Year

2024

Degree Name

Doctor of Philosophy

Department

School of Earth, Atmospheric and Life Sciences

Abstract

Alaska has one of the largest glaciated areas in the world, which is highly sensitive to climate change. Currently, the mass loss from Alaskan glaciers contributes to about a third of global mean sea level rise. Tidewater glaciers contribute non-linearly to global mean sea level rise through their rapid retreat. Although internal controls strongly influence the tidewater glacier cycle, the ubiquitous retreat of Alaskan tidewater glaciers indicates climatic forcing is involved. Meteorological observations from this region are insufficient to assess the climatic influence across a tidewater glacier cycle, and existing model datasets are either too coarse or cover too short a time period. This project reconstructs the regional climate of southern Alaska by downscaling the NOAA-CIRES-DOE 20th Century Reanalysis (20CRv3) from 1837–2015. The Weather Research and Forecasting model (WRF) was used to downscale the reanalysis data to produce high-resolution 4-km (convection-permitting) output. The focus of this study is on Southern Alaska and the areas around the Columbia Glacier and Glacier Bay. For 2010, five physics parameterisations were tested and evaluated using Global Surface Summary of the Day (GSOD) observational records to choose an appropriate model set-up for the region. The different physics configurations showed similar results. The leading parameterisation for temperature and precipitation was used to downscale the 179-year 20CRv3 dataset to reconstruct local climate and weather over southern Alaska over a significant part of a tidewater glacier cycle. The 20CRv3 downscaling was evaluated for the modern-day period (1981-2015) against the GSOD and PRISM (Parameter-elevation Regression on Independent Slopes Model) observational datasets for Alaska and compared to ERA5 reanalysis output. The 20CRv3-WRF performs well for annual mean temperature (0.61≤r≤0.96) and moderately well for annual accumulated precipitation (0.16≤r≤0.76) compared to station observations. Over the full time period (1837-2015), temperatures for all regions increased, especially in winter and autumn. Precipitation also increased overall but showed a slight decrease for the modern-day climate (1986-2015). For Columbia Glacier, a change in the rain-to-snow ratio with an increase in liquid precipitation was found. Our results show that 20CRv3-WRF is a suitable high-resolution dataset to assess the influence of climate on tidewater glaciers in southern Alaska for the downscaling period (1837–2015). The downscaling product produced here provides a suite of variables including temperature, precipitation, energy surface fluxes, wind speed, and more that can support different approaches of glacier modelling as well as studies within other fields that require high-resolution, long-term atmospheric data.

FoR codes (2008)

0401 ATMOSPHERIC SCIENCES, 040602 Glaciology, 0499 OTHER EARTH SCIENCES

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.