---
chapter:
  doi: 10.7930/J0H993CC
  identifier: precipitation-change
  number: 7
  report_identifier: climate-science-special-report
  sort_key: 9
  title: Precipitation Change in the United States
  url: https://science2017.globalchange.gov/chapter/7/
chapter_identifier: precipitation-change
cited_by: []
confidence: 'Based on the evidence and understanding of the issues leading to uncertainties, confidence is <em>high</em> that heavy precipitation events have increased in the United States. Furthermore, confidence is also <em>high</em> that the important regional and seasonal differences in changes documented in the text and in Figures 7.2, 7.3, and 7.4 are robust.'
contributors: []
evidence: 'The key finding and supporting text summarize extensive evidence documented in the climate science peer-reviewed literature. Numerous papers have been written documenting observed changes in heavy precipitation events in the United States, including those cited in the Third National Climate Assessment and in this assessment. Although station-based analyses (e.g., Westra et al. 2013<tbib>e941a5b9-10b7-462b-9042-5760a82fc415</tbib>) do not show large numbers of statistically significant station-based trends, area averaging reduces the noise inherent in station-based data and produces robust increasing signals (see Figures 7.2 and 7.3). Evidence of long-term changes in precipitation is based on analysis of daily precipitation observations from the U.S. Cooperative Observer Network (http://www.nws.noaa.gov/om/coop/) and shown in Figures 7.2, 7.3, and 7.4.'
files: []
gcmd_keywords: []
href: https://data.globalchange.gov/report/climate-science-special-report/chapter/precipitation-change/finding/key-finding-7-2.yaml
identifier: key-finding-7-2
ordinal: 2
parents:
  - activity_uri: ~
    label: 'figure -.2: Confidence / Likelihood'
    note: ''
    publication_type_identifier: figure
    relationship: prov:wasDerivedFrom
    url: /report/climate-science-special-report/chapter/front-matter/figure/confidence---likelihood
process: 'Based on numerous analyses of the observed record in the United States there is <em>high confidence</em> in the observed changes in heavy precipitation events, and <em>medium confidence</em> in observed changes in mesoscale convective systems.'
references:
  - href: https://data.globalchange.gov/reference/e941a5b9-10b7-462b-9042-5760a82fc415.yaml
    uri: /reference/e941a5b9-10b7-462b-9042-5760a82fc415
regions: []
report_identifier: climate-science-special-report
statement: 'Heavy precipitation events in most parts of the United States have increased in both intensity and frequency since 1901 (<em>high confidence</em>). There are important regional differences in trends, with the largest increases occurring in the northeastern United States (<em>high confidence</em>). In particular, mesoscale convective systems (organized clusters of thunderstorms)—the main mechanism for warm season precipitation in the central part of the United States—have increased in occurrence and precipitation amounts since 1979 (<em>medium confidence</em>).'
uncertainties: 'The main source of uncertainty is the sensitivity of observed precipitation trends to the spatial distribution of observing stations and to historical changes in station location, rain gauges, and observing practices. These issues are mitigated somewhat by methods used to produce spatial grids through gridbox averaging.'
uri: /report/climate-science-special-report/chapter/precipitation-change/finding/key-finding-7-2
url: ~