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Climate 2017, 5(1), 10; doi:10.3390/cli5010010

Precipitation Intensity Trend Detection using Hourly and Daily Observations in Portland, Oregon

Department of Geography, Portland State University, Portland, OR 97201, USA
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Academic Editors: Daniele Bocchiola, Claudio Cassardo and Guglielmina Diolaiuti
Received: 23 September 2016 / Revised: 5 February 2017 / Accepted: 13 February 2017 / Published: 18 February 2017
(This article belongs to the Special Issue Impact of Climate Change on Water Resources)
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Abstract

The intensity of precipitation is expected to increase in response to climate change, but the regions where this may occur are unclear. The lack of certainty from climate models warrants an examination of trends in observational records. However, the temporal resolution of records may affect the success of trend detection. Daily observations are often used, but may be too coarse to detect changes. Sub-daily records may improve detection, but their value is not yet quantified. Using daily and hourly records from 24 rain gages in Portland, Oregon (OR), trends in precipitation intensity and volume are examined for the period of 1999–2015. Daily intensity is measured using the Simple Daily Intensity Index, and this method is adapted to measure hourly scale intensity. Kendall’s tau, a non-parametric correlation coefficient, is used for monotonic trend detection. Field significance and tests for spatial autocorrelation using Moran’s Index are used to determine the significance of group hypothesis tests. Results indicate that the hourly data is superior in trend detection when compared with daily data; more trends are detected with hourly scale data at both the 5% and 10% significance levels. Hourly records showed a significant increase in 6 of 12 months, while daily records showed a significant increase in 4 of 12 months at the 10% significance level. At both scales increasing trends were concentrated in spring and summer months, while no winter trends were detected. Volume was shown to be increasing in most months experiencing increased intensity, and is a probable driver of the intensity trends observed. View Full-Text
Keywords: climate; precipitation intensity; hourly precipitation; hydrology; trend analysis climate; precipitation intensity; hourly precipitation; hydrology; trend analysis
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Cooley, A.; Chang, H. Precipitation Intensity Trend Detection using Hourly and Daily Observations in Portland, Oregon. Climate 2017, 5, 10.

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