{"id":{"repo_id":"vt","oai_identifier":"oai:vtechworks.lib.vt.edu:10919/140763"},"canonical_url":"https://search.dev.ndltd.org/etd/vt/oai:vtechworks.lib.vt.edu:10919/140763","repository":{"repo_id":"vt","name":"Virginia Tech","base_url":"https://vtechworks.lib.vt.edu/oai/request"},"display":{"title":"Analysis of Variability in Atmospheric River Characteristics in New Zealand from 1940 through 2023","abstract":"Atmospheric rivers (ARs) are long, narrow corridors of concentrated atmospheric moisture that transport water vapor from the tropics to the middle latitudes where they can drive extreme precipitation and flooding. They have become especially important for New Zealand where ARs are critical for their water resources but also cause societal impacts. This study examines long-term changes in AR frequency, seasonality and strength in New Zealand across a pre-satellite era (1940–1978), satellite era (1979–2023), and modern climate reference period (1991–2020) to account for shifts in observational capability following the advent of satellite data in 1979. ERA5 reanalysis was used to create a regionally tailored atmospheric river detection technique (ARDT) to identify and track ARs across the three periods. The ARDT classified ARs using the 85th and 95th percentiles of integrated vapor transport (IVT) to isolate moderate and extreme ARs and assess their sensitivity across the three periods. Mann-Kendall tests were produced to analyze trends in AR strength and size across the three periods, while Mann-Whitney U tests compared AR strength across the three periods. Additional analyses looked at the contribution of extreme landfalling ARs to high-intensity 6-hourly in-situ precipitation recorded at two high-fidelity stations in New Zealand. Results indicate that extreme ARs are showing the most consistent increasing trends across all three periods, especially the satellite and reference period. Mann-Whitney U tests exhibit statistically significant differences primarily between the pre-satellite and reference period and extreme landfalling ARs account for a disproportionate share of the most intense precipitation events. These findings suggest that extreme ARs provide the most informative lens for understanding future AR impacts in New Zealand and, in the context of independent projections showing future increases in AR-induced extreme precipitation, highlight the importance of resilience planning and adaptive decision-making.","abstract_html":"Atmospheric rivers (ARs) are long, narrow corridors of concentrated atmospheric moisture that transport water vapor from the tropics to the middle latitudes where they can drive extreme precipitation and flooding. They have become especially important for New Zealand where ARs are critical for their water resources but also cause societal impacts. This study examines long-term changes in AR frequency, seasonality and strength in New Zealand across a pre-satellite era (1940–1978), satellite era (1979–2023), and modern climate reference period (1991–2020) to account for shifts in observational capability following the advent of satellite data in 1979. ERA5 reanalysis was used to create a regionally tailored atmospheric river detection technique (ARDT) to identify and track ARs across the three periods. The ARDT classified ARs using the 85th and 95th percentiles of integrated vapor transport (IVT) to isolate moderate and extreme ARs and assess their sensitivity across the three periods. Mann-Kendall tests were produced to analyze trends in AR strength and size across the three periods, while Mann-Whitney U tests compared AR strength across the three periods. Additional analyses looked at the contribution of extreme landfalling ARs to high-intensity 6-hourly in-situ precipitation recorded at two high-fidelity stations in New Zealand. Results indicate that extreme ARs are showing the most consistent increasing trends across all three periods, especially the satellite and reference period. Mann-Whitney U tests exhibit statistically significant differences primarily between the pre-satellite and reference period and extreme landfalling ARs account for a disproportionate share of the most intense precipitation events. These findings suggest that extreme ARs provide the most informative lens for understanding future AR impacts in New Zealand and, in the context of independent projections showing future increases in AR-induced extreme precipitation, highlight the importance of resilience planning and adaptive decision-making.","abstract_has_math":false,"creators":["Holgerson, Ryan"],"institution":"Virginia Tech","degree_name":"Master of Science","degree_level":"masters","degree_discipline":"Geography","degree_department":"Geography","school":null,"contributors":[],"advisors":[],"committee_chairs":["Ramseyer, Craig A."],"committee_members":["Bukvic, Anamaria","Ellis, Andrew"],"year":2026,"date_issued":"2026-01-12","date_published":"2026-01-12","updated_at":"2026-07-22T22:20:40Z","subjects":["Atmospheric River","Data Assimilation","IVT","ERA5","Mann-Kendall","Pre-Satellite","Satellite","New Zealand"],"languages":["en"],"rights":["In Copyright"],"rights_urls":["http://rightsstatements.org/vocab/InC/1.0/"],"identifier_entries":[{"key":"dc:identifier.other","label":"Dc Identifier Other","values":["vt_gsexam:45551"],"render_values":[{"text":"vt_gsexam:45551","href":null,"code":true}]}]},"links":{"outbound_url":"https://hdl.handle.net/10919/140763","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.committeechair","label":"Committee Chair","values":["Ramseyer, Craig A."]