Understanding and predicting forest harvesting effects on peak flows in snow environments with nonstationary frequency modelling
department or school: Forestry, Faculty of
data provider: DSpace
degree campus: UBCV
creator: Yu, Joe
issued: 2022-03-31T07:00:00Z
issued: 2020
related degree: Doctor of Philosophy - PhD
degree grantor: University of British Columbia
description: A century of paired watershed studies evaluated the effects of forest harvesting on peak flows by pairing events by equal chronology. This method has recently come under repeated criticism and calls have been made to abandon the practice and pair by equal frequency instead. However, the stationarity assumption imposed by conventional frequency analyses complicates the use of frequency pairing because peak flows contain change-point and trend-shifting nonstationarities caused by continuous harvesting and forest regrowth. Here, a new nonstationary frequency pairing method was introduced to evaluate harvesting effects by allowing the parameters of peak flow frequency distributions to change in time using physically-based covariates. This research falls within the emerging field of “attribution science”, which uses observations and models to identify separately the factors contributing to extremes. The outcomes of applying this new method at five treatment-control, snow-dominated watersheds (37 km2 to 3550 km2) revealed how harvesting increased the magnitude and frequency of not only small (< 10-yr return period) but also large (>10-yr return period) peak flows. This was a consequence of changes to both the means (+28% to +113%) and standard deviations (no effects to +110%) of the peak flow frequency distributions. Large peak flows became 3-4 (10-20) times more frequent in the least (most) sensitive watershed. The different treatment effects reveal contrasting watershed sensitivities to harvesting, owing to different physiographic characteristics and logging histories. Based on the collective outcomes, a physical model encapsulating harvesting effects at the stand- and watershed-levels was developed to advance the probabilistic understanding of the forests and floods relation. Advantages of the new method include: (i) relaxing the watershed size and proximity constraints between control and treatment watersheds; (ii) detecting small levels of change in the peak flow tim…
aggregated CHO: https://circle.library.ubc.ca/rest/handle/2429/73836
note: UNDERSTANDING AND PREDICTING FOREST HARVESTING EFFECTS ON PEAK FLOWS IN SNOW ENVIRONMENTS WITH NONSTATIONARY FREQUENCY MODELLING by JOE YU B.S.F., University of British Columbia, 2011 A DISSERTATION SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES (Forestry) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) March 2020 © Joe Yu, 2020 ii The following individuals certify that they have read, and recommend to the Faculty of Graduate and Postdoctoral Studies for acceptance, the dissertation entitled: Understanding and predicting forest harvesting effects on peak flows in snow environments with nonstationary frequency modelling Submitted by Joe Yu in partial fulfillment of the requirement for the degree of Doctor of Philosophy in Forestry Examining Committee: Younes Alila, Forestry Supervisor Peter Marshall, Forestry Supervisory Committee Member Bruce Larson, Forestry Supervisory Committee Member Guangyu Wang, Forestry University Examiner Roger Beckie, Earth, Ocean and Atmospheric Sciences University Examiner iii Abstract A century of paired watershed studies evaluated the effects of forest harvesting on peak flows by pairing events by equal chronology. This method has recently come under repeated criticism and calls have been made to abandon the practice and pair by equal frequency instead. However, the stationarity assumption imposed by conventional frequency analyses complicates the use of frequency pairing because peak flows contain change-point and trend-shifting nonstationarities caused by continuous harvesting and forest regrowth. Here, a new nonstationary frequency pairing method was introduced to evaluate harvesting effects by allowing the parameters of peak flow frequency distributions to change in time using physically-based covariates. This research falls within the emerging field of “attribution science”, which uses observations and models to identify separately the f…
has type: Thesis/Dissertation
date issued: 2020-05
is shown at: 10.14288/1.0389643
language: eng
degree discipline: Forestry
provider: Vancouver : University of British Columbia Library
publisher: University of British Columbia
rights: Attribution-NonCommercial-NoDerivatives 4.0 International
rights URI: http://creativecommons.org/licenses/by-nc-nd/4.0/
scholar level: Graduate
type: Text
identifier URI: http://hdl.handle.net/2429/73836