Updated Precipitation Frequency Analysis for the State of Alaska

Abstract and project information last updated: 1 March 2011. Project updates are dated below.

AUTC
Project
Number
207120
Principal
Investigator
Amy Tidwell (UAF)
atidwell@alaska.edu
Funding
Agency

US Department of Transportation (RITA)

Alaska Department of Transportation & Public Facilities

Project
Budget
99400
Start
Date
1 July 2008
Estimated
End Date
30 June 2010

Abstract

Planning for construction of roads and bridges over rivers or floodplains includes a hydrologic analysis of rainfall amount and intensity for a defined period. Infrastructure design must be based on accurate rainfall estimates — how much (intensity), how long (duration), and how often (frequency or probability). UAF and the National Oceanic and Atmospheric Administration are updating this important design tool with support from AUTC and ADOT&PF. Measuring precipitation in an environment like Alaska’s is difficult. Challenges include poor gauge performance in windy environments, especially for solid precipitation (such as snow, sleet, and hail); and accessing and working in remote, sparsely populated, rough, and complex terrain. Another issue is the sparseness and distribution of the gauge stations. For example, the area north of the Brooks Range, known as the Arctic Slope of Alaska, is one of the least-understood climatic regions of the country. This region, with an area of over 230,000 square kilometers, has only a handful of long-term precipitation gauges, and many of the existing gauges are unattended. The quality of reported precipitation data varies due to gauge location, type, and whether or not a rain or snow gauge shield is present. Wildlife interactions with stations are a common occurrence in remote environments This project uses newer methodology and more advanced modeling techniques to analyze both the original data and the data collected since this information was last published in 1963. The team has compiled all data from the various resources, put it in a common format, and completed preliminary quality assurance and control. Due to a lack of detailed metadata, the proposed bias corrections for gauge undercatch will not be made (gauge history at each station did not indicate when or if alter shields were added). This study only addresses the frequency of rainfall events; thus, researchers will define the rainy season for each station using air temperature data. Another ongoing task is to determine which station data sets, of the roughly 1,243 meteorological stations and private rain gauges throughout Alaska, can be merged (stations essentially located at the same place but with different names and data collection dates). This new information will ultimately be published as Volume 14 of the NOAA Atlas, Precipitation-Frequency Atlas of the United States, in a spatially-distributed electronic format.