},{"key":"dc:contributor.committeemember","label":"Committee Member","values":["Bukvic, Anamaria","Ellis, Andrew"]},{"key":"dc:contributor.department","label":"Department","values":["Geography"]},{"key":"dc:creator","label":"Author","values":["Holgerson, Ryan"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2026-01-13T09:00:24Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2026-01-13T09:00:24Z"]},{"key":"dc:date.issued","label":"Date","values":["2026-01-12"]},{"key":"dc:publisher","label":"Institution","values":["Virginia Tech"]},{"key":"dc:type","label":"Dc Type","values":["Thesis"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Geography"]},{"key":"thesis:degree_level","label":"Degree Level","values":["masters"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Master of Science"]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["Virginia Polytechnic Institute and State University"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Atmospheric River","Data Assimilation","IVT","ERA5","Mann-Kendall","Pre-Satellite","Satellite","New Zealand"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language.iso","label":"Language (ISO)","values":["en"]},{"key":"dc:rights","label":"Dc Rights","values":["In Copyright"]},{"key":"dc:rights.uri","label":"Rights URI","values":["http://rightsstatements.org/vocab/InC/1.0/"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.other","label":"Dc Identifier Other","values":["vt_gsexam:45551"]},{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://hdl.handle.net/10919/140763"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["Atmospheric rivers (ARs) are long, narrow corridors of concentrated atmospheric moisture that transport water vapor from the tropics to the middle latitudes where they can drive extreme precipitation and flooding. They have become especially important for New Zealand where ARs are critical for their water resources but also cause societal impacts. This study examines long-term changes in AR frequency, seasonality and strength in New Zealand across a pre-satellite era (1940–1978), satellite era (1979–2023), and modern climate reference period (1991–2020) to account for shifts in observational capability following the advent of satellite data in 1979. ERA5 reanalysis was used to create a regionally tailored atmospheric river detection technique (ARDT) to identify and track ARs across the three periods. The ARDT classified ARs using the 85th and 95th percentiles of integrated vapor transport (IVT) to isolate moderate and extreme ARs and assess their sensitivity across the three periods. Mann-Kendall tests were produced to analyze trends in AR strength and size across the three periods, while Mann-Whitney U tests compared AR strength across the three periods. Additional analyses looked at the contribution of extreme landfalling ARs to high-intensity 6-hourly in-situ precipitation recorded at two high-fidelity stations in New Zealand. Results indicate that extreme ARs are showing the most consistent increasing trends across all three periods, especially the satellite and reference period. Mann-Whitney U tests exhibit statistically significant differences primarily between the pre-satellite and reference period and extreme landfalling ARs account for a disproportionate share of the most intense precipitation events. These findings suggest that extreme ARs provide the most informative lens for understanding future AR impacts in New Zealand and, in the context of independent projections showing future increases in AR-induced extreme precipitation, highlight the importance of resilience planning and adaptive decision-making."]},{"key":"dc:description.abstractgeneral","label":"General Abstract","values":["Atmospheric rivers are long and narrow bands of very moist air that act like \"rivers in the sky\". They carry large amounts of water vapor from the tropics toward the mid-latitudes. When they reach land, they can bring heavy rainfall and flooding. In New Zealand, atmospheric rivers are important because they supply water to many regions and can also disrupt communities and damage infrastructure when they produce extreme rainfall. This study looks at how atmospheric rivers affecting New Zealand have changed over time by examining a pre-satellite era (1940–1978), the satellite era (1979–2023), and a recent modern reference period (1991–2020). These periods were chosen to better understand how improvements in weather observations, especially with the addition of satellite data, may influence what we detect. This study used ERA5 reanalysis data to build a New Zealand-specific tool for identifying and tracking the top 5 and 15 percent of atmospheric rivers to isolate extreme and moderate events based on the total amount of moisture they carry. Statistical trend tests were used to look for long-term changes in atmospheric river strength and size and to compare how atmospheric river characteristics differ across the three eras. Additional work examined how extreme landfalling atmospheric rivers affect short-term rainfall at two well-monitored stations. Results reveal that the strongest atmospheric rivers have the clearest intensification over the three periods with the highest intensities in the satellite and reference periods. In addition, the most intense short-term rainfall is closely tied to the most extreme atmospheric river events. These findings suggest that focusing on extreme atmospheric rivers will be crucial for preparing New Zealand for future climate related risks and strengthening community resilience."]