establish equal rates or test water-balance whiplash, flood risk, storage recovery, or a climate cause. Threshold choice, annual aggregation, source error and long climate cycles limit inference. Code, input data, derived evidence, an audit and repeat instructions are supplied.
precipitation · annual reversals · threshold choice · nClimDiv · null result · water year
References
8- usesAnnual dry-to-wet and wet-to-dry precipitation rates had no clear difference across 344 US divisions in 1901-2025 sci:sha256:014d2e4cfdb6c25691f20e02935f5bcda8296b061b914abf06373fd6fe6cec3b
Prior national direction test sets the context. We test a change between periods, which that study did not test. Data overlap is complete; this is not independent replication.
- usesThe largest three-year dry footprint across 344 US divisions was within a shuffled-year range in 1896-2025 sci:sha256:4915f54da906833901fc31c7361a80136ab32637c2fc0d66979bcf92a5a5f51e
Source format document and national field-shuffle context.
- reviewsdoi:10.1038/s43017-024-00624-z
- reviewsdoi:10.1029/2025WR041240
- usesdoi:10.1175/JAMC-D-13-0248.1
- useshttps://www.ncei.noaa.gov/monitoring-content/data/us/climdiv/monthly/current/climdiv-pcpndv-v1.0.0-20261006
- useshttps://www.ncei.noaa.gov/access/metadata/landing-page/bin/iso?id=gov.noaa.ncdc%3AC00005
- usesRandom year order matched winter precipitation transition rates in seven California divisions in 1901-1960 and 1966-2025 sci:sha256:2f2f4ab7b44786e4f57f75ccfbe3b605335ce8e5c23269b6d38df259a2792d98
Prior seven-division winter comparison used the same periods and a tail-count reference. We extend the scope to annual precipitation across 344 divisions; this is not a new decomposition method.
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