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New Zealand weather extremes and climate-related events; a model-based assessment

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thesis
posted on 23.11.2021, 21:32 by Nistor, Ben

Extreme weather and climate-related events can have pronounced environmental, economic and societal impacts, yet large natural variability within Earth’s constantly evolving climate system challenges the understanding of how these phenomena are changing. Increasingly powerful climate models have made it possible to study how certain factors, including anthropogenic forcings, have modified the likelihood and magnitude of extreme events.  This study examines climate observations, reanalysis fields and model output to assess how weather extremes and climate-related events have changed. Part 1 investigates the detection and attribution of surface climate changes in relation to ozone depletion. Part 2 uses probabilistic event attribution and storyline frameworks to evaluate the role of anthropogenic forcings in altering the risk of extreme 1-day rainfall (RX1D) events for Christchurch, New Zealand in light of an unprecedented rainfall event that occurred in March 2014.  Extremely large simulations of possible weather generated by the weather@home Australia-New Zealand (w@h ANZ) model found ozone forcings induced significant changes globally (< 3 hPa) in simulations of mean sea level pressure for 2013. A clear seasonal response was detected in the Southern Hemisphere (SH) circulation that was consistent with prior studies. Ozone-induced changes to average monthly rainfall were not significant in New Zealand with large natural variability and the limitation of one-year simulations challenging attribution to this climate forcing.  In Christchurch, model and observational data give evidence of human activity increasing the likelihood and magnitude (+17%) of RX1D events despite significant drying trends for mean total rainfall (-66%) in austral summer. For events similar to that observed during March 2014, the fraction of attributable risk (FAR) is estimated to be 27.4%. This result was robust across different spatial averaging areas though is sensitive to the rainfall threshold examined. Unique meteorological conditions in combination with anomalously high sea surface temperatures (SSTs) in the tropical South Pacific were likely important to the occurrence of this extreme event. These results demonstrate how human influence can be detected in present-day weather and climate events.

History

Copyright Date

01/01/2018

Date of Award

01/01/2018

Publisher

Te Herenga Waka—Victoria University of Wellington

Rights License

Author Retains Copyright

Degree Discipline

Physical Geography

Degree Grantor

Te Herenga Waka—Victoria University of Wellington

Degree Level

Masters

Degree Name

Master of Science

ANZSRC Type Of Activity code

3 APPLIED RESEARCH

Victoria University of Wellington Item Type

Awarded Research Masters Thesis

Language

en_NZ

Victoria University of Wellington School

School of Geography, Environment and Earth Sciences

Advisors

Renwick, James; Rosier, Suzanne