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Open AccessArticle

Observed and Projected Precipitation Changes over the Nine US Climate Regions

Los Alamos National Laboratory, Earth and Environmental Sciences, Los Alamos, NM 87545, USA
Los Alamos National Laboratory, Theoretical Biology and Biophysics, Los Alamos, NM 87545, USA
Department of Physics, New Mexico State University, Las Cruces, NM 88003, USA
Author to whom correspondence should be addressed.
Atmosphere 2017, 8(11), 207;
Received: 27 July 2017 / Revised: 19 October 2017 / Accepted: 21 October 2017 / Published: 25 October 2017
(This article belongs to the Special Issue Global Precipitation with Climate Change)
We analyze the past (1900–2015) temperature and precipitation changes in nine separate US climate regions. We find that the temperature increased in a statistically significant (95% confidence level equivalent to alpha level of 0.05) manner in all of these regions. However, the variability in the observed precipitation was much more complex. In the eastern US (east of Rocky Mountains), the precipitation increased in all five climate regions and the increase was statistically significant in three of them. In contract, in the western US, the precipitation increased in two regions and decreased in two with no statistical significance in any region. The CMIP5 climate models (an ensemble mean) were not able to capture properly either the large precipitation differences between the eastern and the western US, or the changes of precipitation between 1900 and 2015 in eastern US. The statistical regression model explains the differences between the eastern and western US precipitation as results of different significant predictors. The anthropogenic greenhouse gases and aerosol (GHGA) are the major forcing of the precipitation in the eastern part of US, while the Pacific Decadal Oscillation (PDO) has the major influence on precipitation in the western part of the US. Our analysis suggests that the precipitation over the eastern US increased at an approximate rate of 6.7%/K, in agreement with the Clausius-Clapeyron equation, while the precipitation of the western US was approximately constant, independent of the temperature. Future precipitation over the western part of the US will depend on the behavior of the PDO, and how it (PDO) may be affected by future warming. Low hydrological sensitivity (percent increase of precipitation per one K of warming) projected by the CMIP5 models for the eastern US suggests either an underestimate of future precipitation or an overestimate of future warming. View Full-Text
Keywords: precipitation; climate models; regression models; future projections precipitation; climate models; regression models; future projections
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Chylek, P.; Dubey, M.K.; Hengartner, N.; Klett, J.D. Observed and Projected Precipitation Changes over the Nine US Climate Regions. Atmosphere 2017, 8, 207.

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