},{"key":"dc:description.degree","label":"Dc Description Degree","values":["Master of Science"]},{"key":"dc:format.medium","label":"Dc Format Medium","values":["ETD"]},{"key":"dc:title","label":"Title","values":["Analysis of Variability in Atmospheric River Characteristics in New Zealand from 1940 through 2023"]}]}],"canonical_facts":{"dc:contributor.committeechair":["Ramseyer, Craig A."],"dc:contributor.committeemember":["Bukvic, Anamaria","Ellis, Andrew"],"dc:contributor.department":["Geography"],"dc:creator":["Holgerson, Ryan"],"dc:date.accessioned":["2026-01-13T09:00:24Z"],"dc:date.available":["2026-01-13T09:00:24Z"],"dc:date.issued":["2026-01-12"],"dc:description.abstract":["Atmospheric rivers (ARs) are long, narrow corridors of concentrated atmospheric moisture that transport water vapor from the tropics to the middle latitudes where they can drive extreme precipitation and flooding. They have become especially important for New Zealand where ARs are critical for their water resources but also cause societal impacts. This study examines long-term changes in AR frequency, seasonality and strength in New Zealand across a pre-satellite era (1940–1978), satellite era (1979–2023), and modern climate reference period (1991–2020) to account for shifts in observational capability following the advent of satellite data in 1979. ERA5 reanalysis was used to create a regionally tailored atmospheric river detection technique (ARDT) to identify and track ARs across the three periods. The ARDT classified ARs using the 85th and 95th percentiles of integrated vapor transport (IVT) to isolate moderate and extreme ARs and assess their sensitivity across the three periods. Mann-Kendall tests were produced to analyze trends in AR strength and size across the three periods, while Mann-Whitney U tests compared AR strength across the three periods. Additional analyses looked at the contribution of extreme landfalling ARs to high-intensity 6-hourly in-situ precipitation recorded at two high-fidelity stations in New Zealand. Results indicate that extreme ARs are showing the most consistent increasing trends across all three periods, especially the satellite and reference period. Mann-Whitney U tests exhibit statistically significant differences primarily between the pre-satellite and reference period and extreme landfalling ARs account for a disproportionate share of the most intense precipitation events. These findings suggest that extreme ARs provide the most informative lens for understanding future AR impacts in New Zealand and, in the context of independent projections showing future increases in AR-induced extreme precipitation, highlight the importance of resilience planning and adaptive decision-making."],"dc:description.abstractgeneral":["Atmospheric rivers are long and narrow bands of very moist air that act like \"rivers in the sky\". They carry large amounts of water vapor from the tropics toward the mid-latitudes. When they reach land, they can bring heavy rainfall and flooding. In New Zealand, atmospheric rivers are important because they supply water to many regions and can also disrupt communities and damage infrastructure when they produce extreme rainfall. This study looks at how atmospheric rivers affecting New Zealand have changed over time by examining a pre-satellite era (1940–1978), the satellite era (1979–2023), and a recent modern reference period (1991–2020). These periods were chosen to better understand how improvements in weather observations, especially with the addition of satellite data, may influence what we detect. This study used ERA5 reanalysis data to build a New Zealand-specific tool for identifying and tracking the top 5 and 15 percent of atmospheric rivers to isolate extreme and moderate events based on the total amount of moisture they carry. Statistical trend tests were used to look for long-term changes in atmospheric river strength and size and to compare how atmospheric river characteristics differ across the three eras. Additional work examined how extreme landfalling atmospheric rivers affect short-term rainfall at two well-monitored stations. Results reveal that the strongest atmospheric rivers have the clearest intensification over the three periods with the highest intensities in the satellite and reference periods. In addition, the most intense short-term rainfall is closely tied to the most extreme atmospheric river events. These findings suggest that focusing on extreme atmospheric rivers will be crucial for preparing New Zealand for future climate related risks and strengthening community resilience."],"dc:description.degree":["Master of Science"],"dc:format.medium":["ETD"],"dc:identifier.other":["vt_gsexam:45551"],"dc:identifier.uri":["https://hdl.handle.net/10919/140763"],"dc:language.iso":["en"],"dc:publisher":["Virginia Tech"],"dc:rights":["In Copyright"],"dc:rights.uri":["http://rightsstatements.org/vocab/InC/1.0/"],"dc:subject":["Atmospheric River","Data Assimilation","IVT","ERA5","Mann-Kendall","Pre-Satellite","Satellite","New Zealand"],"dc:title":["Analysis of Variability in Atmospheric River Characteristics in New Zealand from 1940 through 2023"],"dc:type":["Thesis"],"thesis:degree_discipline":["Geography"],"thesis:degree_level":["masters"],"thesis:degree_name":["Master of Science"],"thesis:institution_name":["Virginia Polytechnic Institute and State University"]},"updated_at":"2026-07-22T22:20:40Z"}